前言

前些天，在网上逛论坛的时候看到 UncaughtExceptionHandler ，貌似从来没用过，所以学习下

一、UncaughtExceptionHandler 是什么？

/*** 当线程由于未捕获异常而突然终止时调用的处理程序接口。 * 当线程由于未捕获异常即将终止时，Java虚拟机将使用getUncaughtExceptionHandler查询线程的* UncaughtExceptionHandler，并调用处理程序的uncaughtException方法，将线程和异常作为参数传递。* 如果线程未显式设置其UncaughtExceptionHandler，则其ThreadGroup对象将充当其* UncaughtExceptionHandler。* 如果ThreadGroup对象对处理异常没有特殊要求，它可以将调用转发给默认的未捕获异常处理程序。*/
public interface UncaughtExceptionHandler {/*** 方法，该方法在给定线程由于给定的未捕获异常而终止时调用。 * Java虚拟机将忽略此方法引发的任何异常。 * 参数： * t–线程 * e–异常*/void uncaughtException(Thread t, Throwable e);}

这个描述看取来就是给程序员一个钩子函数，让程序可以感知到线程非正常关闭时的情况，可以打日志或者啥操作

二、使用步骤

1.通过try-catch捕捉子线程的问题

public class Test {public static void main(String[] args) {try {Thread thread = new Thread(new Task());thread.start();} catch (Exception e) {System.out.println("==Exception: " + e.getMessage());}}
}class Task implements Runnable {@Overridepublic void run() {System.out.println(1 / 0);}
}
输出
Exception in thread "Thread-0" java.lang.ArithmeticException: / by zeroat com.example.demo.config.Task.run(ttt.java:33)at java.lang.Thread.run(Thread.java:745)

可以看到，其实catch 并未捕捉到异常，而子线程的错误抛出到虚拟机了

2.非线程池设置

通过设置线程的UncaughtExceptionHandler 则可以捕捉到异常

public class Test {public static void main(String args[]) {Thread thread = new Thread(new Task());thread.setUncaughtExceptionHandler(new ExceptionHandlerDemo());thread.start();}
}class ExceptionHandlerDemo implements Thread.UncaughtExceptionHandler {@Overridepublic void uncaughtException(Thread t, Throwable e) {System.out.println("whp Exception: " + e.getMessage());}
}class Task implements Runnable {@Overridepublic void run() {System.out.println(1 / 0);}
}输出：
whp Exception: / by zero

3.线程池的情况下设置UncaughtExceptionHandler

public class testClass {public static void main(String[] args) throws ExecutionException, InterruptedException {ThreadPoolTaskExecutor executorService = buildThreadPoolTaskExecutor();//这里注意先是execute ,如果是submit 则有些不同 需要get 才能出现错误executorService.execute(() -> run("execute方法"));}private static void run(String name) {String printStr = "【thread-name:" + Thread.currentThread().getName() + ",执行方式:" + name+"】";System.out.println(printStr);throw new RuntimeException(printStr + ",出现异常");}private static ThreadPoolTaskExecutor buildThreadPoolTaskExecutor() {ThreadPoolTaskExecutor executorService = new ThreadPoolTaskExecutor();executorService.setCorePoolSize(5);executorService.setMaxPoolSize(5);executorService.setQueueCapacity(10);executorService.setKeepAliveSeconds(10);executorService.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());executorService.setThreadFactory(new DefineThreadFactory("小王"));executorService.initialize();return executorService;}}import io.netty.util.concurrent.DefaultThreadFactory;/*** 这里图简单 ，继承了一个ThreadFactory实现*/
public class DefineThreadFactory extends DefaultThreadFactory {public DefineThreadFactory(String poolName) {super(poolName);}@Overridepublic Thread newThread(Runnable r) {Thread t = super.newThread(r);//给生成的线程设置一个错误处理器t.setUncaughtExceptionHandler(new ExceptionHandler());return t;}
}public class ExceptionHandler implements Thread.UncaughtExceptionHandler {@Overridepublic void uncaughtException(Thread t, Throwable e) {System.out.println("define==Exception: " + e.getMessage());}
}
输出：
09:55:09.844 [main] INFO org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor - Initializing ExecutorService
【thread-name:小王-1-1,执行方式:execute方法】
define==Exception: 【thread-name:小王-1-1,执行方式:execute方法】,出现异常