Java多线程异常处理

线程异常处理

Java中每个线程的异常处理是相互独立的，一个线程产生的异常不会影响其他线程的正常运行。因此，也不能在一个线程中catch另一个线程中抛出的异常。
例如，下面这段代码试图catch方法exceptionInThread()中的异常

 public static void main(String[] args) {
        try{
            exceptionInThread();
        } catch (Exception e) {
            System.out.println("catch exception in the main thread");
        }
    }

    public static void exceptionInThread() {
        Thread t = new Thread(() -> {
            throw new RuntimeException("something wrong in thread");
        });
        t.start();
    }

但如下实际的运行结果可以发现异常并没有被catch住。

线程异常
在Java中可以通过设置Thread.UncaughtExceptionHandler处理线程中的异常。例如下面的代码段中设置了线程的默认UncaughtExceptionHandler.

private static Thread.UncaughtExceptionHandler uncaughtExceptionHandler = (Thread t, Throwable e) -> {
        StringBuilder sb = new StringBuilder();
        sb.append("Thread name: ")
                .append(t.getName())
                .append(", caught exception: ")
                .append(e.getClass())
                .append(" [")
                .append(e.getMessage())
                .append("]");
        System.out.println(sb.toString());
    };

    public static void main(String[] args) {
        Thread.setDefaultUncaughtExceptionHandler(uncaughtExceptionHandler);
        try{
            exceptionInThread();
        } catch (Exception e) {
            System.out.println("catch exception in the main thread");
        }
    }

    public static void exceptionInThread() {
        Thread t = new Thread(() -> {
            throw new RuntimeException("something wrong in thread");
        });
        t.start();
    }

运行结果为：

Thread.UncaughtExceptionHandler

线程池异常处理

Thread.setDefaultUncaughtExceptionHandler(uncaughtExceptionHandler);对线程池中抛出的异常也有同样的效果。
完整代码段如下所示：

package examples;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MultilThreadExceptionHandler {
    private static Thread.UncaughtExceptionHandler uncaughtExceptionHandler = (Thread t, Throwable e) -> {
        StringBuilder sb = new StringBuilder();
        sb.append("Thread name: ")
                .append(t.getName())
                .append(", caught exception: ")
                .append(e.getClass())
                .append(" [")
                .append(e.getMessage())
                .append("]");
        System.out.println(sb.toString());
    };

    public static void main(String[] args) {
        Thread.setDefaultUncaughtExceptionHandler(uncaughtExceptionHandler);
        exceptionInThreadPool();
        exceptionInThread();
    }

    public static void exceptionInThread() {
        Thread t = new Thread(() -> {
            throw new RuntimeException("something wrong in thread");
        });

        t.start();
    }

    public static void exceptionInThreadPool() {
        ExecutorService threadPool = Executors.newFixedThreadPool(1 );

        threadPool.execute(() -> {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            throw new RuntimeException("exception in runnable");
        });
        threadPool.shutdown();
    }

}

TODO

在测试过程中发现，线程池中task通过threadPool.execute提交的runnable中的异常可以被UncaughtExceptionHandler正确处理，但通过threadPool.submit提交的callable中的异常却无法处理。需要进一步阅读源码了解其中机制。