Merge pull request #30705 from dugenkui03

* gh-30705:
  Polish "Make event handling in JobExecutionExitCodeGenerator thread-safe"
  Make event handling in JobExecutionExitCodeGenerator thread-safe

Closes gh-30705

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/batch/JobExecutionExitCodeGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -16,8 +16,8 @@
 
 package org.springframework.boot.autoconfigure.batch;
 
-import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.springframework.batch.core.JobExecution;
 import org.springframework.boot.ExitCodeGenerator;
@@ -31,7 +31,7 @@ import org.springframework.context.ApplicationListener;
  */
 public class JobExecutionExitCodeGenerator implements ApplicationListener<JobExecutionEvent>, ExitCodeGenerator {
 
-	private final List<JobExecution> executions = new ArrayList<>();
+	private final List<JobExecution> executions = new CopyOnWriteArrayList<>();
 
 	@Override
 	public void onApplicationEvent(JobExecutionEvent event) {