Fix compiler warnings

- Add `@Nullable` where needed
- Suppress warnings where appropriate
- Add generic type definitions

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.data.mongodb.core.query.Criteria;
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.lang.Nullable;
 import org.springframework.transaction.support.TransactionSynchronization;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
 import org.springframework.util.Assert;
@@ -113,6 +114,7 @@ public class MongoItemWriter<T> implements ItemWriter<T>, InitializingBean {
 	 *
 	 * @see org.springframework.batch.item.ItemWriter#write(Chunk)
 	 */
+	@SuppressWarnings(value = { "unchecked", "rawtypes" })
 	@Override
 	public void write(Chunk<? extends T> chunk) throws Exception {
 		if (!transactionActive()) {
@@ -184,6 +186,8 @@ public class MongoItemWriter<T> implements ItemWriter<T>, InitializingBean {
 		return TransactionSynchronizationManager.isActualTransactionActive();
 	}
 
+	@SuppressWarnings("unchecked")
+	@Nullable
 	private Chunk<T> getCurrentBuffer() {
 		if (!TransactionSynchronizationManager.hasResource(bufferKey)) {
 			TransactionSynchronizationManager.bindResource(bufferKey, new Chunk<T>());

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/builder/RepositoryItemWriterBuilder.java

@@ -99,6 +99,7 @@ public class RepositoryItemWriterBuilder<T> {
 	 * Builds the {@link RepositoryItemWriter}.
 	 * @return a {@link RepositoryItemWriter}
 	 */
+	@SuppressWarnings("unchecked")
 	public RepositoryItemWriter<T> build() {
 		if (this.repositoryMethodReference != null) {
 			this.methodName = this.repositoryMethodReference.getMethodName();

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilder.java

@@ -91,7 +91,7 @@ public class FlatFileItemReaderBuilder<T> {
 
 	private FixedLengthBuilder<T> fixedLengthBuilder;
 
-	private Class<? extends T> targetType;
+	private Class<T> targetType;
 
 	private String prototypeBeanName;
 
@@ -339,7 +339,7 @@ public class FlatFileItemReaderBuilder<T> {
 	 * @return The current instance of the builder.
 	 * @see BeanWrapperFieldSetMapper#setTargetType(Class)
 	 */
-	public FlatFileItemReaderBuilder<T> targetType(Class<? extends T> targetType) {
+	public FlatFileItemReaderBuilder<T> targetType(Class<T> targetType) {
 		this.targetType = targetType;
 		return this;
 	}
@@ -461,7 +461,7 @@ public class FlatFileItemReaderBuilder<T> {
 
 			if (this.targetType != null || StringUtils.hasText(this.prototypeBeanName)) {
 				if (this.targetType != null && this.targetType.isRecord()) {
-					RecordFieldSetMapper<T> mapper = new RecordFieldSetMapper(this.targetType);
+					RecordFieldSetMapper<T> mapper = new RecordFieldSetMapper<>(this.targetType);
 					lineMapper.setFieldSetMapper(mapper);
 				}
 				else {

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/KafkaItemReader.java

@@ -163,6 +163,7 @@ public class KafkaItemReader<K, V> extends AbstractItemStreamItemReader<V> {
 		this.partitionOffsets = partitionOffsets;
 	}
 
+	@SuppressWarnings("unchecked")
 	@Override
 	public void open(ExecutionContext executionContext) {
 		this.kafkaConsumer = new KafkaConsumer<>(this.consumerProperties);