java并发编程核心方法与框架_Java并发编程核心方法与框架-Future和Callable的使用...

Callable接口与Runnable接口对比的主要优点是Callable接口可以通过Future获取返回值。但是Future接口调用get()方法取得结果时是阻塞的，如果调用Future对象的get()方法时任务尚未执行完，则调用get()方法时一直阻塞到此任务完成。如果前面的任务耗时很多，则后面的任务调用get()方法就呈阻塞状态，大大影响运行效率。主线程不能保证首先获得的是最先完成任务的返回值，这是Future的缺点。

public class MyCallable implements Callable {

private int age;

public MyCallable(int age) {

super();

this.age = age;

}

@Override

public String call() throws Exception {

TimeUnit.SECONDS.sleep(8);

return "返回值 年龄是：" + age;

}

public static void main(String[] args) {

MyCallable myCallable = new MyCallable(22);

int corePoolSize = 2;

int maximumPoolSize = 3;

int keepAliveTime = 5;

TimeUnit unit = TimeUnit.SECONDS;

LinkedBlockingDeque workQueue = new LinkedBlockingDeque();

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);

Future future = threadPoolExecutor.submit(myCallable);

try {

System.out.println(System.currentTimeMillis());

String string = future.get();

System.out.println(string);

System.out.println(System.currentTimeMillis());

} catch (Exception e) {

e.printStackTrace();

}

}

}

打印结果如下：

1470904027660

返回值 年龄是：22

1470904035663

从打印结果看，可见get()方法具有阻塞的特性。

方法submit()不仅可以传入Callable对象，还可以传入Runnable对象，submit()方法支持有返回值和无返回值。

public class Run {

public static void main(String[] args) {

try {

Runnable runnable = new Runnable() {

@Override

public void run() {

System.out.println("打印的信息");

}

};

ExecutorService executorService = Executors.newCachedThreadPool();

Future future = executorService.submit(runnable);

System.out.println(future.get() + " " + future.isDone());

} catch (Exception e) {

e.printStackTrace();

}

}

}

打印结果如下：

打印的信息

null true

方法isDone()无阻塞特性。

使用ExecutorService接口中的方法submit(Runnable, T result)

public class User {

private String username;

private String password;

//省略getter setter

}

public class MyRunnable implements Runnable {

private User user;

public MyRunnable(User user) {

super();

this.user = user;

}

@Override

public void run() {

try {

TimeUnit.SECONDS.sleep(2);

} catch (InterruptedException e) {

e.printStackTrace();

}

user.setUsername("admin");

user.setPassword("123456");

}

}

public class Main {

FutureTask task;

public static void main(String[] args) {

try {

User user = new User();

MyRunnable myRunnable = new MyRunnable(user);

int corePoolSize = 10;

int maximumPoolSize = 10;

int keepAliveTime = 10;

TimeUnit unit = TimeUnit.SECONDS;

LinkedBlockingDeque workQueue = new LinkedBlockingDeque<>();

ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);

Future future = executor.submit(myRunnable, user);

System.out.println(System.currentTimeMillis());

System.out.println(user.getUsername() + "-" + user.getPassword());

user = future.get();

System.out.println(user.getUsername() + "-" + user.getPassword());

System.out.println(System.currentTimeMillis());

} catch (Exception e) {

e.printStackTrace();

}

}

}

控制台打印结果如下：

1470908214853

null-null

admin-123456

1470908216855