Exception on running thread

How to catch an exception thrown by run() of a running thread?  

Below line set UncaughtExceptionHandler concrete class to catch Exception. Concrete class include definition of exception handler.

setDefaultUncaughtExceptionHandler is a static method of Thread class.

Thread.setDefaultUncaughtExceptionHandler(new ThreadExceptionHandler());

Interface used

@FunctionalInterface

    public interface UncaughtExceptionHandler {

        /**

         * Method invoked when the given thread terminates due to the

         * given uncaught exception.

         * <p>Any exception thrown by this method will be ignored by the

         * Java Virtual Machine.

         * @param t the thread

         * @param e the exception

         */

        void uncaughtException(Thread t, Throwable e);

    }

Concrete class implementing UncaughtExceptionHandler

import java.lang.Thread.UncaughtExceptionHandler;

/*   Method invoked when the given thread terminates due to the

     given uncaught exception.*/

public class ThreadExceptionHandler implements UncaughtExceptionHandler{

     @Override

     public void uncaughtException(Thread t, Throwable e) {

          System.out.println("Thread " + t.getName() + "Throwable " + e);

          throw new NullPointerException();

     }

}

 ThreadException client class

package com.threadexception;

/* How to catch an exception thrown

 * by run() of a running thread */

public class ThreadException {

   public static void main(String[] args) {

      Thread t1 = new Thread(new Task());

      System.out.println("Thread starts " +

      Thread.currentThread().getName());

      Thread.setDefaultUncaughtExceptionHandler

      (new ThreadExceptionHandler());

      try {

         t1.start();

      } catch (ArithmeticException e) {

         System.out.println("Excption Catch");

      }

      System.out.println("Main Thread Ends");

   }

}

class Task implements Runnable {

   public void run() {

      int a = 10 / 0;

   }

}

Output

Thread starts main

Main Thread Ends

Thread Thread-0Throwable java.lang.ArithmeticException: / by zero

Summary:

     

     a) Ideally one default implementation is giving for system wide if there is any thread which throws any exception and other exception handler for particular threads.

  b)While using executorService.submit() or executorService.execute(), always remember that execute() returns nothing and thus it throws Exception where as submit() returns Future and until we’re not getting future.get(), it doesn’t throw any Exception.

     c) By implementing ThreadFactory, we can rule over threads created by ThreadPool.

Using ThreadFactory

/* An object that creates new threads on demand */

public class SpecialThread implements ThreadFactory {

    

     /* Adding special property to all threads being created

      * No need to set default Exception handler

     */

     public Thread newThread(Runnable r) {

          Thread t = new Thread(r);

          t.setUncaughtExceptionHandler(new ThreadExceptionHandler());

          return t;

     }

}

/* How to catch an exception thrown

 * by run() of a running thread */

public class ThreadException {

     public static void main(String[] args) {

          /* Creating threads which auto-catch the exception*/

          ExecutorService executorService = Executors.

                   newCachedThreadPool(new SpecialThread());

          executorService.execute(new Task());

          executorService.execute(new Task());

          executorService.execute(new Task());

          executorService.shutdown();

     }

}

class Task implements Runnable {

     public void run() {

          int a = 10 / 0;

     }

}