详解JDK中ExecutorService与Callable和Future对线程的支持
1、代码背景：
假如有Thread1、Thread2、Thread3、Thread4四条线程分别统计C、D、E、F四个盘的大小，所有线程都统计完毕交给Thread5线程去做汇总，应当如何实现？
2、代码：
统计“盘子”大小的代码，此处实现jdk中的Callable接口，
package com.wang.test.concurrent;
import java.util.concurrent.Callable;
public class Task1 implements Callable<Integer> {
private int x;
private int y;
public Task1(int x, int y) {
this.x = x;
this.y = y;
}
@Override
public Integer call() throws Exception {
return x*y;
}
}
统计汇总的代码，也是实现jdk中的Callable接口，
package com.wang.test.concurrent;
import java.util.concurrent.Callable;
public class Task2 implements Callable<Integer> {
private int x;
private int y;
private int q;
private int w;
public Task2(int x, int y, int q, int w) {
this.x = x;
this.y = y;
this.q = q;
this.w = w;
}
@Override
public Integer call() throws Exception {
return x + y + q + w;
}
}
客户端：使用JDK中Executors.newFixedThreadPool方法创建ExecutorService，ExecutorService的submit方法接收Callable接口的实现，JDK内部将弄成线程处理，使用Future接收submit方法的返回值，当future调用get方法时，如果线程还没有执行完，程序阻塞在这里，知道线程执行完。
package com.wang.test.concurrent;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class Client {
public static void main(String[] args) throws Exception {
ExecutorService pool = Executors.newFixedThreadPool(4);
Task1 t1 = new Task1(1,2);
Task1 t2 = new Task1(23,34);
Task1 t3 = new Task1(23,456);
Task1 t4 = new Task1(3,33);
Future<Integer> f1 = pool.submit(t1);
Future<Integer> f2 = pool.submit(t2);
Future<Integer> f3 = pool.submit(t3);
Future<Integer> f4 = pool.submit(t4);
//Future调用get方法时，如果线程还没有执行完，程序阻塞在这里
Task2 t5 = new Task2(f1.get(), f2.get(), f3.get(), f4.get());
Future<Integer> f5 = pool.submit(t5);
System.out.println(f5.get());
pool.shutdown();
}
}
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