Merge pull request #9740 from thombergs:exit-docs-gh5038

* pr/9740:
  Polish "Improve ExitCodeGenerator doc"
  Improve ExitCodeGenerator doc

Author: snicoll

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -336,8 +336,31 @@ callbacks (such as the `DisposableBean` interface, or the `@PreDestroy` annotati
 be used.
 
 In addition, beans may implement the `org.springframework.boot.ExitCodeGenerator`
-interface if they wish to return a specific exit code when the application ends.
+interface if they wish to return a specific exit code when `SpringApplication.exit()`
+is called. This exit code can then be passed to `System.exit()` to return it as a status
+code.
 
+[source,java,indent=0]
+----
+	@SpringBootApplication
+	public class ExitCodeApplication {
+
+		public static void main(String[] args) {
+			System.exit(SpringApplication.exit(
+					SpringApplication.run(ExitCodeApplication.class, args)));
+		}
+
+		@Bean
+		public ExitCodeGenerator exitCodeGenerator(){
+			return () -> 42;
+		}
+
+	}
+----
+
+Also, the `ExitCodeGenerator` interface may be implemented by exceptions. When such an
+exception is encountered, Spring Boot will return the exit code provided by the
+implemented `getExitCode()` method.
 
 
 [[boot-features-application-admin]]

spring-boot/src/main/java/org/springframework/boot/ExitCodeGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -18,8 +18,7 @@
 
 /**
  * Interface used to generate an 'exit code' from a running command line
- * {@link SpringApplication}. Since 1.3.2 this interface can be used on exceptions as well
- * as directly on beans.
+ * {@link SpringApplication}. Can be used on exceptions as well as directly on beans.
  *
  * @author Dave Syer
  * @see SpringApplication#exit(org.springframework.context.ApplicationContext,