Notify the calling method about the exception occured in thread

Question

I am writing an Spring-mvc application.

I am executing task using ThreadPoolTaskExecutor.

I have below sample code.

MyClass.java

public class MyClass {
    public void startProcess() {
        ThreadPoolTaskExecutor taskExecutor = //Initializing 
        for (int i = 1; i <= 5; i++) {
            taskExecutor.execute(new MyRunnable());
            // I can call taskExecutor.submit(task); also, if required
        }
    }
}

MyRunnable.java

public class MyRunnable implements Runnable {

    @Override
    public void onRun() {
        try {
            //Code which generates exception like below
            throw new Exception("Runtime Exception");
        } catch (Exception e1) {
            // log or throw the exception
        }
    }
}

I want to notify startProcess() about the exception occurred in MyRunnable's run method.

Can any one please guide me for this.

I found below links but it is not solving my problem.

• Handling exceptions from Java ExecutorService tasks
• http://java.dzone.com/articles/spring-async-and-exception

Thanks.

Edit:

One more question. If I am using @Async for asynchronous call to my some other method and If I want to check for the exception occured in async method then what should I do? As async method also returns future object.

Answer for @Async question I got from here

Answer 1

You can add constructor with some listener to your Thread.

Like:

ExceptionListener:

  public class ExceptionListener{
    public void doSomething(long threadId,Exception e){
      //...e.g., notify startProcess()
    }
  }

MyRunnable:

  public class MyRunnable implements Runnable {
    private ExceptionListener listener;

    private MyRunnable(ExceptionListener exception) {
      this.listener = listener;
    }

    @Override
    public void run() {
      //...
      listener.doSomething(Thread.currentThread().getId(),new Exception("Runtime Exception"));
      //...
    }
  }

startProcess():

  public void startProcess() {
    ThreadPoolTaskExecutor taskExecutor = //Initializing 
    ExceptionListener listener= new ExceptionListener();
    for (int i = 1; i <= 5; i++) {
        taskExecutor.execute(new MyRunnable(listener();
        // I can call taskExecutor.submit(task); also, if required
    }
  }

Or, you can use Thread.UncaughtExceptionHandler, like described here.

edited.

Clarification:

if exception occurs, I have to stop my further execution of other processes. So I want to catch or get notified about the exception in startProcess method. – Naman Gala 1 hour ago

Answer:

I suppose that your worker thread will have while cycle. So you can just pass volatile boolean to each thread and set it up to true or false in case of exception, cycle condition will be this boolean variable. – Maksym 58 mins ago

Answer 2

Instead of Runnable, implement Callable. A Callable can throw an exception, and when you retrieve the result of the Callable using a Future, you will get the exception thrown as an ExecutionException:

public class MyCallable implements Callable<Void> {
    public Void call() throws Exception {
        try {
            //Code which generates exception like below
            throw new Exception("Runtime Exception");
        } catch (Exception e1) {
            // log or throw the exception
        }
        return null; // To satisfy the method signature
    }
}

In MyClass:

List<Future<Void>> futures = new ArrayList<>();
for (int i = 1; i <= 5; i++) {
    Future<Void> future = taskExecutor.submit(new MyCallable());
    futures.add(future);
}

// After all tasks have started, now wait for all of them to complete (they run in parallel)
// and check if there were any exceptions

for (Future<Void> future : futures) {
    try {
        future.get();
    } catch (ExecutionException e) {
        // Access the exception thrown by the different thread.
        e.getCause().printStackTrace();
    }
}