Update docs with expected behaviour in regards to skippable exceptions

Before this commit, the expected behaviour when a skippbale exception
occurs in a fault tolerant chunk-oriented step was not documented in
details.

This commit update the docs and adds a sample for each case (when a
skippable exception occurs during read, process and write).

Resolves BATCH-2541

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2018 the original author or authors.
+ * Copyright 2006-2019 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.
@@ -344,7 +344,10 @@ public class FaultTolerantStepBuilder<I, O> extends SimpleStepBuilder<I, O> {
 	}
 
 	/**
-	 * Explicitly request certain exceptions (and subclasses) to be skipped.
+	 * Explicitly request certain exceptions (and subclasses) to be skipped. These
+	 * exceptions (and their subclasses) might be thrown during any phase of the chunk
+	 * processing (read, process, write) but separate counts are made of skips on
+	 * read, process and write inside the step execution.
 	 *
 	 * @param type the exception type.
 	 * @return this for fluent chaining

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2019 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 @@ package org.springframework.batch.core.step.skip;
  * 
  * @author Lucas Ward
  * @author Dave Syer
+ * @author Mahmoud Ben Hassine
  */
 public interface SkipPolicy {
 
@@ -31,7 +32,7 @@ public interface SkipPolicy {
 	 * {@code skipCount<0}. Implementations should avoid throwing any
 	 * undeclared exceptions.
 	 * 
-	 * @param t exception encountered while reading
+	 * @param t exception encountered while processing
 	 * @param skipCount currently running count of skips
 	 * @return true if processing should continue, false otherwise.
 	 * @throws SkipLimitExceededException if a limit is breached

spring-batch-core/src/main/resources/org/springframework/batch/core/configuration/xml/spring-batch-3.0.xsd

@@ -841,6 +841,9 @@
 					are declared as included take precedence over the same value if it is also excluded.
 					Exceptions that are already marked as no-rollback
 					are automatically skippable (but it doesn't hurt to add them again here).
+					Exceptions (and their subclasses) that are declared might be thrown
+					during any phase of the chunk processing (read, process, write) but separate counts
+					are made of skips on read, process and write inside the step execution.
 					]]>
 					</xsd:documentation>
 				</xsd:annotation>