java多线程之Future和FutureTask使用实例

public interface Callable<V> { /** * Computes a result, or throws an exception if unable to do so. * * @return computed result * @throws Exception if unable to compute a result */ V call() throws Exception; }
public interface Future<V> {
 
  /**
   * Attempts to cancel execution of this task. This attempt will
   * fail if the task has already completed, has already been cancelled,
   * or could not be cancelled for some other reason. If successful,
   * and this task has not started when <tt>cancel</tt> is called,
   * this task should never run. If the task has already started,
   * then the <tt>mayInterruptIfRunning</tt> parameter determines
   * whether the thread executing this task should be interrupted in
   * an attempt to stop the task.
   *
   * <p>After this method returns, subsequent calls to {@link #isDone} will
   * always return <tt>true</tt>. Subsequent calls to {@link #isCancelled}
   * will always return <tt>true</tt> if this method returned <tt>true</tt>.
   *
   * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
   * task should be interrupted; otherwise, in-progress tasks are allowed
   * to complete
   * @return <tt>false</tt> if the task could not be cancelled,
   * typically because it has already completed normally;
   * <tt>true</tt> otherwise
   */
  boolean cancel(boolean mayInterruptIfRunning);
 
  /**
   * Returns <tt>true</tt> if this task was cancelled before it completed
   * normally.
   *
   * @return <tt>true</tt> if this task was cancelled before it completed
   */
  boolean isCancelled();
 
  /**
   * Returns <tt>true</tt> if this task completed.
   *
   * Completion may be due to normal termination, an exception, or
   * cancellation -- in all of these cases, this method will return
   * <tt>true</tt>.
   *
   * @return <tt>true</tt> if this task completed
   */
  boolean isDone();
 
  /**
   * Waits if necessary for the computation to complete, and then
   * retrieves its result.
   *
   * @return the computed result
   * @throws CancellationException if the computation was cancelled
   * @throws ExecutionException if the computation threw an
   * exception
   * @throws InterruptedException if the current thread was interrupted
   * while waiting
   */
  V get() throws InterruptedException, ExecutionException;
 
  /**
   * Waits if necessary for at most the given time for the computation
   * to complete, and then retrieves its result, if available.
   *
   * @param timeout the maximum time to wait
   * @param unit the time unit of the timeout argument
   * @return the computed result
   * @throws CancellationException if the computation was cancelled
   * @throws ExecutionException if the computation threw an
   * exception
   * @throws InterruptedException if the current thread was interrupted
   * while waiting
   * @throws TimeoutException if the wait timed out
   */
  V get(long timeout, TimeUnit unit)
    throws InterruptedException, ExecutionException, TimeoutException;
}

 /**
   * Submits a value-returning task for execution and returns a
   * Future representing the pending results of the task. The
   * Future's <tt>get</tt> method will return the task's result upon
   * successful completion.
   *
   * <p>
   * If you would like to immediately block waiting
   * for a task, you can use constructions of the form
   * <tt>result = exec.submit(aCallable).get();</tt>
   *
   * <p> Note: The {@link Executors} class includes a set of methods
   * that can convert some other common closure-like objects,
   * for example, {@link java.security.PrivilegedAction} to
   * {@link Callable} form so they can be submitted.
   *
   * @param task the task to submit
   * @return a Future representing pending completion of the task
   * @throws RejectedExecutionException if the task cannot be
   *     scheduled for execution
   * @throws NullPointerException if the task is null
   */
  <T> Future<T> submit(Callable<T> task);
 
  /**
   * Submits a Runnable task for execution and returns a Future
   * representing that task. The Future's <tt>get</tt> method will
   * return the given result upon successful completion.
   *
   * @param task the task to submit
   * @param result the result to return
   * @return a Future representing pending completion of the task
   * @throws RejectedExecutionException if the task cannot be
   *     scheduled for execution
   * @throws NullPointerException if the task is null
   */
  <T> Future<T> submit(Runnable task, T result);
 
  /**
   * Submits a Runnable task for execution and returns a Future
   * representing that task. The Future's <tt>get</tt> method will
   * return <tt>null</tt> upon <em>successful</em> completion.
   *
   * @param task the task to submit
   * @return a Future representing pending completion of the task
   * @throws RejectedExecutionException if the task cannot be
   *     scheduled for execution
   * @throws NullPointerException if the task is null
   */
  Future<?> submit(Runnable task);

Future<List> future = getDataFromRemoteByFuture();
    //do something....
    List data = future.get();

private Future<List> getDataFromRemoteByFuture() {
 
    return threadPool.submit(new Callable<List>() {
      @Override
      public List call() throws Exception {
        return getDataFromRemote();
      }
    });
  }

 FutureTask<List> futureTask = new FutureTask<List>(new Callable<List>() {
      @Override
      public List call() throws Exception {
        return getDataFromRemote();
      }
    });
 
    threadPool.submit(futureTask); 
    futureTask.get();

public interface Runnable { 
  public abstract void run(); 
} 

 public interface Callable<V> {  
  V  call()  throws Exception;  
 }  

  <T> Future<T> submit(Callable<T> task); 
  <T> Future<T> submit(Runnable task, T result); 
  Future<?> submit(Runnable task); 

  public interface Future<V> { 
    boolean cancel(boolean mayInterruptIfRunning); 
    boolean isCancelled(); 
    boolean isDone(); 
    V get() throws InterruptedException, ExecutionException; 
    V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; 
  } 

public class FutureTask<V> implements RunnableFuture<V> { 
FutureTask类实现了RunnableFuture接口，我们看一下RunnableFuture接口的实现：
  public interface RunnableFuture<V> extends Runnable, Future<V> { 
    void run(); 
  } 

  public FutureTask(Callable<V> callable) { 
  } 
  public FutureTask(Runnable runnable, V result) { 
  } 

package com.zejian.Executor; 
import java.util.concurrent.Callable; 
/** 
 * @author zejian 
 * @time 2016年3月15日 下午2:02:42 
 * @decrition Callable接口实例 
 */ 
public class CallableDemo implements Callable<Integer> { 
   
  private int sum; 
  @Override 
  public Integer call() throws Exception { 
    System.out.println("Callable子线程开始计算啦！"); 
    Thread.sleep(2000); 
     
    for(int i=0 ;i<5000;i++){ 
      sum=sum+i; 
    } 
    System.out.println("Callable子线程计算结束！"); 
    return sum; 
  } 
} 

  package com.zejian.Executor; 
  import java.util.concurrent.ExecutorService; 
  import java.util.concurrent.Executors; 
  import java.util.concurrent.Future; 
  /** 
   * @author zejian 
   * @time 2016年3月15日 下午2:05:43 
   * @decrition callable执行测试类 
   */ 
  public class CallableTest { 
     
    public static void main(String[] args) { 
      //创建线程池 
      ExecutorService es = Executors.newSingleThreadExecutor(); 
      //创建Callable对象任务 
      CallableDemo calTask=new CallableDemo(); 
      //提交任务并获取执行结果 
      Future<Integer> future =es.submit(calTask); 
      //关闭线程池 
      es.shutdown(); 
      try { 
        Thread.sleep(2000); 
      System.out.println("主线程在执行其他任务"); 
       
      if(future.get()!=null){ 
        //输出获取到的结果 
        System.out.println("future.get()-->"+future.get()); 
      }else{ 
        //输出获取到的结果 
        System.out.println("future.get()未获取到结果"); 
      } 
       
      } catch (Exception e) { 
        e.printStackTrace(); 
      } 
      System.out.println("主线程在执行完成"); 
    } 
  } 

  package com.zejian.Executor; 
  import java.util.concurrent.ExecutorService; 
  import java.util.concurrent.Executors; 
  import java.util.concurrent.Future; 
  import java.util.concurrent.FutureTask; 
  /** 
   * @author zejian 
   * @time 2016年3月15日 下午2:05:43 
   * @decrition callable执行测试类 
   */ 
  public class CallableTest { 
     
    public static void main(String[] args) { 
  //   //创建线程池 
  //   ExecutorService es = Executors.newSingleThreadExecutor(); 
  //   //创建Callable对象任务 
  //   CallableDemo calTask=new CallableDemo(); 
  //   //提交任务并获取执行结果 
  //   Future<Integer> future =es.submit(calTask); 
  //   //关闭线程池 
  //   es.shutdown(); 
       
      //创建线程池 
      ExecutorService es = Executors.newSingleThreadExecutor(); 
      //创建Callable对象任务 
      CallableDemo calTask=new CallableDemo(); 
      //创建FutureTask 
      FutureTask<Integer> futureTask=new FutureTask<>(calTask); 
      //执行任务 
      es.submit(futureTask); 
      //关闭线程池 
      es.shutdown(); 
      try { 
        Thread.sleep(2000); 
      System.out.println("主线程在执行其他任务"); 
       
      if(futureTask.get()!=null){ 
        //输出获取到的结果 
        System.out.println("futureTask.get()-->"+futureTask.get()); 
      }else{ 
        //输出获取到的结果 
        System.out.println("futureTask.get()未获取到结果"); 
      } 
       
      } catch (Exception e) { 
        e.printStackTrace(); 
      } 
      System.out.println("主线程在执行完成"); 
    } 
  }