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<String>接口。
*
* 延迟一定是坚守执行
*
* Created by hadoop on 2016/11/3.
*/
public class ExecutableTask implements Callable<String> {
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<String>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<String> {
private String name;
public ResultTask(Callable<String> 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
