假设有一个计算量非常大的任务，使用单线程处理会花费很长时间才能处理完成，这时候可以考虑使用多线程分批计算数据，然后再汇总数据输出。在这里，使用了CyclicBarrier来实现。这个类的功能就是指定特定的线程数，等到这些线程都执行完毕之后，才会执行它的await()方法后面的代码，如果在构造器里设定了一个线程类，那么会在业务线程执行完毕之后，先执行构造器里的线程，然后执行await方法后面的线程。

package test;

import java.util.HashMap;

import java.util.Map;

import java.util.concurrent.BrokenBarrierException;

import java.util.concurrent.Callable;

import java.util.concurrent.CyclicBarrier;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Future;

public class Test1 {

private static ExecutorService service = Executors.newFixedThreadPool(4);

public static void main(String[] args) {

final Map map = new HashMap(4);

CyclicBarrier cb = new CyclicBarrier(4, new Runnable(){

public void run() {

Integer count1 = map.get("1");

Integer count2 = map.get("2");

Integer count3 = map.get("3");

Integer count4 = map.get("4");

System.out.println("count= " + (count1 + count2 + count3 + count4));

}

});

new Thread(new TestThread(map, "1", cb,1000)).start();

new Thread(new TestThread(map, "2", cb,1000)).start();

new Thread(new TestThread(map, "3", cb,1000)).start();

new Thread(new TestThread(map, "4", cb,1000)).start();

//线程池实现方式

int sum = 0;

for(int i = 0; i < 4; i++) {

Future data = service.submit(new Callable(){

@Override

public Integer call() throws Exception {

int sum = 0;

for(int i = 0; i < 1000; i++) {

sum += i;

}

return sum;

}

});

try {

sum += data.get().intValue();

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (ExecutionException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

System.out.println("count===" + sum);

}

}

class TestThread implements Runnable {

private Map map;

private String type;

private CyclicBarrier cb;

private int n;

public TestThread(Map map, String type, CyclicBarrier cb, int n) {

this.map = map;

this.type =type;

this.cb = cb;

this.n = n;

}

@Override

public void run() {

int sum = 0;

for(int i = 0; i < n; i++) {

sum += i;

}

map.put(type, sum);

try {

cb.await();

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (BrokenBarrierException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}