Java并发编程之Future，ExecutorService，Callable讲解实例

并发接口

位置：java/util/concurrent（多线程并发，J.U.C）：
接口：
Callable（类似Runnable）,
Executor（线程池）,
Future(线程执行结果),
FutureTask（线程任务），
Excutors(线程池工厂，可创建ExecutorService)。。。

这里的并发是针对多线程而言的，在java中创建线程有四种方式：
1）继承Thread类
2）实现Runnable接口
3）使用Executor线程池创建
4）实现Callable接口

其中3和4是针对多线程的。

锁接口

位置：java/util/concurrent/locks/（锁相关）
相关接口：
Condition(封装对象object的监视方法如wait，notify等),
Lock,
ReadWriteLock,
ReentrantLock。。。

在没有锁的api之前，锁的实现主要使用synchronized，该关键字利用的是每个对象都有的隐式监视锁。但不够灵活，所以有了新的API。
锁是为了在多个线程同时访问同一共享资源的时候采取的策略，此时只有得到该资源对应唯一锁的线程可以操作资源，其他线程直到占有该锁的线程释放该锁后才可以访问对应资源。
当然，有的锁实现比如读写锁可以允许几个线程同时访问资源，如读取与写入同时进行。

实例

本文将讲解Future，ExecutorService，Callable的使用：

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.*;

public class MyCallable implements Callable<String> {

    @Override
    public String call() throws Exception {
        Thread.sleep(1000);//暂停1s
        return Thread.currentThread().getName();//获取当前线程名称，线程被执行时该方法返回String并封装在Future接口中。
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);//创建大小为10的线程池
        List> list = new ArrayList>();//存储线程处理结果
        Callable callable = new MyCallable();
        for (int i = 0; i < 50; i++) {
            Future future = executorService.submit(callable);//线程池只有10，要执行50个线程，分50/10=5次进行，每进行完10个callable后重新调用call(),因此每执行输出10行就会等1s。
            list.add(future);
        }
        for (Future fut : list) {
            System.out.println(new Date() + "::" + fut.get());
        }

        executorService.shutdown();//别忘了要关闭线程池哦
    }

}

结果如下，从结果也可以看出执行过程并不是同步顺序的：

Sat Feb 17 14:59:47 CST 2018::pool-1-thread-1
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-2
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-3
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-4
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-5
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-6
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-7
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-8
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-9
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-10
Sat Feb 17 14:59:48 CST 2018::pool-1-thread-3
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-4
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-2
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-5
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-1
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-6
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-8
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-7
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-9
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-10
Sat Feb 17 14:59:49 CST 2018::pool-1-thread-9
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-10
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-7
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-8
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-6
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-1
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-5
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-2
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-4
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-3
Sat Feb 17 14:59:50 CST 2018::pool-1-thread-3
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-4
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-2
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-5
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-1
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-6
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-8
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-7
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-10
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-9
Sat Feb 17 14:59:51 CST 2018::pool-1-thread-3
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-4
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-2
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-5
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-1
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-6
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-8
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-7
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-10
Sat Feb 17 14:59:52 CST 2018::pool-1-thread-9

以上就是对Callable和ExecutorService的简单使用，后续会发一些深入的文章。