FutureTask例子（转）

转自：http://programmingexamples.wikidot.com/futuretask

A cancellable asynchronous computation. This class provides a base implementation of Future, with methods to start and cancel a computation, query to see if the computation is complete, and retrieve the result of the computation. The result can only be retrieved when the computation has completed; the get method will block if the computation has not yet completed. Once the computation has completed, the computation cannot be restarted or cancelled.[1]

The following example illustrates the use of the Futuretask together with the Callable.
It reverses the submitted string slowly at a rate of one char per second. In the mean time, the main thread keeps polling to see if the task is completed.

import java.util.concurrent.*;
import java.util.concurrent.ExecutorService;

public class MyStringReverser
{
    ExecutorService executor = Executors.newFixedThreadPool(1);

    SlowStringReverser reverser = new SlowStringReverser();

    void doReverse(final String target) throws InterruptedException
    {

        FutureTask<String> future = new FutureTask<String>(
                new Callable<String>()
                {
                    public String call()
                    {
                        return reverser.reverseString(target);
                    }
                });
        executor.execute(future);

        // try every 10 seconds
        while (!future.isDone())
        {
            System.out.println("Task not yet completed.");
            try
            {
                Thread.sleep(500);
            } catch (InterruptedException ie)
            {
                System.out.println("Will check after 1/2 sec.");
            }
        }
        try
        {
            System.out.println("Here is the result..." + future.get());
        } catch (ExecutionException ex)
        {
        }
        executor.shutdown();
        return;
    }

    public static void main(String args[])
    {
        MyStringReverser msr = new MyStringReverser();
        try
        {
            msr.doReverse("foobar");
        } catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

class SlowStringReverser
{
    StringBuffer orgString;

    StringBuffer reversedString;

    SlowStringReverser(String orgStr)
    {
        orgString = new StringBuffer(orgStr);
    }

    SlowStringReverser()
    {

    }

    public String reverseString(String str)
    {
        orgString = new StringBuffer(str);
        reversedString = new StringBuffer();
        for (int i = (orgString.length() - 1); i >= 0; i--)
        {

            reversedString.append(orgString.charAt(i));
            System.out.println("Reversing one character per second."
                    + reversedString);
            try
            {
                Thread.sleep(1000);
            } catch (InterruptedException ie)
            {
            }
        }
        return reversedString.toString();
    }
}