4.6 在一个执行器中删除一个任务

    当你使用Executor时，你没有必要管理线程，因为它已经帮我们管理了线程。你仅仅需要实现Runnable或者Callable任务并发送它们给这个执行器executor。这个executor负责在线程池中创建、管理线程，并且如果它们不需要了，直接结束这些线程。有时，你可能想去删除一个你已经发送给executor的任务。这种情况，你直接调用Future对象的cancel（）方法就可以了，它实现就得就是删除操作。请看下面的这个实例。

 importjava.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
importjava.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
 
public class Task implements Callable<String>{
 
    /**
     * Main method of the task. It has an infiniteloop that writes a message to
     * the console every 100 milliseconds
     */
    @Override
    public String call() throws Exception {
        while (true){
            System.out.printf("Task: Test\n");
            Thread.sleep(100);
        }
    }
    /**
     * @param args
     */
    public staticvoidmain(String[] args) {
        // Create an executor
                ThreadPoolExecutorexecutor=(ThreadPoolExecutor)Executors.newCachedThreadPool();
               
                // Create a task
                Task task=new Task();
               
                System.out.printf("Main: Executing the Task\n");
 
                // Send the task to the executor
                Future<String>result=executor.submit(task);
               
                // Sleep during two seconds
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
               
                // Cancel the task, finishing its execution
                System.out.printf("Main: Cancelling the Task\n");
                result.cancel(true);
                // Verify that the task has been cancelled
                System.out.printf("Main: Cancelled: %s\n",result.isCancelled());
                System.out.printf("Main: Done: %s\n",result.isDone());
               
                // Shutdown the executor
                executor.shutdown();
                System.out.printf("Main: The executor has finished\n");
        }
 
 
}

运行结果：

Main:Executing the Task
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Task:Test
Main:Cancelling the Task
Main:Cancelled: true
Main:Done: true
Main: The executor has finished

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Java并发编程之线程管理（Executor框架16）