线程池（三）：ForkJoinPool

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

public class Test {

    static List<String> urls = new ArrayList<String>() {
        {
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
            add("http://www.baidu.com");
            add("http://www.sina.com");
        }
    };
    // 本质是一个线程池,默认的线程数量:CPU的核数
    static ForkJoinPool forkJoinPool = new ForkJoinPool(3,
            ForkJoinPool.defaultForkJoinWorkerThreadFactory,
            null,
            true);
    public static String doRequest(String url,int index) {
        return index+" test " + url + "\n";
    }

    static class Job extends RecursiveTask<String> {
        List<String> urls;
        int start;
        int end;

        public Job(List<String> urls, int start, int end) {
            this.urls = urls;
            this.start = start;
            this.end = end;
        }

        @Override
        protected String compute() {
            int count = end - start;
            if (count <= 10) {
                String result = "";
                for (int i = start; i < end; i++) {
                    String s = doRequest(urls.get(i),i);
                    result = result + s;
                }
                return result;
            } else {
                int mid = (start + end) / 2;
                Job job1 = new Job(urls, start, mid);
                job1.fork();
                Job job2 = new Job(urls, mid, end);
                job2.fork();

                //固定写法
                String results = "";
                results += job1.join();
                results += job2.join();
                return results;
            }
        }
    }
    public static void main(String[] args) throws ExecutionException, InterruptedException {


        Job job = new Job(urls, 0, urls.size());
        ForkJoinTask<String> forkJoinTask = forkJoinPool.submit(job);
        String s = forkJoinTask.get();
        System.out.println(s);
    }
}

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

public class NumberSum extends RecursiveTask<Long> {
    private Long start;
    private Long end;

    private Long temp = 10000L;

    public NumberSum(Long start, Long end) {
        this.start = start;
        this.end = end;
    }

    //计算方法
    @Override
    protected Long compute() {
        if ((end - start) < temp) {
            Long sum = 0L;
            for (Long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        } else {
            Long result = 0L;
            Long mid = (start + end) / 2;
            NumberSum n1 = new NumberSum(start, mid);
            n1.fork();
            NumberSum n2 = new NumberSum(mid + 1, end);
            n2.fork();
            result += n1.join();
            result += n2.join();
            return result;
        }
    }

    static ForkJoinPool forkJoinPool = new ForkJoinPool(3,
            ForkJoinPool.defaultForkJoinWorkerThreadFactory,
            null,
            true);

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        NumberSum numberSum = new NumberSum(0L, 1_0000_0000L);
        ForkJoinTask<Long> future = forkJoinPool.submit(numberSum);
        System.out.println(future.get());
    }
}