线程池的应用及Callable接口的使用

Java代码 复制代码 收藏代码
  1. public interface Executor {   
  2.   
  3.     /**  
  4.      * Executes the given command at some time in the future.  The command  
  5.      * may execute in a new thread, in a pooled thread, or in the calling  
  6.      * thread, at the discretion of the <tt>Executor</tt> implementation.  
  7.      *  
  8.      * @param command the runnable task  
  9.      * @throws RejectedExecutionException if this task cannot be  
  10.      * accepted for execution.  
  11.      * @throws NullPointerException if command is null  
  12.      */  
  13.     void execute(Runnable command);   
  14. }  
public interface Executor {

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the <tt>Executor</tt> implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution.
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}
Java代码 复制代码 收藏代码
  1. //接口ExecutorService继承自Executor，它的目的是为我们管理Thread对象，从而简化并发编程   
  2. public interface ExecutorService extends Executor {   
  3.   
  4.     <T> Future<T> submit(Callable<T> task);   
  5.       
  6.     <T> Future<T> submit(Runnable task, T result);   
  7.   
  8.     Future<?> submit(Runnable task);   
  9.        
  10.     ...      
  11. }  
//接口ExecutorService继承自Executor，它的目的是为我们管理Thread对象，从而简化并发编程
public interface ExecutorService extends Executor {

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

    Future<?> submit(Runnable task);
	
    ...   
}
Java代码 复制代码 收藏代码
  1. public interface Callable<V> {   
  2.     /**  
  3.      * Computes a result, or throws an exception if unable to do so.  
  4.      *  
  5.      * @return computed result  
  6.      * @throws Exception if unable to compute a result  
  7.      */  
  8.     V call() throws Exception;   
  9. }   
  10.   
  11.   
  12. public interface Runnable {   
  13.       
  14.     public abstract void run();   
  15. }  
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 Runnable {
   
    public abstract void run();
}
Java代码 复制代码 收藏代码
  1. public interface Future<V> {   
  2.        
  3.     boolean cancel(boolean mayInterruptIfRunning);       
  4.   
  5.     /**  
  6.      * Waits if necessary for the computation to complete, and then  
  7.      * retrieves its result.  
  8.      *  
  9.      * @return the computed result    
  10.      */  
  11.     V get() throws InterruptedException, ExecutionException;   
  12.   
  13.       
  14.     V get(long timeout, TimeUnit unit)   
  15.         throws InterruptedException, ExecutionException, TimeoutException;   
  16. }  
public interface Future<V> {
    
    boolean cancel(boolean mayInterruptIfRunning);    

    /**
     * Waits if necessary for the computation to complete, and then
     * retrieves its result.
     *
     * @return the computed result  
     */
    V get() throws InterruptedException, ExecutionException;

   
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}

Callable接口和Runnable接口相似，区别就是Callable需要实现call方法，而Runnable需要实现run方法；并且，call方法还可以返回任何对象，无论是什么对象，JVM都会当作Object来处理。但是如果使用了泛型，我们就不用每次都对Object进行转换了。

 

Runnable和Callable都是接口

不同之处：
1.Callable可以返回一个类型V，而Runnable不可以
2.Callable能够抛出checked exception,而Runnable不可以。
3.Runnable是自从java1.1就有了，而Callable是1.5之后才加上去的
4.Callable和Runnable都可以应用于executors。而Thread类只支持Runnable.
上面只是简单的不同，其实这两个接口在用起来差别还是很大的。Callable与executors联合在一起，在任务完成时可立刻获得一个更新了的Future。而Runable却要自己处理

 

  Future接口，一般都是取回Callable执行的状态用的。其中的主要方法：

  • cancel，取消Callable的执行，当Callable还没有完成时
  • get，获得Callable的返回值
  • isCanceled，判断是否取消了
  • isDone，判断是否完成

 

用Executor来构建线程池，应该要做的事：

1).调用Executors类中的静态方法newCachedThreadPool(必要时创建新线程，空闲线程会被保留60秒)或newFixedThreadPool(包含固定数量的线程池)等，返回的是一个实现了ExecutorService接口的ThreadPoolExecutor类或者是一个实现了ScheduledExecutorServiece接口的类对象。

2).调用submit提交Runnable或Callable对象。

3).如果想要取消一个任务，或如果提交Callable对象，那就要保存好返回的Future对象。

4).当不再提交任何任务时，调用shutdown方法。

 

举2个例子如下：

Java代码   收藏代码
  1. package thread.test04;  
  2. import java.util.concurrent.*;  
  3. public class ThreadTestA {  
  4.     public static void main(String[] args) {  
  5.         ExecutorService e=Executors.newFixedThreadPool(10);  
  6.         e.execute(new MyRunnableA());  
  7.         e.execute(new MyRunnableB());  
  8.        e.shutdown();  
  9.    }  
  10.   
  11. }  
  12.   
  13. class MyRunnableA implements Runnable{  
  14.       
  15.     public void run(){  
  16.         System.out.println("Runnable:run()....");  
  17.         int i=0;  
  18.         while(i<20){  
  19.             i++;  
  20.             for(int j=0;j<1000000;j++);  
  21.             System.out.println("i="+i);  
  22.         }  
  23.     }  
  24. }  
  25.   
  26. class MyRunnableB implements Runnable{  
  27.     public void run(){  
  28.         char c='A'-1;  
  29.         while(c<'Z'){  
  30.             c++;  
  31.             for(int j=0;j<1000000;j++);  
  32.             System.out.println("c="+c);  
  33.         }  
  34.     }  
  35. }  

 

Java代码   收藏代码
  1. package thread.test04;  
  2.   
  3. import java.util.concurrent.Callable;  
  4. import java.util.concurrent.ExecutionException;  
  5. import java.util.concurrent.ExecutorService;  
  6. import java.util.concurrent.Executors;  
  7. import java.util.concurrent.Future;  
  8.   
  9. public class ThreadTestB {  
  10.     public static void main(String[] args) {  
  11.         ExecutorService e=Executors.newFixedThreadPool(10);  
  12.         Future f1=e.submit(new MyCallableA());  
  13.         Future f2=e.submit(new MyCallableA());  
  14.         Future f3=e.submit(new MyCallableA());        
  15.         System.out.println("--Future.get()....");  
  16.         try {  
  17.             System.out.println(f1.get());  
  18.             System.out.println(f2.get());  
  19.             System.out.println(f3.get());            
  20.         } catch (InterruptedException e1) {  
  21.             e1.printStackTrace();  
  22.         } catch (ExecutionException e1) {  
  23.             e1.printStackTrace();  
  24.         }  
  25.           
  26.         e.shutdown();  
  27.           
  28.     }  
  29.   
  30. }  
  31.   
  32. class MyCallableA implements Callable<String>{  
  33.     public String call() throws Exception {  
  34.         System.out.println("开始执行Callable");  
  35.         String[] ss={"zhangsan","lisi"};  
  36.         long[] num=new long[2];  
  37.         for(int i=0;i<1000000;i++){  
  38.             num[(int)(Math.random()*2)]++;  
  39.         }  
  40.           
  41.         if(num[0]>num[1]){  
  42.             return ss[0];  
  43.         }else if(num[0]<num[1]){  
  44.             throw new Exception("弃权!");  
  45.         }else{  
  46.             return ss[1];  
  47.         }  
  48.     }  
  49.       
  50. }  

 来源：http://junlas.iteye.com/blog/846457

Java代码 复制代码 收藏代码
  1. /**  
  2.  * Factory and utility methods for {@link Executor}, {@link  
  3.  * ExecutorService}, {@link ScheduledExecutorService}, {@link  
  4.  * ThreadFactory}, and {@link Callable} classes defined in this  
  5.  * package. This class supports the following kinds of methods:  
  6.  *  
  7.  * <ul>  
  8.  *   <li> Methods that create and return an {@link ExecutorService}  
  9.  *        set up with commonly useful configuration settings.  
  10.  *   <li> Methods that create and return a {@link ScheduledExecutorService}  
  11.  *        set up with commonly useful configuration settings.  
  12.  *   <li> Methods that create and return a "wrapped" ExecutorService, that  
  13.  *        disables reconfiguration by making implementation-specific methods  
  14.  *        inaccessible.  
  15.  *   <li> Methods that create and return a {@link ThreadFactory}  
  16.  *        that sets newly created threads to a known state.  
  17.  *   <li> Methods that create and return a {@link Callable}  
  18.  *        out of other closure-like forms, so they can be used  
  19.  *        in execution methods requiring <tt>Callable</tt>.  
  20.  * </ul>  
  21.  *  
  22.  * @since 1.5  
  23.  * @author Doug Lea  
  24.  */  
  25. public class Executors {   
  26.   
  27.     /**  
  28.      * Creates a thread pool that reuses a fixed number of threads  
  29.      * operating off a shared unbounded queue.  At any point, at most  
  30.      * <tt>nThreads</tt> threads will be active processing tasks.  
  31.      * If additional tasks are submitted when all threads are active,  
  32.      * they will wait in the queue until a thread is available.  
  33.      * If any thread terminates due to a failure during execution  
  34.      * prior to shutdown, a new one will take its place if needed to  
  35.      * execute subsequent tasks.  The threads in the pool will exist  
  36.      * until it is explicitly {@link ExecutorService#shutdown shutdown}.  
  37.      *  
  38.      * @param nThreads the number of threads in the pool  
  39.      * @return the newly created thread pool  
  40.      * @throws IllegalArgumentException if <tt>nThreads &lt;= 0</tt>  
  41.      */  
  42.     public static ExecutorService newFixedThreadPool(int nThreads) {   
  43.         return new ThreadPoolExecutor(nThreads, nThreads,   
  44.                                       0L, TimeUnit.MILLISECONDS,   
  45.                                       new LinkedBlockingQueue<Runnable>());   
  46.     }   
  47.   
  48.     /**  
  49.      * Creates a thread pool that reuses a fixed number of threads  
  50.      * operating off a shared unbounded queue, using the provided  
  51.      * ThreadFactory to create new threads when needed.  At any point,  
  52.      * at most <tt>nThreads</tt> threads will be active processing  
  53.      * tasks.  If additional tasks are submitted when all threads are  
  54.      * active, they will wait in the queue until a thread is  
  55.      * available.  If any thread terminates due to a failure during  
  56.      * execution prior to shutdown, a new one will take its place if  
  57.      * needed to execute subsequent tasks.  The threads in the pool will  
  58.      * exist until it is explicitly {@link ExecutorService#shutdown  
  59.      * shutdown}.  
  60.      *  
  61.      * @param nThreads the number of threads in the pool  
  62.      * @param threadFactory the factory to use when creating new threads  
  63.      * @return the newly created thread pool  
  64.      * @throws NullPointerException if threadFactory is null  
  65.      * @throws IllegalArgumentException if <tt>nThreads &lt;= 0</tt>  
  66.      */  
  67.     public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {   
  68.         return new ThreadPoolExecutor(nThreads, nThreads,   
  69.                                       0L, TimeUnit.MILLISECONDS,   
  70.                                       new LinkedBlockingQueue<Runnable>(),   
  71.                                       threadFactory);   
  72.     }   
  73.   
  74.     /**  
  75.      * Creates an Executor that uses a single worker thread operating  
  76.      * off an unbounded queue. (Note however that if this single  
  77.      * thread terminates due to a failure during execution prior to  
  78.      * shutdown, a new one will take its place if needed to execute  
  79.      * subsequent tasks.)  Tasks are guaranteed to execute  
  80.      * sequentially, and no more than one task will be active at any  
  81.      * given time. Unlike the otherwise equivalent  
  82.      * <tt>newFixedThreadPool(1)</tt> the returned executor is  
  83.      * guaranteed not to be reconfigurable to use additional threads.  
  84.      *  
  85.      * @return the newly created single-threaded Executor  
  86.      */  
  87.     public static ExecutorService newSingleThreadExecutor() {   
  88.         return new FinalizableDelegatedExecutorService   
  89.             (new ThreadPoolExecutor(1, 1,   
  90.                                     0L, TimeUnit.MILLISECONDS,   
  91.                                     new LinkedBlockingQueue<Runnable>()));   
  92.     }   
  93.   
  94.     /**  
  95.      * Creates an Executor that uses a single worker thread operating  
  96.      * off an unbounded queue, and uses the provided ThreadFactory to  
  97.      * create a new thread when needed. Unlike the otherwise  
  98.      * equivalent <tt>newFixedThreadPool(1, threadFactory)</tt> the  
  99.      * returned executor is guaranteed not to be reconfigurable to use  
  100.      * additional threads.  
  101.      *  
  102.      * @param threadFactory the factory to use when creating new  
  103.      * threads  
  104.      *  
  105.      * @return the newly created single-threaded Executor  
  106.      * @throws NullPointerException if threadFactory is null  
  107.      */  
  108.     public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {   
  109.         return new FinalizableDelegatedExecutorService   
  110.             (new ThreadPoolExecutor(1, 1,   
  111.                                     0L, TimeUnit.MILLISECONDS,   
  112.                                     new LinkedBlockingQueue<Runnable>(),   
  113.                                     threadFactory));   
  114.     }   
  115.   
  116.     /**  
  117.      * Creates a thread pool that creates new threads as needed, but  
  118.      * will reuse previously constructed threads when they are  
  119.      * available.  These pools will typically improve the performance  
  120.      * of programs that execute many short-lived asynchronous tasks.  
  121.      * Calls to <tt>execute</tt> will reuse previously constructed  
  122.      * threads if available. If no existing thread is available, a new  
  123.      * thread will be created and added to the pool. Threads that have  
  124.      * not been used for sixty seconds are terminated and removed from  
  125.      * the cache. Thus, a pool that remains idle for long enough will  
  126.      * not consume any resources. Note that pools with similar  
  127.      * properties but different details (for example, timeout parameters)  
  128.      * may be created using {@link ThreadPoolExecutor} constructors.  
  129.      *  
  130.      * @return the newly created thread pool  
  131.      */  
  132.     public static ExecutorService newCachedThreadPool() {   
  133.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,   
  134.                                       60L, TimeUnit.SECONDS,   
  135.                                       new SynchronousQueue<Runnable>());   
  136.     }   
  137.   
  138.     /**  
  139.      * Creates a thread pool that creates new threads as needed, but  
  140.      * will reuse previously constructed threads when they are  
  141.      * available, and uses the provided  
  142.      * ThreadFactory to create new threads when needed.  
  143.      * @param threadFactory the factory to use when creating new threads  
  144.      * @return the newly created thread pool  
  145.      * @throws NullPointerException if threadFactory is null  
  146.      */  
  147.     public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {   
  148.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,   
  149.                                       60L, TimeUnit.SECONDS,   
  150.                                       new SynchronousQueue<Runnable>(),   
  151.                                       threadFactory);   
  152.     }   
  153.   
  154.     /**  
  155.      * Creates a single-threaded executor that can schedule commands  
  156.      * to run after a given delay, or to execute periodically.  
  157.      * (Note however that if this single  
  158.      * thread terminates due to a failure during execution prior to  
  159.      * shutdown, a new one will take its place if needed to execute  
  160.      * subsequent tasks.)  Tasks are guaranteed to execute  
  161.      * sequentially, and no more than one task will be active at any  
  162.      * given time. Unlike the otherwise equivalent  
  163.      * <tt>newScheduledThreadPool(1)</tt> the returned executor is  
  164.      * guaranteed not to be reconfigurable to use additional threads.  
  165.      * @return the newly created scheduled executor  
  166.      */  
  167.     public static ScheduledExecutorService newSingleThreadScheduledExecutor() {   
  168.         return new DelegatedScheduledExecutorService   
  169.             (new ScheduledThreadPoolExecutor(1));   
  170.     }   
  171.   
  172.     /**  
  173.      * Creates a single-threaded executor that can schedule commands  
  174.      * to run after a given delay, or to execute periodically.  (Note  
  175.      * however that if this single thread terminates due to a failure  
  176.      * during execution prior to shutdown, a new one will take its  
  177.      * place if needed to execute subsequent tasks.)  Tasks are  
  178.      * guaranteed to execute sequentially, and no more than one task  
  179.      * will be active at any given time. Unlike the otherwise  
  180.      * equivalent <tt>newScheduledThreadPool(1, threadFactory)</tt>  
  181.      * the returned executor is guaranteed not to be reconfigurable to  
  182.      * use additional threads.  
  183.      * @param threadFactory the factory to use when creating new  
  184.      * threads  
  185.      * @return a newly created scheduled executor  
  186.      * @throws NullPointerException if threadFactory is null  
  187.      */  
  188.     public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {   
  189.         return new DelegatedScheduledExecutorService   
  190.             (new ScheduledThreadPoolExecutor(1, threadFactory));   
  191.     }   
  192.   
  193.     /**  
  194.      * Creates a thread pool that can schedule commands to run after a  
  195.      * given delay, or to execute periodically.  
  196.      * @param corePoolSize the number of threads to keep in the pool,  
  197.      * even if they are idle.  
  198.      * @return a newly created scheduled thread pool  
  199.      * @throws IllegalArgumentException if <tt>corePoolSize &lt; 0</tt>  
  200.      */  
  201.     public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {   
  202.         return new ScheduledThreadPoolExecutor(corePoolSize);   
  203.     }   
  204.   
  205.     /**  
  206.      * Creates a thread pool that can schedule commands to run after a  
  207.      * given delay, or to execute periodically.  
  208.      * @param corePoolSize the number of threads to keep in the pool,  
  209.      * even if they are idle.  
  210.      * @param threadFactory the factory to use when the executor  
  211.      * creates a new thread.  
  212.      * @return a newly created scheduled thread pool  
  213.      * @throws IllegalArgumentException if <tt>corePoolSize &lt; 0</tt>  
  214.      * @throws NullPointerException if threadFactory is null  
  215.      */  
  216.     public static ScheduledExecutorService newScheduledThreadPool(   
  217.             int corePoolSize, ThreadFactory threadFactory) {   
  218.         return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);   
  219.     }   
  220.     ........   
  221.   
  222.     /** Cannot instantiate. */  
  223.     private Executors() {}   
  224. }  
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原文地址：https://www.cnblogs.com/jianwei-dai/p/5741427.html