Part 5: java.util.concurrent - Submit Callable< T > via ExecutorService

Future<T> submit(Callable<T> c)
Today in next part of the series we will talk about submission of callable task via executor service.

As per JAVA version 6.0, ExecutorService Inte易做图ce has following method -
Future< T >  submit( callable c )
Submits a Callable task for execution and returns a Future representing that task computation.
Future< T > will return T on successful completion of the process, otherwise result will not be T.
Lets start with Callable task - As we  know that Callable<T> inte易做图ce has following method - public T call()
So when we say - ExecutorService.submit(Callable Task) --> It starts a new stack starting with call method of callable task, as call method can return T so does future object. Due to this reason the signature of submit(Callable c) is Future< T >.
T --> means anything that extends Object.
package com.jovialjava.blog.threads;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class CallableExample {

    private static final ExecutorService executorPool=Executors.newFixedThreadPool(2);
   
    public static void main(String[] args) {
        CallableTask_1 task_1 = new CallableTask_1();
        CallableTask_2 task_2 = new CallableTask_2();
       
        /**
         * Submit the first task
         */
        Future<Boolean> fut_1 = executorPool.submit(task_1);
        Future<Boolean> fut_2 = executorPool.submit(task_2);
       
        try{
            if(fut_1.get()){
                System.out.println("TASK 1 completed SUCCESSFULLY");
            }
            if(fut_2.get()){
                System.out.println("TASK 2 completed SUCCESSFULLY");
            }
        }catch(ExecutionException e){           
            System.out.println(e.getMessage());
        }catch(InterruptedException e){
            System.out.println(e.getMessage());
        }finally{
            /**====VERY IMPORTANT===
             * This is required to stop the executor pool to
             * stop accepting new request.
             */
            executorPool.shutdown();
        }

    }

   
    /**
     * This task will complete successfully
     */
    public static class CallableTask_1 implements Callable<Boolean>{
        public Boolean call()throws NullPointerException{
            System.out.println("Hi, Inside Callable Task 1");
            return true;
        }       

    }
   
    /**
     * This task will result in error.
     */
    public static class CallableTask_2 implements Callable<Boolean>{
        public Boolean call()throws NullPointerException{
            System.out.println("Hi, Inside Callable Task 2");
            throw new IllegalStateException("Callable Task Exception");
        }       

    }
}

补充：软件开发 , Java ,

上一个：Part 6: java.util.concurrent - Lock and Condition Object
下一个：Part 4: java.util.concurrent - Submit Runnable via ExecutorService