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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();
}
1.1 使用:
System.exit(SpringApplication.exit(SpringApplication.run(DemoApplication.class, args)));
@SpringBootApplication
public class DemoApplication{
@Bean
public ExitCoder getTestExitCoder(){
return new ExitCoder();
}
@Bean
public ExitCoder1 getTestExitCoder1(){
return new ExitCoder1();
}
public static void main(String[] args) {
System.exit(SpringApplication.exit(SpringApplication.run(DemoApplication.class, args)));
}
}
import org.springframework.boot.ExitCodeGenerator;
public class ExitCoder implements ExitCodeGenerator {
@Override
public int getExitCode() {
System.out.println(“get exit code from class: ExitCoder”);
return 222;
}
}
import org.springframework.boot.ExitCodeGenerator;
public class ExitCoder1 implements ExitCodeGenerator {
@Override
public int getExitCode() {
System.out.println(“get exit code from class: ExitCoder1”);
return 221;
}
}
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
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);
}
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{
@Bean
public DemoExitCodeExceptionMapper getExitCodeMapper(){
return new DemoExitCodeExceptionMapper();
}
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Bean
CommandLineRunner showUsers() {
return args -> {throw new Exception(“xxxxx”);};
}
}
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}.
*/
@Override
public int getExitCode(Throwable exception){
System.out.println(“exit cod xxxx” + exception.getMessage());
if(exception.getCause().getMessage().equals(“sdf”)){
return 254;
}
return 243;
}
}
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 failed
java.lang.IllegalStateException: Failed to execute CommandLineRunner
at 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: xxxxx
at 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 omitted
Disconnected from the target VM, address: ‘127.0.0.1:51237’, transport: ‘socket’
Process finished with exit code 243
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;
}
第一个: 直接取第一个的值。
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。
