Add default methods in listener interfaces

Resolves #3924

Author: parikshitdutta

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2018 the original author or authors.
+ * Copyright 2006-2021 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.
@@ -25,7 +25,7 @@
  * @author Lucas Ward
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
- *
+ * @author Parikshit Dutta
  */
 public interface ChunkListener extends StepListener {
 
@@ -36,14 +36,16 @@ public interface ChunkListener extends StepListener {
 	 *
 	 * @param context The current {@link ChunkContext}
 	 */
-	void beforeChunk(ChunkContext context);
+	default void beforeChunk(ChunkContext context) {
+	}
 
 	/**
 	 * Callback after the chunk is executed, outside the transaction.
 	 *
 	 * @param context The current {@link ChunkContext}
 	 */
-	void afterChunk(ChunkContext context);
+	default void afterChunk(ChunkContext context) {
+	}
 
 	/**
 	 * Callback after a chunk has been marked for rollback.  It is invoked
@@ -57,5 +59,6 @@ public interface ChunkListener extends StepListener {
 	 * @param context the chunk context containing the exception that caused
 	 * the underlying rollback.
 	 */
-	void afterChunkError(ChunkContext context);
+	default void afterChunkError(ChunkContext context) {
+	}
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2021 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.
@@ -22,7 +22,7 @@
  * instances themselves are not used by more than one thread.
  *
  * @author Dave Syer
- *
+ * @author Parikshit Dutta
  */
 public interface JobExecutionListener {
 
@@ -31,7 +31,8 @@ public interface JobExecutionListener {
 	 *
 	 * @param jobExecution the current {@link JobExecution}
 	 */
-	void beforeJob(JobExecution jobExecution);
+	default void beforeJob(JobExecution jobExecution) {
+	}
 
 	/**
 	 * Callback after completion of a job. Called after both both successful and
@@ -40,6 +41,7 @@ public interface JobExecutionListener {
 	 *
 	 * @param jobExecution the current {@link JobExecution}
 	 */
-	void afterJob(JobExecution jobExecution);
+	default void afterJob(JobExecution jobExecution) {
+	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2018 the original author or authors.
+ * Copyright 2006-2021 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.
@@ -23,7 +23,7 @@
  * @author Lucas Ward
  * @author Dave Syer
  * @author Mahmoud Ben Hassine
- *
+ * @author Parikshit Dutta
  */
 public interface StepExecutionListener extends StepListener {
 
@@ -33,7 +33,8 @@ public interface StepExecutionListener extends StepListener {
 	 *
 	 * @param stepExecution instance of {@link StepExecution}.
 	 */
-	void beforeStep(StepExecution stepExecution);
+	default void beforeStep(StepExecution stepExecution) {
+	}
 
 	/**
 	 * Give a listener a chance to modify the exit status from a step. The value
@@ -49,5 +50,7 @@ public interface StepExecutionListener extends StepListener {
 	 * {@code null} to leave the old value unchanged.
 	 */
 	@Nullable
-	ExitStatus afterStep(StepExecution stepExecution);
+	default ExitStatus afterStep(StepExecution stepExecution) {
+		return null;
+	}
 }