在线上环境中，应用可能因为一些异常而终止，我们如果需要及时找到原因，根据 exit code 来定位，是个很好的途径。 spring boot 为开发者提供了相关的接口，方便开发者通过异常类型来定义自己的 exit code：ExitCodeGenerator 和 ExitCodeExceptionMapper.

1. ExitCodeGenerator:

用于主动退出应用，在 SpringApplication.exit(org.springframework.context.ApplicationContext,ExitCodeGenerator..)中用到，该方法会寻找所有的 ExitCodeGenerator 的 Bean, 也会用到方法中的入参对象。

ExitCodeGenerator 声明如下：

@FunctionalInterface
public interface ExitCodeGenerator {/*** Returns the exit code that should be returned from the application.* @return the exit code.*/int getExitCode();}复制代码

1.1 使用:

System.exit(SpringApplication.exit(SpringApplication.run(DemoApplication.class, args)));

@SpringBootApplication
public class DemoApplication{@Beanpublic ExitCoder getTestExitCoder(){return new ExitCoder();}@Beanpublic ExitCoder1 getTestExitCoder1(){return new ExitCoder1();}public static void main(String[] args) {System.exit(SpringApplication.exit(SpringApplication.run(DemoApplication.class, args)));}
}
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import org.springframework.boot.ExitCodeGenerator;public class ExitCoder implements ExitCodeGenerator {@Overridepublic int getExitCode() {System.out.println("get exit code from class: ExitCoder");return 222;}
}
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import org.springframework.boot.ExitCodeGenerator;public class ExitCoder1 implements ExitCodeGenerator {@Overridepublic int getExitCode() {System.out.println("get exit code from class: ExitCoder1");return 221;}
}
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输出为

2019-03-21 21:52:55.802  INFO 44627 --- [           main] com.example.exitcode.DemoApplication     : Starting DemoApplication on lei.local with PID 44627 (/Users/lei/own/projects/java_learning/spring_boot_learning/blog/5exitcode/exitcode/out/production/classes started by lei in /Users/lei/own/projects/java_learning/spring_boot_learning/blog/5exitcode/exitcode)
2019-03-21 21:52:55.806  INFO 44627 --- [           main] com.example.exitcode.DemoApplication     : No active profile set, falling back to default profiles: default
2019-03-21 21:52:56.339  INFO 44627 --- [           main] com.example.exitcode.DemoApplication     : Started DemoApplication in 15.901 seconds (JVM running for 21.676)
get exit code from class: ExitCoder
get exit code from class: ExitCoder1
Disconnected from the target VM, address: '127.0.0.1:50873', transport: 'socket'Process finished with exit code 222
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从上面可以看到，以 exit code 最大的为最终值。

2. ExitCodeExceptionMapper：

用于应用发生不可调整的异常，导致应用退出的情况。声明如下：

@FunctionalInterface
public interface ExitCodeExceptionMapper {/*** Returns the exit code that should be returned from the application.* @param exception the exception causing the application to exit* @return the exit code or {@code 0}.*/int getExitCode(Throwable exception);}
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2.1 使用方式

通过 Bean 来注册，当应用发生异常时，会调用每个ExitCodeExceptionMapper 的实现类。这里，我们可以根据异常类型来设置自己的 exit code:

@SpringBootApplication
public class DemoApplication{@Beanpublic DemoExitCodeExceptionMapper getExitCodeMapper(){return new DemoExitCodeExceptionMapper();}public static void main(String[] args) {SpringApplication.run(DemoApplication.class, args);}@BeanCommandLineRunner showUsers() {return args -> {throw new Exception("xxxxx");};}
}复制代码

public class DemoExitCodeExceptionMapper implements ExitCodeExceptionMapper{/*** Returns the exit code that should be returned from the application.* @param exception the exception causing the application to exit* @return the exit code or {@code 0}.*/@Overridepublic int getExitCode(Throwable exception){System.out.println("exit cod xxxx" + exception.getMessage());if(exception.getCause().getMessage().equals("sdf")){return 254;}return 243;}
}
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运行输出为：

2019-03-21 22:13:34.261  INFO 45049 --- [           main] com.example.exitcode.DemoApplication     : Started DemoApplication in 15.816 seconds (JVM running for 21.521)
exit cod xxxxFailed to execute CommandLineRunner
2019-03-21 22:13:38.797  INFO 45049 --- [           main] ConditionEvaluationReportLoggingListener : Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-03-21 22:13:38.845 ERROR 45049 --- [           main] o.s.boot.SpringApplication               : Application run failedjava.lang.IllegalStateException: Failed to execute CommandLineRunnerat org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:816) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:797) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:324) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]at com.example.exitcode.DemoApplication.main(DemoApplication.java:31) [classes/:na]
Caused by: java.lang.Exception: xxxxxat com.example.exitcode.DemoApplication.lambda$showUsers$0(DemoApplication.java:37) [classes/:na]at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:813) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]... 5 common frames omittedDisconnected from the target VM, address: '127.0.0.1:51237', transport: 'socket'Process finished with exit code 243复制代码

3. 取值逻辑

public int getExitCode() {int exitCode = 0;for (ExitCodeGenerator generator : this.generators) {try {int value = generator.getExitCode();if (value > 0 && value > exitCode || value < 0 && value < exitCode) {exitCode = value;}}catch (Exception ex) {exitCode = (exitCode != 0) ? exitCode : 1;ex.printStackTrace();}}return exitCode;
}
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1. 第一个: 直接取第一个的值。
2. 2....n-1,n: n 和n-1 正负不同，取 n, 相同，取绝对值大的。

4.总结：

• 主动调用SpringApplication.exit 方法使用ExitCodeGenerator ,可以通过 Bean注册，也可通过传值。
• 应用异常退出使用 ExitCodeExceptionMapper, 只能通过 Bean 注册使用。
• 取值： 前后正负不同，取最新, 相同，取绝对值大的。