我有一个Java main类,在这个类中,我启动一个新线程,在main中,它等待线程死亡。在某个时刻,我从线程抛出运行时异常,但我无法捕获从主类中的线程抛出的异常。

代码如下:

public class Test extends Thread
{
  public static void main(String[] args) throws InterruptedException
  {
    Test t = new Test();

    try
    {
      t.start();
      t.join();
    }
    catch(RuntimeException e)
    {
      System.out.println("** RuntimeException from main");
    }

    System.out.println("Main stoped");
  }

  @Override
  public void run()
  {
    try
    {
      while(true)
      {
        System.out.println("** Started");

        sleep(2000);

        throw new RuntimeException("exception from thread");
      }
    }
    catch (RuntimeException e)
    {
      System.out.println("** RuntimeException from thread");

      throw e;
    } 
    catch (InterruptedException e)
    {

    }
  }
}

有人知道为什么吗?


当前回答

目前您只捕获RuntimeException, Exception的一个子类。但是您的应用程序可能会抛出Exception的其他子类。捕获除RuntimeException之外的泛型异常

由于线程前端已经改变了许多东西,请使用高级java API。

优先选择高级java.util.concurrent API用于多线程,如ExecutorService或ThreadPoolExecutor。

您可以自定义ThreadPoolExecutor来处理异常。

示例来自oracle文档页:

覆盖

protected void afterExecute(Runnable r,
                            Throwable t)

方法,在完成给定可运行对象的执行时调用。此方法由执行任务的线程调用。如果非null,则Throwable是导致执行突然终止的未捕获的RuntimeException或Error。

示例代码:

class ExtendedExecutor extends ThreadPoolExecutor {
   // ...
   protected void afterExecute(Runnable r, Throwable t) {
     super.afterExecute(r, t);
     if (t == null && r instanceof Future<?>) {
       try {
         Object result = ((Future<?>) r).get();
       } catch (CancellationException ce) {
           t = ce;
       } catch (ExecutionException ee) {
           t = ee.getCause();
       } catch (InterruptedException ie) {
           Thread.currentThread().interrupt(); // ignore/reset
       }
     }
     if (t != null)
       System.out.println(t);
   }
 }

用法:

ExtendedExecutor service = new ExtendedExecutor();

我在上面的代码中添加了一个构造函数:

 public ExtendedExecutor() { 
       super(1,5,60,TimeUnit.SECONDS,new ArrayBlockingQueue<Runnable>(100));
   }

您可以更改此构造函数以满足您对线程数量的要求。

ExtendedExecutor service = new ExtendedExecutor();
service.submit(<your Callable or Runnable implementation>);

其他回答

使用Callable而不是Thread,然后你可以调用Future#get(),它会抛出Callable抛出的任何异常。

最有可能的;

您不需要将异常从一个线程传递到另一个线程。 如果你想处理异常,只需在抛出异常的线程中处理即可。 在本例中,主线程不需要从后台线程等待,这实际上意味着您根本不需要后台线程。

但是,让我们假设您确实需要处理来自子线程的异常。我将像这样使用ExecutorService:

ExecutorService executor = Executors.newSingleThreadExecutor();
Future<Void> future = executor.submit(new Callable<Void>() {
    @Override
    public Void call() throws Exception {
        System.out.println("** Started");
        Thread.sleep(2000);
        throw new IllegalStateException("exception from thread");
    }
});
try {
    future.get(); // raises ExecutionException for any uncaught exception in child
} catch (ExecutionException e) {
    System.out.println("** RuntimeException from thread ");
    e.getCause().printStackTrace(System.out);
}
executor.shutdown();
System.out.println("** Main stopped");

打印

** Started
** RuntimeException from thread 
java.lang.IllegalStateException: exception from thread
    at Main$1.call(Main.java:11)
    at Main$1.call(Main.java:6)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
** Main stopped

如果你实现Thread。在启动线程的类UncaughtExceptionHandler中,你可以设置并重新抛出异常:

public final class ThreadStarter implements Thread.UncaughtExceptionHandler{

private volatile Throwable initException;

    public void doSomeInit(){
        Thread t = new Thread(){
            @Override
            public void run() {
              throw new RuntimeException("UNCAUGHT");
            }
        };
        t.setUncaughtExceptionHandler(this);

        t.start();
        t.join();

        if (initException != null){
            throw new RuntimeException(initException);
        }

    }

    @Override
    public void uncaughtException(Thread t, Throwable e) {
        initException =  e;
    }    

}

这将导致以下输出:

Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: UNCAUGHT
    at com.gs.gss.ccsp.enrichments.ThreadStarter.doSomeInit(ThreadStarter.java:24)
    at com.gs.gss.ccsp.enrichments.ThreadStarter.main(ThreadStarter.java:38)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.lang.RuntimeException: UNCAUGHT
    at com.gs.gss.ccsp.enrichments.ThreadStarter$1.run(ThreadStarter.java:15)

对于那些需要停止所有线程运行,并在其中任何一个线程在异常上停止时重新运行所有线程的人:

@Override
public void onApplicationEvent(ContextRefreshedEvent event) {

     // could be any function
     getStockHistory();

}


public void getStockHistory() {

     // fill a list of symbol to be scrapped
     List<String> symbolListNYSE = stockEntityRepository
     .findByExchangeShortNameOnlySymbol(ContextRefreshExecutor.NYSE);


    storeSymbolList(symbolListNYSE, ContextRefreshExecutor.NYSE);

}


private void storeSymbolList(List<String> symbolList, String exchange) {

    int total = symbolList.size();

    // I create a list of Thread 
    List<Thread> listThread = new ArrayList<Thread>();

    // For each 1000 element of my scrapping ticker list I create a new Thread
    for (int i = 0; i <= total; i += 1000) {
        int l = i;

        Thread t1 = new Thread() {

            public void run() {

                // just a service that store in DB my ticker list
                storingService.getAndStoreStockPrice(symbolList, l, 1000, 
                MULTIPLE_STOCK_FILL, exchange);

            }

        };

    Thread.UncaughtExceptionHandler h = new Thread.UncaughtExceptionHandler() {
            public void uncaughtException(Thread thread, Throwable exception) {

                // stop thread if still running
                thread.interrupt();

                // go over every thread running and stop every one of them
                listThread.stream().forEach(tread -> tread.interrupt());

                // relaunch all the Thread via the main function
                getStockHistory();
            }
        };

        t1.start();
        t1.setUncaughtExceptionHandler(h);

        listThread.add(t1);

    }

}

总结如下:

你有一个主函数来创建多个线程,每个线程都有UncaughtExceptionHandler,由线程内的任何异常触发。将每个线程添加到一个列表中。如果一个UncaughtExceptionHandler被触发,它将循环遍历列表,停止每个线程并重新启动主函数重新创建所有线程。

请看看Thread。UncaughtExceptionHandler

更好的(替代)方法是使用Callable和Future来获得相同的结果…