Java并发编程高级篇(九):在线程之行结束后再做些什么

如果我们想要在线程执行结束后做一些事情,比如生成报表,发送通知邮件或者释放一些系统资源,FutureTask类给于我们最好的支持。

想要实现这种控制方式,我们不能直接把Callable对象直接提交到线程执行器中运行,而是要借助FutureTask类,把需要执行的线程类发送给FutureTask对象,然后把FutureTask类发送给执行器去执行。

首先创建线程类,实现Callable接口(不能使用Runnable)。休眠一个随机时间来模拟线程执行过程。

import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;

/**
 * 创建一个雷ExecutableTask实现Callable接口。
 *
 * 延迟一定是坚守执行
 *
 * Created by hadoop on 2016/11/3.
 */
public class ExecutableTask implements Callable {
    private String name;

    public ExecutableTask(String name) {
        this.name = name;
    }

    @Override
    public String call() throws Exception {
        long duration = (long)(Math.random() * 10);

        System.out.printf("Task: %s will delay %d \n", name, duration);

        TimeUnit.SECONDS.sleep(duration);

        return "Hello, I am " + name;
    }

    public String getName() {
        return name;
    }
}

接下来我们继承FutureTask类实现自己的ResultTask类,并重写done方法。在done方法中即可定义任务执行完毕的处理逻辑,在这里我们打印线程的一些状态。

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

/**
 * 创建类ResultTask继承FutureTask类
 *
 * 重写done()方法:打印任务isCancelled()状态还是完成状态。
 *
 * Created by hadoop on 2016/11/3.
 */
public class ResultTask extends FutureTask {
    private String name;

    public ResultTask(Callable callable) {
        super(callable);
        this.name = ((ExecutableTask)callable).getName();
    }

    @Override
    protected void done() {
        if (isCancelled()) {
            System.out.printf("%s: Has been canceled.\n", name);
        } else {
            System.out.printf("%s: Has been finished.\n", name);
        }
    }
}

在主线程类中,我们创建5个线程任务,因为FutureTask实现了Runnable接口,所以可以直接提交到执行器去运行。主线程休眠5s,然后以此取消5个线程。最后打印已经执行完成的任务的信息。

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * Created by hadoop on 2016/11/3.
 *
 * 在任务结束的时候FutureTask类就会调用done()方法。
 *
 * 创建一个实现Callable接口的ExecutableTask类
 * 创建一个阶乘FutureTask类的ResultTask类
 *
 * 然后我们就可以在done方法啊中做出一些资源释放之类的工作了
 *
 */
public class Main {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();

        ResultTask[] tasks = new ResultTask[5];

        for (int i = 0; i < 5; i++) {
            ExecutableTask task = new ExecutableTask("Task" + String.valueOf(i));
            tasks[i] = new ResultTask(task);
            executor.submit(tasks[i]);
        }

        TimeUnit.SECONDS.sleep(5);

        for (int i = 0; i < 5; i++) {
            tasks[i].cancel(true);
        }

        for (int i = 0; i < 5; i++) {
            if (!tasks[i].isCancelled()) {
                System.out.println(tasks[i].get());
            }
        }

        executor.shutdown();
    }
}

控制台中你可以看到,每个线程的休眠时间,以及线程结束时的状态。还有执行完成线程的信息。

Task: Task0 will delay 3 
Task: Task4 will delay 1 
Task: Task3 will delay 5 
Task: Task2 will delay 8 
Task: Task1 will delay 0 
Task1: Has been finished.
Task4: Has been finished.
Task0: Has been finished.
Task2: Has been canceled.
Task3: Has been canceled.
Hello, I am Task0
Hello, I am Task1
Hello, I am Task4

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