Add JSR-305 annotations to public APIs

(Partially) Resolves BATCH-2688

spring-batch-core/src/main/java/org/springframework/batch/core/ItemProcessListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 package org.springframework.batch.core;
 
 import org.springframework.batch.item.ItemProcessor;
+import org.springframework.lang.Nullable;
 
 /**
  * Listener interface for the processing of an item.  Implementations
@@ -24,6 +25,7 @@ import org.springframework.batch.item.ItemProcessor;
  * exceptions thrown by the processor.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public interface ItemProcessListener<T, S> extends StepListener {
@@ -37,13 +39,13 @@ public interface ItemProcessListener<T, S> extends StepListener {
 	
 	/**
 	 * Called after {@link ItemProcessor#process(Object)} returns.  If the
-	 * processor returns null, this method will still be called, with
-	 * a null result, allowing for notification of 'filtered' items.
+	 * processor returns {@code null}, this method will still be called, with
+	 * a {code null} result, allowing for notification of 'filtered' items.
 	 * 
 	 * @param item to be processed
 	 * @param result of processing
 	 */
-	void afterProcess(T item, S result);
+	void afterProcess(T item, @Nullable S result);
 	
 	/**
 	 * Called if an exception was thrown from {@link ItemProcessor#process(Object)}.

spring-batch-core/src/main/java/org/springframework/batch/core/ItemReadListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2008 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,11 +17,13 @@ package org.springframework.batch.core;
 
 import org.springframework.batch.item.ItemReader;
 import org.springframework.batch.item.ItemWriter;
+import org.springframework.lang.Nullable;
 
 /**
  * Listener interface around the reading of an item.
  * 
  * @author Lucas Ward
+ * @author Mahmoud Ben Hassine
  *
  */
 public interface ItemReadListener<T> extends StepListener {
@@ -36,7 +38,7 @@ public interface ItemReadListener<T> extends StepListener {
 	 * 
 	 * @param item returned from read()
 	 */
-	void afterRead(T item);
+	void afterRead(@Nullable T item);
 	
 	/**
 	 * Called if an error occurs while trying to read.

spring-batch-core/src/main/java/org/springframework/batch/core/Job.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package org.springframework.batch.core;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Batch domain object representing a job. Job is an explicit abstraction
  * representing the configuration of a job specified by a developer. It should
@@ -22,7 +24,7 @@ package org.springframework.batch.core;
  * step.
  * 
  * @author Dave Syer
- * 
+ * @author Mahmoud Ben Hassine
  */
 public interface Job {
 
@@ -47,11 +49,12 @@ public interface Job {
 
 	/**
 	 * If clients need to generate new parameters for the next execution in a
-	 * sequence they can use this incrementer. The return value may be null, in
-	 * the case that this job does not have a natural sequence.
+	 * sequence they can use this incrementer. The return value may be {@code null},
+	 * in the case that this job does not have a natural sequence.
 	 * 
 	 * @return in incrementer to be used for creating new parameters
 	 */
+	@Nullable
 	JobParametersIncrementer getJobParametersIncrementer();
 
 	/**
@@ -60,8 +63,8 @@ public interface Job {
 	 * the execution.
 	 * 
 	 * @return a validator that can be used to check parameter values (never
-	 * null)
+	 * {@code null})
 	 */
 	JobParametersValidator getJobParametersValidator();
 
-}
+}

spring-batch-core/src/main/java/org/springframework/batch/core/JobExecution.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2017 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,12 +29,14 @@ import java.util.Set;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.springframework.batch.item.ExecutionContext;
+import org.springframework.lang.Nullable;
 
 /**
  * Batch domain object representing the execution of a job.
  *
  * @author Lucas Ward
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 @SuppressWarnings("serial")
@@ -91,7 +93,7 @@ public class JobExecution extends Entity {
 	 * @param jobConfigurationName {@link String} instance that represents the
 	 * job configuration name (used with JSR-352).
 	 */
-	public JobExecution(JobInstance job, Long id, JobParameters jobParameters, String jobConfigurationName) {
+	public JobExecution(JobInstance job, Long id, @Nullable JobParameters jobParameters, String jobConfigurationName) {
 		super(id);
 		this.jobInstance = job;
 		this.jobParameters = jobParameters == null ? new JobParameters() : jobParameters;

spring-batch-core/src/main/java/org/springframework/batch/core/JobKeyGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,11 +15,14 @@
  */
 package org.springframework.batch.core;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Strategy interface for the generation of the key used in identifying
  * unique {@link JobInstance}.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  * @param <T> The type of the source data used to calculate the key.
  * @since 2.2
@@ -29,10 +32,10 @@ public interface JobKeyGenerator<T> {
 	/**
 	 * Method to generate the unique key used to identify a job instance.
 	 *
-	 * @param source Source information used to generate the key
+	 * @param source Source information used to generate the key (can be {@code null})
 	 *
 	 * @return a unique string identifying the job based on the information
 	 * supplied
 	 */
-	String generateKey(T source);
+	String generateKey(@Nullable T source);
 }

spring-batch-core/src/main/java/org/springframework/batch/core/JobParametersIncrementer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,11 +15,14 @@
  */
 package org.springframework.batch.core;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Interface for obtaining the next {@link JobParameters} in a sequence.
  * 
  * @author Dave Syer
  * @author Lucas Ward
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  */
 public interface JobParametersIncrementer {
@@ -30,8 +33,8 @@ public interface JobParametersIncrementer {
 	 * instance of a job.
 	 * 
 	 * @param parameters the last value used
-	 * @return the next value to use
+	 * @return the next value to use (never {@code null})
 	 */
-	JobParameters getNext(JobParameters parameters);
+	JobParameters getNext(@Nullable JobParameters parameters);
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/JobParametersValidator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010 the original author or authors.
+ * Copyright 2010-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,13 +15,15 @@
  */
 package org.springframework.batch.core;
 
+import org.springframework.lang.Nullable;
 
 /**
  * Strategy interface for a {@link Job} to use in validating its parameters for
  * an execution.
  * 
  * @author Dave Syer
- * 
+ * @author Mahmoud Ben Hassine
+ *
  */
 public interface JobParametersValidator {
 
@@ -29,9 +31,9 @@ public interface JobParametersValidator {
 	 * Check the parameters meet whatever requirements are appropriate, and
 	 * throw an exception if not.
 	 * 
-	 * @param parameters some {@link JobParameters}
+	 * @param parameters some {@link JobParameters} (can be {@code null})
 	 * @throws JobParametersInvalidException if the parameters are invalid
 	 */
-	void validate(JobParameters parameters) throws JobParametersInvalidException;
+	void validate(@Nullable JobParameters parameters) throws JobParametersInvalidException;
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/StepExecutionListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,12 +15,14 @@
  */
 package org.springframework.batch.core;
 
+import org.springframework.lang.Nullable;
 
 /**
  * Listener interface for the lifecycle of a {@link Step}.
  *
  * @author Lucas Ward
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public interface StepExecutionListener extends StepListener {
@@ -44,7 +46,8 @@ public interface StepExecutionListener extends StepListener {
 	 *
 	 * @param stepExecution {@link StepExecution} instance.
 	 * @return an {@link ExitStatus} to combine with the normal value. Return
-	 * null to leave the old value unchanged.
+	 * {@code null} to leave the old value unchanged.
 	 */
+	@Nullable
 	ExitStatus afterStep(StepExecution stepExecution);
 }

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/JobLocator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,12 +17,14 @@ package org.springframework.batch.core.configuration;
 
 import org.springframework.batch.core.Job;
 import org.springframework.batch.core.launch.NoSuchJobException;
+import org.springframework.lang.Nullable;
 
 /**
  * A runtime service locator interface for retrieving job configurations by
  * <code>name</code>.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * 
  */
 public interface JobLocator {
@@ -37,5 +39,5 @@ public interface JobLocator {
 	 * @throws NoSuchJobException if the required configuration can
 	 * not be found.
 	 */
-	Job getJob(String name) throws NoSuchJobException;
+	Job getJob(@Nullable String name) throws NoSuchJobException;
 }

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/annotation/package-info.java

@@ -2,5 +2,9 @@
  * Annotations and builder factories for java based configuration
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.configuration.annotation;
+@NonNullApi
+package org.springframework.batch.core.configuration.annotation;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces for registration and location of job configurations.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.configuration;
+@NonNullApi
+package org.springframework.batch.core.configuration;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/support/DefaultJobLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,7 @@ import org.springframework.batch.core.step.StepLocator;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -45,6 +46,7 @@ import org.springframework.util.Assert;
  *
  * @author Dave Syer
  * @author Stephane Nicoll
+ * @author Mahmoud Ben Hassine
  */
 public class DefaultJobLoader implements JobLoader, InitializingBean {
 
@@ -77,9 +79,9 @@ public class DefaultJobLoader implements JobLoader, InitializingBean {
 	 * Creates a job loader with the job and step registries provided.
 	 *
 	 * @param jobRegistry a {@link JobRegistry}
-	 * @param stepRegistry a {@link StepRegistry}
+	 * @param stepRegistry a {@link StepRegistry} (can be {@code null})
 	 */
-	public DefaultJobLoader(JobRegistry jobRegistry, StepRegistry stepRegistry) {
+	public DefaultJobLoader(JobRegistry jobRegistry, @Nullable StepRegistry stepRegistry) {
 		this.jobRegistry = jobRegistry;
 		this.stepRegistry = stepRegistry;
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/support/GroupAwareJob.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ import org.springframework.batch.core.Job;
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.JobParametersIncrementer;
 import org.springframework.batch.core.JobParametersValidator;
+import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -32,6 +33,7 @@ import org.springframework.util.ClassUtils;
  *
  *
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public class GroupAwareJob implements Job {
@@ -58,10 +60,10 @@ public class GroupAwareJob implements Job {
 	/**
 	 * Create a new {@link Job} with the given group name and delegate.
 	 *
-	 * @param groupName the group name to prepend
+	 * @param groupName the group name to prepend (can be {@code null})
 	 * @param delegate a delegate for the features of a regular Job
 	 */
-	public GroupAwareJob(String groupName, Job delegate) {
+	public GroupAwareJob(@Nullable String groupName, Job delegate) {
 		super();
 		this.groupName = groupName;
 		this.delegate = delegate;
@@ -89,6 +91,7 @@ public class GroupAwareJob implements Job {
 	}
 
 	@Override
+	@Nullable
 	public JobParametersIncrementer getJobParametersIncrementer() {
 		return delegate.getJobParametersIncrementer();
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/support/MapJobRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.batch.core.configuration.DuplicateJobException;
 import org.springframework.batch.core.configuration.JobFactory;
 import org.springframework.batch.core.configuration.JobRegistry;
 import org.springframework.batch.core.launch.NoSuchJobException;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -32,6 +33,7 @@ import org.springframework.util.Assert;
  *
  * @author Dave Syer
  * @author Robert Fischer
+ * @author Mahmoud Ben Hassine
  */
 public class MapJobRegistry implements JobRegistry {
 
@@ -60,7 +62,7 @@ public class MapJobRegistry implements JobRegistry {
 	}
 
 	@Override
-	public Job getJob(String name) throws NoSuchJobException {
+	public Job getJob(@Nullable String name) throws NoSuchJobException {
 		JobFactory factory = map.get(name);
 		if (factory == null) {
 			throw new NoSuchJobException("No job configuration with the name [" + name + "] was registered");

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/support/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of configuration concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.configuration.support;
+@NonNullApi
+package org.springframework.batch.core.configuration.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/xml/package-info.java

@@ -2,5 +2,9 @@
  * Parsers for XML based configuration
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.configuration.xml;
+@NonNullApi
+package org.springframework.batch.core.configuration.xml;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/converter/DefaultJobParametersConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import org.springframework.batch.core.JobParameter;
 import org.springframework.batch.core.JobParameter.ParameterType;
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersBuilder;
+import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
 import java.text.DateFormat;
@@ -58,6 +59,7 @@ import java.util.Properties;
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public class DefaultJobParametersConverter implements JobParametersConverter {
@@ -92,7 +94,7 @@ public class DefaultJobParametersConverter implements JobParametersConverter {
 	 * @see org.springframework.batch.core.converter.JobParametersConverter#getJobParameters(java.util.Properties)
 	 */
 	@Override
-	public JobParameters getJobParameters(Properties props) {
+	public JobParameters getJobParameters(@Nullable Properties props) {
 
 		if (props == null || props.isEmpty()) {
 			return new JobParameters();
@@ -188,7 +190,7 @@ public class DefaultJobParametersConverter implements JobParametersConverter {
 	 * @see org.springframework.batch.core.converter.JobParametersConverter#getProperties(org.springframework.batch.core.JobParameters)
 	 */
 	@Override
-	public Properties getProperties(JobParameters params) {
+	public Properties getProperties(@Nullable JobParameters params) {
 
 		if (params == null || params.isEmpty()) {
 			return new Properties();

spring-batch-core/src/main/java/org/springframework/batch/core/converter/JobParametersConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.Properties;
 
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersBuilder;
+import org.springframework.lang.Nullable;
 
 /**
  * A factory for {@link JobParameters} instances. A job can be executed with
@@ -27,6 +28,7 @@ import org.springframework.batch.core.JobParametersBuilder;
  * This converter allows job parameters to be converted to and from Properties.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * 
  * @see JobParametersBuilder
  * 
@@ -41,7 +43,7 @@ public interface JobParametersConverter {
 	 * @return a {@link JobParameters} properties converted to the correct
 	 * types.
 	 */
-	public JobParameters getJobParameters(Properties properties);
+	JobParameters getJobParameters(@Nullable Properties properties);
 
 	/**
 	 * The inverse operation: get a {@link Properties} instance. If given null
@@ -50,5 +52,5 @@ public interface JobParametersConverter {
 	 * @param params the {@link JobParameters} instance to be converted.
 	 * @return a representation of the parameters as properties
 	 */
-	public Properties getProperties(JobParameters params);
+	Properties getProperties(@Nullable JobParameters params);
 }

spring-batch-core/src/main/java/org/springframework/batch/core/converter/package-info.java

@@ -3,5 +3,9 @@
  * concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.converter;
+@NonNullApi
+package org.springframework.batch.core.converter;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/explore/JobExplorer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import org.springframework.batch.core.JobInstance;
 import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.launch.NoSuchJobException;
 import org.springframework.batch.item.ExecutionContext;
+import org.springframework.lang.Nullable;
 
 /**
  * Entry point for browsing executions of running or historical jobs and steps.
@@ -32,6 +33,7 @@ import org.springframework.batch.item.ExecutionContext;
  * @author Dave Syer
  * @author Michael Minella
  * @author Will Schipp
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  */
 public interface JobExplorer {
@@ -57,7 +59,8 @@ public interface JobExplorer {
 	 * @param executionId the job execution id
 	 * @return the {@link JobExecution} with this id, or null if not found
 	 */
-	JobExecution getJobExecution(Long executionId);
+	@Nullable
+	JobExecution getJobExecution(@Nullable Long executionId);
 
 	/**
 	 * Retrieve a {@link StepExecution} by its id and parent
@@ -71,13 +74,15 @@ public interface JobExplorer {
 	 *
 	 * @see #getJobExecution(Long)
 	 */
-	StepExecution getStepExecution(Long jobExecutionId, Long stepExecutionId);
+	@Nullable
+	StepExecution getStepExecution(@Nullable Long jobExecutionId, @Nullable Long stepExecutionId);
 
 	/**
 	 * @param instanceId {@link Long} id for the jobInstance to obtain.
 	 * @return the {@link JobInstance} with this id, or null
 	 */
-	JobInstance getJobInstance(Long instanceId);
+	@Nullable
+	JobInstance getJobInstance(@Nullable Long instanceId);
 
 	/**
 	 * Retrieve job executions by their job instance. The corresponding step
@@ -99,7 +104,7 @@ public interface JobExplorer {
 	 * @param jobName the name of the job
 	 * @return the set of running executions for jobs with the specified name
 	 */
-	Set<JobExecution> findRunningJobExecutions(String jobName);
+	Set<JobExecution> findRunningJobExecutions(@Nullable String jobName);
 
 	/**
 	 * Query the repository for all unique {@link JobInstance} names (sorted
@@ -131,6 +136,6 @@ public interface JobExplorer {
 	 * @throws NoSuchJobException thrown when there is no {@link JobInstance}
 	 * for the jobName specified.
 	 */
-	int getJobInstanceCount(String jobName) throws NoSuchJobException;
+	int getJobInstanceCount(@Nullable String jobName) throws NoSuchJobException;
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/explore/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces and related classes to support meta data browsing.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.explore;
+@NonNullApi
+package org.springframework.batch.core.explore;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/explore/support/SimpleJobExplorer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.batch.core.repository.dao.ExecutionContextDao;
 import org.springframework.batch.core.repository.dao.JobExecutionDao;
 import org.springframework.batch.core.repository.dao.JobInstanceDao;
 import org.springframework.batch.core.repository.dao.StepExecutionDao;
+import org.springframework.lang.Nullable;
 
 import java.util.List;
 import java.util.Set;
@@ -36,6 +37,7 @@ import java.util.Set;
  * @author Lucas Ward
  * @author Michael Minella
  * @author Will Schipp
+ * @author Mahmoud Ben Hassine
  *
  * @see JobExplorer
  * @see JobInstanceDao
@@ -157,7 +159,7 @@ public class SimpleJobExplorer implements JobExplorer {
 	 * .lang.Long)
 	 */
 	@Override
-	public JobInstance getJobInstance(Long instanceId) {
+	public JobInstance getJobInstance(@Nullable Long instanceId) {
 		return jobInstanceDao.getJobInstance(instanceId);
 	}
 
@@ -187,7 +189,7 @@ public class SimpleJobExplorer implements JobExplorer {
 	 * @see org.springframework.batch.core.explore.JobExplorer#getJobInstanceCount(java.lang.String)
 	 */
 	@Override
-	public int getJobInstanceCount(String jobName) throws NoSuchJobException {
+	public int getJobInstanceCount(@Nullable String jobName) throws NoSuchJobException {
 		return jobInstanceDao.getJobInstanceCount(jobName);
 	}
 

spring-batch-core/src/main/java/org/springframework/batch/core/explore/support/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of explorer concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.explore.support;
+@NonNullApi
+package org.springframework.batch.core.explore.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/job/AbstractJob.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -43,6 +43,7 @@ import org.springframework.batch.core.step.StepLocator;
 import org.springframework.batch.repeat.RepeatException;
 import org.springframework.beans.factory.BeanNameAware;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
@@ -54,6 +55,7 @@ import org.springframework.util.ClassUtils;
  *
  * @author Lucas Ward
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  */
 public abstract class AbstractJob implements Job, StepLocator, BeanNameAware,
 InitializingBean {
@@ -211,6 +213,7 @@ InitializingBean {
 	 * @see org.springframework.batch.core.Job#getJobParametersIncrementer()
 	 */
 	@Override
+	@Nullable
 	public JobParametersIncrementer getJobParametersIncrementer() {
 		return this.jobParametersIncrementer;
 	}
@@ -287,6 +290,8 @@ InitializingBean {
 	@Override
 	public final void execute(JobExecution execution) {
 
+		Assert.notNull(execution, "jobExecution must not be null");
+
 		if (logger.isDebugEnabled()) {
 			logger.debug("Job execution starting: " + execution);
 		}

spring-batch-core/src/main/java/org/springframework/batch/core/job/CompositeJobParametersValidator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2013 the original author or authors.
+ * Copyright 2011-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersInvalidException;
 import org.springframework.batch.core.JobParametersValidator;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -28,6 +29,7 @@ import org.springframework.util.Assert;
  * injected <code>JobParametersValidator</code>s
  *
  * @author Morten Andersen-Gott
+ * @author Mahmoud Ben Hassine
  *
  */
 public class CompositeJobParametersValidator implements JobParametersValidator, InitializingBean {
@@ -42,7 +44,7 @@ public class CompositeJobParametersValidator implements JobParametersValidator,
 	 * @throws JobParametersInvalidException if the parameters are invalid
 	 */
 	@Override
-	public void validate(JobParameters parameters)	throws JobParametersInvalidException {
+	public void validate(@Nullable JobParameters parameters) throws JobParametersInvalidException {
 		for (JobParametersValidator validator : validators) {
 			validator.validate(parameters);
 		}

spring-batch-core/src/main/java/org/springframework/batch/core/job/DefaultJobParametersValidator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2013 the original author or authors.
+ * Copyright 2012-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,12 +24,14 @@ import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersInvalidException;
 import org.springframework.batch.core.JobParametersValidator;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
  * Default implementation of {@link JobParametersValidator}.
  *
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public class DefaultJobParametersValidator implements JobParametersValidator, InitializingBean {
@@ -83,7 +85,7 @@ public class DefaultJobParametersValidator implements JobParametersValidator, In
 	 * @throws JobParametersInvalidException if the parameters are not valid
 	 */
 	@Override
-	public void validate(JobParameters parameters) throws JobParametersInvalidException {
+	public void validate(@Nullable JobParameters parameters) throws JobParametersInvalidException {
 
 		if (parameters == null) {
 			throw new JobParametersInvalidException("The JobParameters can not be null");

spring-batch-core/src/main/java/org/springframework/batch/core/job/builder/package-info.java

@@ -2,5 +2,9 @@
  * Job and flow level builders for java based configuration of batch jobs
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.job.builder;
+@NonNullApi
+package org.springframework.batch.core.job.builder;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/FlowExecutor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,12 +21,14 @@ import org.springframework.batch.core.StartLimitExceededException;
 import org.springframework.batch.core.Step;
 import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.repository.JobRestartException;
+import org.springframework.lang.Nullable;
 
 /**
  * Context and execution strategy for {@link FlowJob} to allow it to delegate
  * its execution step by step.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  */
 public interface FlowExecutor {
@@ -48,6 +50,7 @@ public interface FlowExecutor {
 	/**
 	 * @return the latest {@link StepExecution} or null if there is none
 	 */
+	@Nullable
 	StepExecution getStepExecution();
 
 	/**

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/JobExecutionDecider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@ package org.springframework.batch.core.job.flow;
 
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.StepExecution;
+import org.springframework.lang.Nullable;
 
 /**
  * Interface allowing for programmatic access to the decision on what the status
@@ -25,6 +26,7 @@ import org.springframework.batch.core.StepExecution;
  * implementation could check that value to determine the status of the flow. 
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  */
 public interface JobExecutionDecider {
@@ -35,9 +37,9 @@ public interface JobExecutionDecider {
 	 * determine the next step in the job.
 	 * 
 	 * @param jobExecution a job execution
-	 * @param stepExecution the latest step execution (may be null)
+	 * @param stepExecution the latest step execution (may be {@code null})
 	 * @return the exit status code
 	 */
-	FlowExecutionStatus decide(JobExecution jobExecution, StepExecution stepExecution);
+	FlowExecutionStatus decide(JobExecution jobExecution, @Nullable StepExecution stepExecution);
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/JobFlowExecutor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@ import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.job.StepHandler;
 import org.springframework.batch.core.repository.JobRepository;
 import org.springframework.batch.core.repository.JobRestartException;
+import org.springframework.lang.Nullable;
 
 /**
  * Implementation of {@link FlowExecutor} for use in components that need to
@@ -33,6 +34,7 @@ import org.springframework.batch.core.repository.JobRestartException;
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public class JobFlowExecutor implements FlowExecutor {
@@ -108,6 +110,7 @@ public class JobFlowExecutor implements FlowExecutor {
 	}
 
 	@Override
+	@Nullable
 	public StepExecution getStepExecution() {
 		return stepExecutionHolder.get();
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/package-info.java

@@ -2,5 +2,9 @@
  * Flow related constructs including Flow interface, executors, and related exceptions
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.job.flow;
+@NonNullApi
+package org.springframework.batch.core.job.flow;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/support/StateTransition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.batch.core.job.flow.support;
 import org.springframework.batch.core.ExitStatus;
 import org.springframework.batch.core.job.flow.State;
 import org.springframework.batch.support.PatternMatcher;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
@@ -29,6 +30,7 @@ import org.springframework.util.StringUtils;
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  */
 public final class StateTransition {
@@ -108,15 +110,15 @@ public final class StateTransition {
 	 * @param state the {@link State} used to generate the outcome for this
 	 * transition
 	 * @param pattern the pattern to match in the exit status of the
-	 * {@link State}
-	 * @param next the name of the next {@link State} to execute
+	 * {@link State} (can be {@code null})
+	 * @param next the name of the next {@link State} to execute (can be {@code null})
 	 * @return {@link StateTransition} that was created.
 	 */
-	public static StateTransition createStateTransition(State state, String pattern, String next) {
+	public static StateTransition createStateTransition(State state, @Nullable String pattern, @Nullable String next) {
 		return new StateTransition(state, pattern, next);
 	}
 
-	private StateTransition(State state, String pattern, String next) {
+	private StateTransition(State state, @Nullable String pattern, @Nullable String next) {
 		super();
 		if (!StringUtils.hasText(pattern)) {
 			this.pattern = "*";

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/support/package-info.java

@@ -2,5 +2,9 @@
  * Basic implementations of flow constructs
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.job.flow.support;
+@NonNullApi
+package org.springframework.batch.core.job.flow.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/job/flow/support/state/package-info.java

@@ -2,5 +2,9 @@
  * States used in defining the underlying Spring Batch state machine
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.job.flow.support.state;
+@NonNullApi
+package org.springframework.batch.core.job.flow.support.state;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/job/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of job concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.job;
+@NonNullApi
+package org.springframework.batch.core.job;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/ItemProcessListenerAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,12 +18,14 @@ package org.springframework.batch.core.jsr;
 import javax.batch.operations.BatchRuntimeException;
 
 import org.springframework.batch.core.ItemProcessListener;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
  * Wrapper class for {@link javax.batch.api.chunk.listener.ItemProcessListener}
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  * @param <T> input type
  * @param <S> output type
@@ -51,7 +53,7 @@ public class ItemProcessListenerAdapter<T,S> implements ItemProcessListener<T, S
 	}
 
 	@Override
-	public void afterProcess(T item, S result) {
+	public void afterProcess(T item, @Nullable S result) {
 		try {
 			delegate.afterProcess(item, result);
 		} catch (Exception e) {

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/ItemReadListenerAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ import javax.batch.operations.BatchRuntimeException;
 
 import org.springframework.batch.core.ItemReadListener;
 import org.springframework.batch.item.ItemReader;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -26,6 +27,7 @@ import org.springframework.util.Assert;
  * a {@link ItemReadListener}.
  * 
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  * @param <T> type to be returned via a read on the associated {@link ItemReader}
  * @since 3.0
@@ -49,7 +51,7 @@ public class ItemReadListenerAdapter<T> implements ItemReadListener<T> {
 	}
 
 	@Override
-	public void afterRead(T item) {
+	public void afterRead(@Nullable T item) {
 		try {
 			delegate.afterRead(item);
 		} catch (Exception e) {

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/JsrJobContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import javax.batch.runtime.BatchStatus;
 
 import org.springframework.batch.core.ExitStatus;
 import org.springframework.batch.core.JobExecution;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -31,6 +32,7 @@ import org.springframework.util.Assert;
  *
  * @author Michael Minella
  * @author Chris Schaefer
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public class JsrJobContext implements javax.batch.runtime.context.JobContext {
@@ -44,7 +46,7 @@ public class JsrJobContext implements javax.batch.runtime.context.JobContext {
 		this.jobExecution = jobExecution;
 	}
 
-	public void setProperties(Properties properties) {
+	public void setProperties(@Nullable Properties properties) {
 		this.properties = properties != null ? properties : new Properties();
 	}
 
@@ -108,6 +110,7 @@ public class JsrJobContext implements javax.batch.runtime.context.JobContext {
 	 * @see javax.batch.runtime.context.JobContext#getExitStatus()
 	 */
 	@Override
+	@Nullable
 	public String getExitStatus() {
 		return exitStatusSet.get() ? jobExecution.getExitStatus().getExitCode() : null;
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/JsrJobParametersConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.batch.item.database.support.DefaultDataFieldMaxValueI
 import org.springframework.batch.support.DatabaseType;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.jdbc.support.incrementer.DataFieldMaxValueIncrementer;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -43,6 +44,7 @@ import org.springframework.util.Assert;
  * for BATCH_JOB_INSTANCE records.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public class JsrJobParametersConverter implements JobParametersConverter, InitializingBean {
@@ -82,7 +84,7 @@ public class JsrJobParametersConverter implements JobParametersConverter, Initia
 	 * @see org.springframework.batch.core.converter.JobParametersConverter#getJobParameters(java.util.Properties)
 	 */
 	@Override
-	public JobParameters getJobParameters(Properties properties) {
+	public JobParameters getJobParameters(@Nullable Properties properties) {
 		JobParametersBuilder builder = new JobParametersBuilder();
 		boolean runIdFound = false;
 
@@ -110,7 +112,7 @@ public class JsrJobParametersConverter implements JobParametersConverter, Initia
 	 * @see org.springframework.batch.core.converter.JobParametersConverter#getProperties(org.springframework.batch.core.JobParameters)
 	 */
 	@Override
-	public Properties getProperties(JobParameters params) {
+	public Properties getProperties(@Nullable JobParameters params) {
 		Properties properties = new Properties();
 		boolean runIdFound = false;
 

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/configuration/support/package-info.java

@@ -2,5 +2,9 @@
  * Extensions of Spring components to support JSR-352 functionality.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.configuration.support;
+@NonNullApi
+package org.springframework.batch.core.jsr.configuration.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/configuration/xml/package-info.java

@@ -2,5 +2,9 @@
  * XML parsers for JSR-352 based Job Specification Language (JSL).
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.configuration.xml;
+@NonNullApi
+package org.springframework.batch.core.jsr.configuration.xml;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/job/flow/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 specific extensions of Flow constructs (executor and job).
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.job.flow;
+@NonNullApi
+package org.springframework.batch.core.jsr.job.flow;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/job/flow/support/JsrFlow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2014 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.batch.core.job.flow.support.SimpleFlow;
 import org.springframework.batch.core.job.flow.support.StateTransition;
 import org.springframework.batch.core.jsr.job.flow.support.state.JsrStepState;
 import org.springframework.batch.item.ExecutionContext;
+import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
 /**
@@ -38,6 +39,7 @@ import org.springframework.util.StringUtils;
  * attempts fail, the flow will fail due to the inability to find the next state.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public class JsrFlow extends SimpleFlow {
@@ -51,6 +53,7 @@ public class JsrFlow extends SimpleFlow {
 		super(name);
 	}
 
+	@Nullable
 	public String getMostRecentStepName() {
 		if(currentStep != null) {
 			return currentStep.getStep().getName();

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/job/flow/support/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 specific flow extensions.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.job.flow.support;
+@NonNullApi
+package org.springframework.batch.core.jsr.job.flow.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/job/flow/support/state/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 specific states used in flow execution.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.job.flow.support.state;
+@NonNullApi
+package org.springframework.batch.core.jsr.job.flow.support.state;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/job/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 specific handler implementations.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.job;
+@NonNullApi
+package org.springframework.batch.core.jsr.job;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/launch/package-info.java

@@ -2,5 +2,9 @@
  * Implementation of the JSR-352 specific job launching facilities.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.launch;
+@NonNullApi
+package org.springframework.batch.core.jsr.launch;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/package-info.java

@@ -2,5 +2,9 @@
  * Extensions of core batch components to apply JSR-352 specific logic.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr;
+@NonNullApi
+package org.springframework.batch.core.jsr;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/partition/package-info.java

@@ -2,5 +2,9 @@
  * Implementation of JSR-352 specific partitioning extensions.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.partition;
+@NonNullApi
+package org.springframework.batch.core.jsr.partition;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/partition/support/package-info.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Support classes for JSR-352 partitioning configuration.
+ *
+ * @author Mahmoud Ben Hassine
+ */
+@NonNullApi
+package org.springframework.batch.core.jsr.partition.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/step/batchlet/package-info.java

@@ -2,5 +2,9 @@
  * Classes for supporting JSR-352's {@link javax.batch.api.Batchlet}.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.step.batchlet;
+@NonNullApi
+package org.springframework.batch.core.jsr.step.batchlet;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/step/builder/package-info.java

@@ -2,5 +2,9 @@
  * Extensions to step related builders to implement JSR-352 specific functionality
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.step.builder;
+@NonNullApi
+package org.springframework.batch.core.jsr.step.builder;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/step/item/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 specific components for implementing item based processing including fault tolerance.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.step.item;
+@NonNullApi
+package org.springframework.batch.core.jsr.step.item;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/jsr/step/package-info.java

@@ -2,5 +2,9 @@
  * JSR-352 extensions of existing batch {@link org.springframework.batch.core.Step} types.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.jsr.step;
+@NonNullApi
+package org.springframework.batch.core.jsr.step;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/launch/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces and simple implementations of launch concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.launch;
+@NonNullApi
+package org.springframework.batch.core.launch;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/launch/support/RunIdIncrementer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,9 +18,11 @@ package org.springframework.batch.core.launch.support;
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersBuilder;
 import org.springframework.batch.core.JobParametersIncrementer;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  */
 public class RunIdIncrementer implements JobParametersIncrementer {
 
@@ -41,7 +43,7 @@ public class RunIdIncrementer implements JobParametersIncrementer {
 	 * Increment the run.id parameter (starting with 1).
 	 */
 	@Override
-	public JobParameters getNext(JobParameters parameters) {
+	public JobParameters getNext(@Nullable JobParameters parameters) {
 
 		JobParameters params = (parameters == null) ? new JobParameters() : parameters;
 

spring-batch-core/src/main/java/org/springframework/batch/core/launch/support/ScheduledJobParametersFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,9 +27,11 @@ import org.springframework.batch.core.JobParameter;
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.JobParametersBuilder;
 import org.springframework.batch.core.converter.JobParametersConverter;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Lucas Ward
+ * @author Mahmoud Ben Hassine
  *
  */
 public class ScheduledJobParametersFactory implements JobParametersConverter {
@@ -44,7 +46,7 @@ public class ScheduledJobParametersFactory implements JobParametersConverter {
 	 * @see org.springframework.batch.core.runtime.JobParametersFactory#getJobParameters(java.util.Properties)
 	 */
 	@Override
-	public JobParameters getJobParameters(Properties props) {
+	public JobParameters getJobParameters(@Nullable Properties props) {
 
 		if (props == null || props.isEmpty()) {
 			return new JobParameters();
@@ -75,7 +77,7 @@ public class ScheduledJobParametersFactory implements JobParametersConverter {
 	 * @see org.springframework.batch.core.converter.JobParametersConverter#getProperties(org.springframework.batch.core.JobParameters)
 	 */
 	@Override
-	public Properties getProperties(JobParameters params) {
+	public Properties getProperties(@Nullable JobParameters params) {
 
 		if (params == null || params.isEmpty()) {
 			return new Properties();

spring-batch-core/src/main/java/org/springframework/batch/core/launch/support/package-info.java

@@ -2,5 +2,9 @@
  * Support classes for use in bootstrap and launch implementations or configurations.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.launch.support;
+@NonNullApi
+package org.springframework.batch.core.launch.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/listener/CompositeItemProcessListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,9 +20,11 @@ import java.util.List;
 
 import org.springframework.batch.core.ItemProcessListener;
 import org.springframework.core.Ordered;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public class CompositeItemProcessListener<T, S> implements ItemProcessListener<T, S> {
@@ -54,7 +56,7 @@ public class CompositeItemProcessListener<T, S> implements ItemProcessListener<T
 	 * java.lang.Object)
 	 */
 	@Override
-	public void afterProcess(T item, S result) {
+	public void afterProcess(T item, @Nullable S result) {
 		for (Iterator<ItemProcessListener<? super T, ? super S>> iterator = listeners.reverse(); iterator.hasNext();) {
 			ItemProcessListener<? super T, ? super S> listener = iterator.next();
 			listener.afterProcess(item, result);

spring-batch-core/src/main/java/org/springframework/batch/core/listener/ItemListenerSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.List;
 import org.springframework.batch.core.ItemProcessListener;
 import org.springframework.batch.core.ItemReadListener;
 import org.springframework.batch.core.ItemWriteListener;
+import org.springframework.lang.Nullable;
 
 /**
  * Basic no-op implementation of the {@link ItemReadListener},
@@ -28,6 +29,7 @@ import org.springframework.batch.core.ItemWriteListener;
  * at once.
  *
  * @author Lucas Ward
+ * @author Mahmoud Ben Hassine
  *
  */
 public class ItemListenerSupport<I, O> implements ItemReadListener<I>, ItemProcessListener<I, O>, ItemWriteListener<O> {
@@ -66,7 +68,7 @@ public class ItemListenerSupport<I, O> implements ItemReadListener<I>, ItemProce
 	 *      java.lang.Object)
 	 */
 	@Override
-	public void afterProcess(I item, O result) {
+	public void afterProcess(I item, @Nullable O result) {
 	}
 
 	/*

spring-batch-core/src/main/java/org/springframework/batch/core/listener/JobListenerMetaData.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,12 +23,14 @@ import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.JobExecutionListener;
 import org.springframework.batch.core.annotation.AfterJob;
 import org.springframework.batch.core.annotation.BeforeJob;
+import org.springframework.lang.Nullable;
 
 /**
  * Enumeration for {@link JobExecutionListener} meta data, which ties together the names
  * of methods, their interfaces, annotation, and expected arguments.
  *
  * @author Lucas Ward
+ * @author Mahmoud Ben Hassine
  * @since 2.0
  * @see JobListenerFactoryBean
  */
@@ -85,8 +87,9 @@ public enum JobListenerMetaData implements ListenerMetaData {
 	 * Return the relevant meta data for the provided property name.
 	 *
 	 * @param propertyName name of the property to retrieve.
-	 * @return meta data with supplied property name, null if none exists.
+	 * @return meta data with supplied property name, {@code null} if none exists.
 	 */
+	@Nullable
 	public static JobListenerMetaData fromPropertyName(String propertyName){
 		return propertyMap.get(propertyName);
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/listener/MulticasterBatchListener.java

@@ -33,6 +33,7 @@ import org.springframework.batch.core.StepExecutionListener;
 import org.springframework.batch.core.StepListener;
 import org.springframework.batch.core.scope.context.ChunkContext;
 import org.springframework.batch.item.ItemStream;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Dave Syer
@@ -130,7 +131,7 @@ ItemProcessListener<T, S>, ItemWriteListener<S>, SkipListener<T, S>, RetryReadLi
 	 * java.lang.Object)
 	 */
 	@Override
-	public void afterProcess(T item, S result) {
+	public void afterProcess(T item, @Nullable S result) {
 		try {
 			itemProcessListener.afterProcess(item, result);
 		}
@@ -222,7 +223,7 @@ ItemProcessListener<T, S>, ItemWriteListener<S>, SkipListener<T, S>, RetryReadLi
 	 * @see org.springframework.batch.core.listener.CompositeItemReadListener#afterRead(java.lang.Object)
 	 */
 	@Override
-	public void afterRead(T item) {
+	public void afterRead(@Nullable T item) {
 		try {
 			itemReadListener.afterRead(item);
 		}

spring-batch-core/src/main/java/org/springframework/batch/core/listener/StepListenerSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,12 +27,14 @@ import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.StepExecutionListener;
 import org.springframework.batch.core.StepListener;
 import org.springframework.batch.core.scope.context.ChunkContext;
+import org.springframework.lang.Nullable;
 
 /**
  * Basic no-op implementations of all {@link StepListener} interfaces.
  *
  * @author Lucas Ward
  * @author Robert Kasanicky
+ * @author Mahmoud Ben Hassine
  */
 public class StepListenerSupport<T,S> implements StepExecutionListener, ChunkListener,
 ItemReadListener<T>, ItemProcessListener<T,S>, ItemWriteListener<S>, SkipListener<T, S> {
@@ -70,7 +72,7 @@ ItemReadListener<T>, ItemProcessListener<T,S>, ItemWriteListener<S>, SkipListene
 	 * @see org.springframework.batch.core.domain.ItemReadListener#afterRead(java.lang.Object)
 	 */
 	@Override
-	public void afterRead(T item) {
+	public void afterRead(@Nullable T item) {
 	}
 
 	/* (non-Javadoc)
@@ -112,7 +114,7 @@ ItemReadListener<T>, ItemProcessListener<T,S>, ItemWriteListener<S>, SkipListene
 	 * @see org.springframework.batch.core.ItemProcessListener#afterProcess(java.lang.Object, java.lang.Object)
 	 */
 	@Override
-	public void afterProcess(T item, S result) {
+	public void afterProcess(T item, @Nullable S result) {
 	}
 
 	/* (non-Javadoc)

spring-batch-core/src/main/java/org/springframework/batch/core/listener/package-info.java

@@ -2,5 +2,9 @@
  * Generic implementations of core batch listener interfaces.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.listener;
+@NonNullApi
+package org.springframework.batch.core.listener;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/package-info.java

@@ -4,5 +4,9 @@
  * There is a reference implementation of the core interfaces in the execution module.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core;
+@NonNullApi
+package org.springframework.batch.core;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/partition/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces for partitioning components.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.partition;
+@NonNullApi
+package org.springframework.batch.core.partition;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/partition/support/package-info.java

@@ -2,5 +2,9 @@
  * Implementation of common partition components.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.partition.support;
+@NonNullApi
+package org.springframework.batch.core.partition.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/repository/JobRepository.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.repository.dao.JobExecutionDao;
 import org.springframework.batch.core.repository.dao.JobInstanceDao;
 import org.springframework.batch.item.ExecutionContext;
+import org.springframework.lang.Nullable;
 import org.springframework.transaction.annotation.Isolation;
 
 import java.util.Collection;
@@ -43,6 +44,7 @@ import java.util.Collection;
  * @author Robert Kasanicky
  * @author David Turanski
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
 public interface JobRepository {
 
@@ -181,6 +183,7 @@ public interface JobRepository {
 	 * @param stepName the name of the step execution that might have run.
 	 * @return the last execution of step for the given job instance.
 	 */
+	@Nullable
 	StepExecution getLastStepExecution(JobInstance jobInstance, String stepName);
 
 	/**
@@ -195,6 +198,7 @@ public interface JobRepository {
 	 * @param jobParameters parameters identifying the {@link JobInstance}
 	 * @return the last execution of job if exists, null otherwise
 	 */
+	@Nullable
 	JobExecution getLastJobExecution(String jobName, JobParameters jobParameters);
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcJobExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -43,6 +43,7 @@ import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.jdbc.core.RowCallbackHandler;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.support.incrementer.DataFieldMaxValueIncrementer;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -58,6 +59,7 @@ import org.springframework.util.Assert;
  * @author Dave Syer
  * @author Robert Kasanicky
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
 public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements JobExecutionDao, InitializingBean {
 
@@ -241,7 +243,7 @@ public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements
 	}
 
 	@Override
-	public JobExecution getLastJobExecution(JobInstance jobInstance) {
+	public JobExecution getLastJobExecution(@Nullable JobInstance jobInstance) {
 
 		Long id = jobInstance.getId();
 
@@ -265,6 +267,7 @@ public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements
 	 * getLastJobExecution(java.lang.String)
 	 */
 	@Override
+	@Nullable
 	public JobExecution getJobExecution(Long executionId) {
 		try {
 			JobExecution jobExecution = getJdbcTemplate().queryForObject(getQuery(GET_EXECUTION_BY_ID),

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcJobInstanceDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,7 @@ import org.springframework.dao.EmptyResultDataAccessException;
 import org.springframework.jdbc.core.ResultSetExtractor;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.support.incrementer.DataFieldMaxValueIncrementer;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
@@ -51,6 +52,7 @@ import org.springframework.util.StringUtils;
  * @author Robert Kasanicky
  * @author Michael Minella
  * @author Will Schipp
+ * @author Mahmoud Ben Hassine
  */
 public class JdbcJobInstanceDao extends AbstractJdbcBatchMetadataDao implements
 JobInstanceDao, InitializingBean {
@@ -130,6 +132,7 @@ JobInstanceDao, InitializingBean {
 	 *             if any {@link JobParameters} fields are null.
 	 */
 	@Override
+	@Nullable
 	public JobInstance getJobInstance(final String jobName,
 			final JobParameters jobParameters) {
 
@@ -166,7 +169,8 @@ JobInstanceDao, InitializingBean {
 	 * (java.lang.Long)
 	 */
 	@Override
-	public JobInstance getJobInstance(Long instanceId) {
+	@Nullable
+	public JobInstance getJobInstance(@Nullable Long instanceId) {
 
 		try {
 			return getJdbcTemplate().queryForObject(getQuery(GET_JOB_FROM_ID),
@@ -241,6 +245,7 @@ JobInstanceDao, InitializingBean {
 	 * (org.springframework.batch.core.JobExecution)
 	 */
 	@Override
+	@Nullable
 	public JobInstance getJobInstance(JobExecution jobExecution) {
 
 		try {
@@ -256,7 +261,7 @@ JobInstanceDao, InitializingBean {
 	 * @see org.springframework.batch.core.repository.dao.JobInstanceDao#getJobInstanceCount(java.lang.String)
 	 */
 	@Override
-	public int getJobInstanceCount(String jobName) throws NoSuchJobException {
+	public int getJobInstanceCount(@Nullable String jobName) throws NoSuchJobException {
 
 		try {
 			return getJdbcTemplate().queryForObject(

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcStepExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,6 +39,7 @@ import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.jdbc.core.BatchPreparedStatementSetter;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.support.incrementer.DataFieldMaxValueIncrementer;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -58,6 +59,7 @@ import org.springframework.util.Assert;
  * @author Dave Syer
  * @author Robert Kasanicky
  * @author David Turanski
+ * @author Mahmoud Ben Hassine
  *
  * @see StepExecutionDao
  */
@@ -281,6 +283,7 @@ public class JdbcStepExecutionDao extends AbstractJdbcBatchMetadataDao implement
 	}
 
 	@Override
+	@Nullable
 	public StepExecution getStepExecution(JobExecution jobExecution, Long stepExecutionId) {
 		List<StepExecution> executions = getJdbcTemplate().query(getQuery(GET_STEP_EXECUTION),
 				new StepExecutionRowMapper(jobExecution), jobExecution.getId(), stepExecutionId);

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JobExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,12 +21,14 @@ import java.util.Set;
 
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.JobInstance;
+import org.springframework.lang.Nullable;
 
 /**
  * Data Access Object for job executions.
  * 
  * @author Lucas Ward
  * @author Robert Kasanicky
+ * @author Mahmoud Ben Hassine
  */
 public interface JobExecutionDao {
 
@@ -63,8 +65,10 @@ public interface JobExecutionDao {
 	 * Find the last {@link JobExecution} to have been created for a given
 	 * {@link JobInstance}.
 	 * @param jobInstance the {@link JobInstance}
-	 * @return the last {@link JobExecution} to execute for this instance
+	 * @return the last {@link JobExecution} to execute for this instance or
+	 * {@code null} if no job execution is found for the given job instance.
 	 */
+	@Nullable
 	JobExecution getLastJobExecution(JobInstance jobInstance);
 
 	/**
@@ -78,6 +82,7 @@ public interface JobExecutionDao {
 	 * @param executionId {@link Long} containing the id of the execution.
 	 * @return the {@link JobExecution} for given identifier.
 	 */
+	@Nullable
 	JobExecution getJobExecution(Long executionId);
 
 	/**

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JobInstanceDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.JobInstance;
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.launch.NoSuchJobException;
+import org.springframework.lang.Nullable;
 
 /**
  * Data Access Object for job instances.
@@ -29,6 +30,7 @@ import org.springframework.batch.core.launch.NoSuchJobException;
  * @author Lucas Ward
  * @author Robert Kasanicky
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public interface JobInstanceDao {
@@ -56,24 +58,27 @@ public interface JobInstanceDao {
 	 * @param jobName the name of the job
 	 * @param jobParameters the parameters with which the job was executed
 	 * @return {@link JobInstance} object matching the job name and
-	 * {@link JobParameters} or null
+	 * {@link JobParameters} or {@code null}
 	 */
+	@Nullable
 	JobInstance getJobInstance(String jobName, JobParameters jobParameters);
 
 	/**
 	 * Fetch the job instance with the provided identifier.
 	 *
 	 * @param instanceId the job identifier
-	 * @return the job instance with this identifier or null if it doesn't exist
+	 * @return the job instance with this identifier or {@code null} if it doesn't exist
 	 */
-	JobInstance getJobInstance(Long instanceId);
+	@Nullable
+	JobInstance getJobInstance(@Nullable Long instanceId);
 
 	/**
 	 * Fetch the JobInstance for the provided JobExecution.
 	 *
 	 * @param jobExecution the JobExecution
-	 * @return the JobInstance for the provided execution or null if it doesn't exist.
+	 * @return the JobInstance for the provided execution or {@code null} if it doesn't exist.
 	 */
+	@Nullable
 	JobInstance getJobInstance(JobExecution jobExecution);
 
 	/**
@@ -122,6 +127,6 @@ public interface JobInstanceDao {
 	 *
 	 * @throws NoSuchJobException thrown if no Job has the jobName specified.
 	 */
-	int getJobInstanceCount(String jobName) throws NoSuchJobException;
+	int getJobInstanceCount(@Nullable String jobName) throws NoSuchJobException;
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapJobExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import java.util.concurrent.atomic.AtomicLong;
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.JobInstance;
 import org.springframework.dao.OptimisticLockingFailureException;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.SerializationUtils;
 
@@ -106,7 +107,7 @@ public class MapJobExecutionDao implements JobExecutionDao {
 	}
 
 	@Override
-	public JobExecution getLastJobExecution(JobInstance jobInstance) {
+	public JobExecution getLastJobExecution(@Nullable JobInstance jobInstance) {
 		JobExecution lastExec = null;
 		for (JobExecution exec : executionsById.values()) {
 			if (!exec.getJobInstance().equals(jobInstance)) {
@@ -148,6 +149,7 @@ public class MapJobExecutionDao implements JobExecutionDao {
 	 * (java.lang.Long)
 	 */
 	@Override
+	@Nullable
 	public JobExecution getJobExecution(Long executionId) {
 		return copy(executionsById.get(executionId));
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapJobInstanceDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,6 +30,7 @@ import org.springframework.batch.core.JobInstance;
 import org.springframework.batch.core.JobKeyGenerator;
 import org.springframework.batch.core.JobParameters;
 import org.springframework.batch.core.launch.NoSuchJobException;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -63,12 +64,14 @@ public class MapJobInstanceDao implements JobInstanceDao {
 	}
 
 	@Override
+	@Nullable
 	public JobInstance getJobInstance(String jobName, JobParameters jobParameters) {
 		return jobInstances.get(jobName + "|" + jobKeyGenerator.generateKey(jobParameters));
 	}
 
 	@Override
-	public JobInstance getJobInstance(Long instanceId) {
+	@Nullable
+	public JobInstance getJobInstance(@Nullable Long instanceId) {
 		for (Map.Entry<String, JobInstance> instanceEntry : jobInstances.entrySet()) {
 			JobInstance instance = instanceEntry.getValue();
 			if (instance.getId().equals(instanceId)) {
@@ -104,12 +107,13 @@ public class MapJobInstanceDao implements JobInstanceDao {
 	}
 
 	@Override
+	@Nullable
 	public JobInstance getJobInstance(JobExecution jobExecution) {
 		return jobExecution.getJobInstance();
 	}
 
 	@Override
-	public int getJobInstanceCount(String jobName) throws NoSuchJobException {
+	public int getJobInstanceCount(@Nullable String jobName) throws NoSuchJobException {
 		int count = 0;
 
 		for (Map.Entry<String, JobInstance> instanceEntry : jobInstances.entrySet()) {

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapStepExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.batch.core.Entity;
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.StepExecution;
 import org.springframework.dao.OptimisticLockingFailureException;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.util.SerializationUtils;
@@ -113,6 +114,7 @@ public class MapStepExecutionDao implements StepExecutionDao {
 	}
 
 	@Override
+	@Nullable
 	public StepExecution getStepExecution(JobExecution jobExecution, Long stepExecutionId) {
 		return executionsByStepExecutionId.get(stepExecutionId);
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/StepExecutionDao.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.Collection;
 
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.StepExecution;
+import org.springframework.lang.Nullable;
 
 public interface StepExecutionDao {
 
@@ -61,6 +62,7 @@ public interface StepExecutionDao {
 	 * @param stepExecutionId the step execution id
 	 * @return a {@link StepExecution}
 	 */
+	@Nullable
 	StepExecution getStepExecution(JobExecution jobExecution, Long stepExecutionId);
 
 	/**

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of dao concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.repository.dao;
+@NonNullApi
+package org.springframework.batch.core.repository.dao;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/repository/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces and generic implementations of repository concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.repository;
+@NonNullApi
+package org.springframework.batch.core.repository;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/repository/support/SimpleJobRepository.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2014 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,6 +32,7 @@ import org.springframework.batch.core.repository.dao.JobExecutionDao;
 import org.springframework.batch.core.repository.dao.JobInstanceDao;
 import org.springframework.batch.core.repository.dao.StepExecutionDao;
 import org.springframework.batch.item.ExecutionContext;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 import java.util.ArrayList;
@@ -50,6 +51,7 @@ import java.util.List;
  * @author Dave Syer
  * @author Robert Kasanicky
  * @author David Turanski
+ * @author Mahmoud Ben Hassine
  *
  * @see JobRepository
  * @see JobInstanceDao
@@ -215,6 +217,7 @@ public class SimpleJobRepository implements JobRepository {
 	}
 
 	@Override
+	@Nullable
 	public StepExecution getLastStepExecution(JobInstance jobInstance, String stepName) {
 		List<JobExecution> jobExecutions = jobExecutionDao.findJobExecutions(jobInstance);
 		List<StepExecution> stepExecutions = new ArrayList<StepExecution>(jobExecutions.size());
@@ -289,6 +292,7 @@ public class SimpleJobRepository implements JobRepository {
 	}
 
 	@Override
+	@Nullable
 	public JobExecution getLastJobExecution(String jobName, JobParameters jobParameters) {
 		JobInstance jobInstance = jobInstanceDao.getJobInstance(jobName, jobParameters);
 		if (jobInstance == null) {

spring-batch-core/src/main/java/org/springframework/batch/core/repository/support/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of repository concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.repository.support;
+@NonNullApi
+package org.springframework.batch.core.repository.support;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/JobContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,7 @@ import org.springframework.batch.core.UnexpectedJobExecutionException;
 import org.springframework.batch.core.scope.StepScope;
 import org.springframework.batch.item.ExecutionContext;
 import org.springframework.batch.repeat.context.SynchronizedAttributeAccessor;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -44,6 +45,7 @@ import org.springframework.util.Assert;
  *
  * @author Dave Syer
  * @author Jimmy Praet (create JobContext based on {@link StepContext})
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public class JobContext extends SynchronizedAttributeAccessor {
@@ -134,6 +136,7 @@ public class JobContext extends SynchronizedAttributeAccessor {
 	 * @see SynchronizedAttributeAccessor#removeAttribute(String)
 	 */
 	@Override
+	@Nullable
 	public Object removeAttribute(String name) {
 		unregisterDestructionCallbacks(name);
 		return super.removeAttribute(name);

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/JobSynchronizationManager.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.batch.core.scope.context;
 import org.springframework.batch.core.Job;
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.jsr.configuration.support.BatchPropertyContext;
+import org.springframework.lang.Nullable;
 
 /**
  * Central convenience class for framework use in managing the job scope
@@ -28,6 +29,7 @@ import org.springframework.batch.core.jsr.configuration.support.BatchPropertyCon
  *
  * @author Dave Syer
  * @author Jimmy Praet
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public class JobSynchronizationManager {
@@ -46,11 +48,12 @@ public class JobSynchronizationManager {
 	};
 
 	/**
-	 * Getter for the current context if there is one, otherwise returns null.
+	 * Getter for the current context if there is one, otherwise returns {@code null}.
 	 *
-	 * @return the current {@link JobContext} or null if there is none (if one
+	 * @return the current {@link JobContext} or {@code null} if there is none (if one
 	 * has not been registered for this thread).
 	 */
+	@Nullable
 	public static JobContext getContext() {
 		return manager.getContext();
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/StepContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,7 @@ import org.springframework.batch.core.jsr.configuration.support.BatchPropertyCon
 import org.springframework.batch.core.scope.StepScope;
 import org.springframework.batch.item.ExecutionContext;
 import org.springframework.batch.repeat.context.SynchronizedAttributeAccessor;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -46,6 +47,7 @@ import org.springframework.util.Assert;
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public class StepContext extends SynchronizedAttributeAccessor {
@@ -184,6 +186,7 @@ public class StepContext extends SynchronizedAttributeAccessor {
 	 * @see SynchronizedAttributeAccessor#removeAttribute(String)
 	 */
 	@Override
+	@Nullable
 	public Object removeAttribute(String name) {
 		unregisterDestructionCallbacks(name);
 		return super.removeAttribute(name);

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/StepContextRepeatCallback.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.repeat.RepeatCallback;
 import org.springframework.batch.repeat.RepeatContext;
 import org.springframework.batch.repeat.RepeatStatus;
+import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -32,6 +33,7 @@ import org.springframework.util.ObjectUtils;
  * callback inside a {@link Step}.
  *
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  *
  */
 public abstract class StepContextRepeatCallback implements RepeatCallback {
@@ -60,6 +62,7 @@ public abstract class StepContextRepeatCallback implements RepeatCallback {
 	 * @see RepeatCallback#doInIteration(RepeatContext)
 	 */
 	@Override
+	@Nullable
 	public RepeatStatus doInIteration(RepeatContext context) throws Exception {
 
 		// The StepContext has to be the same for all chunks,
@@ -106,6 +109,7 @@ public abstract class StepContextRepeatCallback implements RepeatCallback {
 	 * @throws Exception implementations can throw an exception if anything goes
 	 * wrong
 	 */
+	@Nullable
 	public abstract RepeatStatus doInChunkContext(RepeatContext context, ChunkContext chunkContext) throws Exception;
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/StepSynchronizationManager.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.batch.core.scope.context;
 import org.springframework.batch.core.Step;
 import org.springframework.batch.core.StepExecution;
 import org.springframework.batch.core.jsr.configuration.support.BatchPropertyContext;
+import org.springframework.lang.Nullable;
 
 /**
  * Central convenience class for framework use in managing the step scope
@@ -28,6 +29,7 @@ import org.springframework.batch.core.jsr.configuration.support.BatchPropertyCon
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public class StepSynchronizationManager {
@@ -55,11 +57,12 @@ public class StepSynchronizationManager {
 	};
 
 	/**
-	 * Getter for the current context if there is one, otherwise returns null.
+	 * Getter for the current context if there is one, otherwise returns {@code null}.
 	 *
-	 * @return the current {@link StepContext} or null if there is none (if one
+	 * @return the current {@link StepContext} or {@code null} if there is none (if one
 	 * has not been registered for this thread).
 	 */
+	@Nullable
 	public static StepContext getContext() {
 		return manager.getContext();
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/SynchronizationManagerSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.springframework.batch.core.jsr.configuration.support.BatchPropertyContext;
+import org.springframework.lang.Nullable;
 
 
 /**
@@ -29,6 +30,7 @@ import org.springframework.batch.core.jsr.configuration.support.BatchPropertyCon
  *
  * @author Dave Syer
  * @author Jimmy Praet
+ * @author Mahmoud Ben Hassine
  * @since 3.0
  */
 public abstract class SynchronizationManagerSupport<E, C> {
@@ -61,11 +63,12 @@ public abstract class SynchronizationManagerSupport<E, C> {
 	private final Map<E, C> contexts = new ConcurrentHashMap<E, C>();
 
 	/**
-	 * Getter for the current context if there is one, otherwise returns null.
+	 * Getter for the current context if there is one, otherwise returns {@code null}.
 	 *
-	 * @return the current context or null if there is none (if one
+	 * @return the current context or {@code null} if there is none (if one
 	 *         has not been registered for this thread).
 	 */
+	@Nullable
 	public C getContext() {
 		if (getCurrent().isEmpty()) {
 			return null;
@@ -84,7 +87,8 @@ public abstract class SynchronizationManagerSupport<E, C> {
 	 * @return a new context or the current one if it has the same
 	 *         execution
 	 */
-	public C register(E execution) {
+	@Nullable
+	public C register(@Nullable E execution) {
 		if (execution == null) {
 			return null;
 		}
@@ -111,7 +115,8 @@ public abstract class SynchronizationManagerSupport<E, C> {
 	 * @return a new context or the current one if it has the same
 	 *         execution
 	 */
-	public C register(E execution, BatchPropertyContext propertyContext) {
+	@Nullable
+	public C register(@Nullable E execution, @Nullable BatchPropertyContext propertyContext) {
 		if (execution == null) {
 			return null;
 		}
@@ -197,6 +202,6 @@ public abstract class SynchronizationManagerSupport<E, C> {
 
 	protected abstract void close(C context);
 
-	protected abstract C createNewContext(E execution, BatchPropertyContext propertyContext);
+	protected abstract C createNewContext(E execution, @Nullable BatchPropertyContext propertyContext);
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/package-info.java

@@ -2,5 +2,9 @@
  * Implementation of the contexts for each of the custom bean scopes in Spring Batch (Job and Step).
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.scope.context;
+@NonNullApi
+package org.springframework.batch.core.scope.context;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/scope/package-info.java

@@ -2,5 +2,9 @@
  * Implementation of Spring Batch specific bean scopes (Job and Step).
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.scope;
+@NonNullApi
+package org.springframework.batch.core.scope;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/AbstractStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,6 +48,7 @@ import org.springframework.util.ClassUtils;
  * @author Robert Kasanicky
  * @author Michael Minella
  * @author Chris Schaefer
+ * @author Mahmoud Ben Hassine
  */
 public abstract class AbstractStep implements Step, InitializingBean, BeanNameAware {
 
@@ -180,6 +181,8 @@ public abstract class AbstractStep implements Step, InitializingBean, BeanNameAw
 	public final void execute(StepExecution stepExecution) throws JobInterruptedException,
 	UnexpectedJobExecutionException {
 
+		Assert.notNull(stepExecution, "stepExecution must not be null");
+
 		if (logger.isDebugEnabled()) {
 			logger.debug("Executing: id=" + stepExecution.getId());
 		}

spring-batch-core/src/main/java/org/springframework/batch/core/step/builder/package-info.java

@@ -2,5 +2,9 @@
  * Step level builders for java based job configuration.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.builder;
+@NonNullApi
+package org.springframework.batch.core.step.builder;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/factory/package-info.java

@@ -2,5 +2,9 @@
  * Factories for step level components.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.factory;
+@NonNullApi
+package org.springframework.batch.core.step.factory;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/item/SimpleChunkProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.batch.repeat.RepeatCallback;
 import org.springframework.batch.repeat.RepeatContext;
 import org.springframework.batch.repeat.RepeatOperations;
 import org.springframework.batch.repeat.RepeatStatus;
+import org.springframework.lang.Nullable;
 
 /**
  * Simple implementation of the ChunkProvider interface that does basic chunk
@@ -35,6 +36,7 @@ import org.springframework.batch.repeat.RepeatStatus;
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  * @see ChunkOrientedTasklet
  */
 public class SimpleChunkProvider<I> implements ChunkProvider<I> {
@@ -82,9 +84,10 @@ public class SimpleChunkProvider<I> implements ChunkProvider<I> {
 
 	/**
 	 * Surrounds the read call with listener callbacks.
-	 * @return item
+	 * @return the item or {@code null} if the data source is exhausted
 	 * @throws Exception is thrown if error occurs during read.
 	 */
+	@Nullable
 	protected final I doRead() throws Exception {
 		try {
 			listener.beforeRead();
@@ -146,13 +149,14 @@ public class SimpleChunkProvider<I> implements ChunkProvider<I> {
 	 *
 	 * @param contribution the current step execution contribution
 	 * @param chunk the current chunk
-	 * @return a new item for processing
+	 * @return a new item for processing or {@code null} if the data source is exhausted
 	 *
 	 * @throws SkipOverflowException if specifically the chunk is accumulating
 	 * too much data (e.g. skips) and it wants to force a commit.
 	 *
 	 * @throws Exception if there is a generic issue
 	 */
+	@Nullable
 	protected I read(StepContribution contribution, Chunk<I> chunk) throws SkipOverflowException, Exception {
 		return doRead();
 	}

spring-batch-core/src/main/java/org/springframework/batch/core/step/item/SkipWrapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,10 +16,13 @@
 
 package org.springframework.batch.core.step.item;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Wrapper for an item and its exception if it failed processing.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * 
  */
 public class SkipWrapper<T> {
@@ -43,7 +46,7 @@ public class SkipWrapper<T> {
 	}
 
 
-	public SkipWrapper(T item, Throwable e) {
+	public SkipWrapper(T item, @Nullable Throwable e) {
 		this.item = item;
 		this.exception = e;
 	}
@@ -52,6 +55,7 @@ public class SkipWrapper<T> {
 	 * Public getter for the exception.
 	 * @return the exception
 	 */
+	@Nullable
 	public Throwable getException() {
 		return exception;
 	}
@@ -69,4 +73,4 @@ public class SkipWrapper<T> {
 		return String.format("[exception=%s, item=%s]", exception, item);
 	}
 
-}
+}

spring-batch-core/src/main/java/org/springframework/batch/core/step/item/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of step concerns for item-oriented approach.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.item;
+@NonNullApi
+package org.springframework.batch.core.step.item;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/job/package-info.java

@@ -2,5 +2,9 @@
  * {@link org.springframework.batch.core.step.job.JobStep} and related components.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.job;
+@NonNullApi
+package org.springframework.batch.core.step.job;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of step concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step;
+@NonNullApi
+package org.springframework.batch.core.step;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/skip/package-info.java

@@ -2,5 +2,9 @@
  * Specific implementations of skip concerns for items in a step.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.skip;
+@NonNullApi
+package org.springframework.batch.core.step.skip;
+
+import org.springframework.lang.NonNullApi;

spring-batch-core/src/main/java/org/springframework/batch/core/step/tasklet/Tasklet.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,11 +18,13 @@ package org.springframework.batch.core.step.tasklet;
 import org.springframework.batch.core.StepContribution;
 import org.springframework.batch.core.scope.context.ChunkContext;
 import org.springframework.batch.repeat.RepeatStatus;
+import org.springframework.lang.Nullable;
 
 /**
  * Strategy for processing in a step.
  * 
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  * 
  */
 public interface Tasklet {
@@ -38,10 +40,11 @@ public interface Tasklet {
 	 * @param chunkContext attributes shared between invocations but not between
 	 * restarts
 	 * @return an {@link RepeatStatus} indicating whether processing is
-	 * continuable.
+	 * continuable. Returning {@code null} is interpreted as {@link RepeatStatus#FINISHED}
 	 *
 	 * @throws Exception thrown if error occurs during execution.
 	 */
+	@Nullable
 	RepeatStatus execute(StepContribution contribution, ChunkContext chunkContext) throws Exception;
 
 }

spring-batch-core/src/main/java/org/springframework/batch/core/step/tasklet/package-info.java

@@ -2,5 +2,9 @@
  * Interfaces and generic implementations of tasklet concerns.
  *
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  */
-package org.springframework.batch.core.step.tasklet;
+@NonNullApi
+package org.springframework.batch.core.step.tasklet;
+
+import org.springframework.lang.NonNullApi;