Java中获得线程的返回值

Java5新增了Callable接口获得线程的返回值，用法如下

package com.ronniewang;


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 GetReturnValueFromCallable {


    private static final int SLEEP_MILLS = 3000;


    private static final int SECOND_MILLS = 1000;


    private static int sleepSeconds = SLEEP_MILLS / SECOND_MILLS;


    ExecutorService executorService = Executors.newCachedThreadPool();


    /**
     * 在创建多线程程序的时候，我们常实现Runnable接口，Runnable没有返回值，要想获得返回值，Java5提供了一个新的接口Callable
     */
    public static void main(String[] args) {


        new GetReturnValueFromCallable().testCallable();
    }


    private void testCallable() {


        /**
         * Callable需要实现的是call()方法，而不是run()方法，返回值的类型有Callable的类型参数指定，
         * Callable只能由ExecutorService.submit() 执行，正常结束后将返回一个future对象
         */
        Future<String> future = executorService.submit(new Callable<String>() {


            public String call() throws Exception {


                Thread.sleep(SLEEP_MILLS);
                return "I from callable";
            }
        });


        while (true) {
            /**
             * 获得future对象之前可以使用isDone()方法检测future是否完成，完成后可以调用get()方法获得future的值，
             * 如果直接调用get()方法，get()方法将阻塞值线程结束
             */
            if (future.isDone()) {
                try {
                    System.out.println(future.get());
                    break;
                } catch (InterruptedException e) {
                    // ignored
                } catch (ExecutionException e) {
                    // ignored
                }
            }
            else {
                try {
                    System.out.println("after " + sleepSeconds-- + " seconds, we will get future");
                    Thread.sleep(SECOND_MILLS);
                } catch (InterruptedException e) {
                    // ignored
                }
            }
        }
    }
}

after 3 seconds, we will get future
after 2 seconds, we will get future
after 1 seconds, we will get future
I from callable

Java中获得线程的返回值

原文：http://blog.csdn.net/ro_wsy/article/details/44566589