在Eclipse中抛出未检查的异常时，从新创建的线程打印堆栈跟踪 [英] Printing the stack trace from a newly created thread when an unchecked exception is thrown in Eclipse

问题描述

如果从主线程不同的线程抛出未检查的异常，为什么在Eclipse的控制台中无法看到堆栈跟踪？例如： p>

  ScheduledThreadPoolExecutor scheduledExecutor; 
 scheduledExecutor.scheduleAtFixedRate（new Log（），0，LOGGING_FREQUENCY_MS，Tim​​eUnit.MILLISECONDS）; 
 public class Log实现Runnable {
 public void run（）{
 //抛出NullPointerException 
} 
} 
  

我没有输出。但是如果我这样做：

  ScheduledThreadPoolExecutor scheduledExecutor; 
 scheduledExecutor.scheduleAtFixedRate（new Log（），0，LOGGING_FREQUENCY_MS，Tim​​eUnit.MILLISECONDS）; 
 public class Log实现Runnable {
 public void run（）{
 try {
 // NullPointerException抛出
} catch（异常e）{
 e.printStackTrace（）; 
} 
} 
} 
  

我可以看到堆栈跟踪

为什么？

编辑：后续问题：打印由线程池线程抛出的异常的最简单的方法？为每一个Runnable添加try-catch当然是非常难看的。

解决方案

因为Executor已经吞没了异常。您可以通过查询返回的未来来查看是否有人：

 未来<？> f = scheduledExecutor.scheduleAtFixedRate（new Log（），...）; 
 try {
 f.get（）; 
} catch（ExecutionException e）{
 Throwable actualException = e.getCause（）; 
} 
  

请注意， f.get（）将阻塞，直到任务被取消或引发异常，所以你可能想在一个单独的线程中调用它。

Why am I unable to see the stack trace in Eclipse's console when an unchecked Exception is thrown from a thread different from the main thread?

For example:

ScheduledThreadPoolExecutor scheduledExecutor;
scheduledExecutor.scheduleAtFixedRate(new Log(), 0, LOGGING_FREQUENCY_MS, TimeUnit.MILLISECONDS);
public class Log implements Runnable {
        public void run() {
     //NullPointerException is thrown
     }
}

I get no output. But if I do:

ScheduledThreadPoolExecutor scheduledExecutor;
scheduledExecutor.scheduleAtFixedRate(new Log(), 0, LOGGING_FREQUENCY_MS, TimeUnit.MILLISECONDS);
public class Log implements Runnable {
        public void run() {
        try {
        //NullPointerException is thrown
        }catch(Exception e){
             e.printStackTrace();
        }
    }
}

I can see the stack trace.

Why?

EDIT: Follow-up question: What would be the easiest way to print the exceptions thrown by thread-pool threads? Adding try-catch to every single Runnable is of course really ugly.

解决方案

Because the Executor has "swallowed" the exception. You can see if you got one by querying the returned future:

Future<?> f = scheduledExecutor.scheduleAtFixedRate(new Log(),...);
try {
    f.get();
} catch (ExecutionException e) {
    Throwable actualException = e.getCause();
}

Note that f.get() will block until the task is cancelled or throws an exception so you will probably want to call it in a separate thread.

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