描述：使用等待超时模式来构造一个简单的数据库连接池，在示例中模拟从连接池中获取、使用和释放连接的过程。客户端获取连接的过程被设计成等待超时模式

1 /*  2 连接池的定义。通过构造函数初始化连接的最大上限，通过双向队列维护连接。调用方需要先调用fetchConnection（long）  3 方法来指定在多少毫秒内超时获取连接，当连接使用完时，需要调用releaseConnection（Connection）方法来将来凝结放回  4 线程池  5  */  6 class ConnectionPool{  7     private LinkedList
     
       pool = new LinkedList
      
       ();  8     public ConnectionPool(int initialSize){  9         if (initialSize > 0){ 10             for (int i = 0; i < initialSize; i++){ 11                 pool.addLast(ConnectionDriver.creatConnection()); 12             } 13         } 14     } 15     public void releaseConnection(Connection connection){ 16         if(connection != null){ 17             synchronized (pool){ 18                 //连接释放后需要进行通知，这样其他消费者能够感知到连接池中已经归还了一个连接 19                 pool.addLast(connection);///? 20                 pool.notifyAll(); 21             } 22         } 23     } 24  25     //在mills内无法获得连接，将会返回null 26     public Connection fetchConnection(long mills) throws InterruptedException{ 27         synchronized (pool){ 28             //完全超时 29             if (mills <= 0){ 30                 while (pool.isEmpty()){ 31                     pool.wait(); 32                 } 33                 return pool.removeFirst(); 34             }else { 35                 long future = System.currentTimeMillis() + mills; 36                 long remaining = mills; 37                 while (pool.isEmpty() && remaining > 0){ 38                     pool.wait(remaining); 39                     remaining = future - System.currentTimeMillis(); 40                 } 41                 Connection result = null; 42                 if (!pool.isEmpty()){ 43                     result = pool.removeFirst(); 44                 } 45                 return result; 46             } 47         } 48     } 49 } 50 /* 51 由于java.sql.Connection是一个接口，最终实现是由数据库驱动提供方案来实现的，这里通过动态代理构造了一个Connection， 52 该Connection的代理实现仅仅实在commit方法调用时休眠100毫秒 53  */ 54 class ConnectionDriver{ 55     static class ConnectionHander implements InvocationHandler{ 56         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable{ 57             if (method.getName().equals("commit")){ 58                 TimeUnit.MILLISECONDS.sleep(100); 59             } 60             return null; 61         } 62     } 63     //创建一个Connection的代理，在commit时休眠100毫秒 64     public static final Connection creatConnection(){ 65         return (Connection) Proxy.newProxyInstance(ConnectionHander.class.getClassLoader(), 66                 new Class
       [] {Connection.class},new ConnectionHander()); 67     } 68 } 69  70 /* 71 测试，客户端模拟ConnectionRunner获取、使用、释放连接的过程 72  */ 73 class ConnectionPoolTest{ 74     static ConnectionPool pool = new ConnectionPool(10); 75     //保证所有的ConnectionRunner能同时开始 76     static CountDownLatch start = new CountDownLatch(1); 77     //main线程将会等待所有ConnectionRunner结束后才能继续执行 78     static CountDownLatch end; 79     public static void main(String[] args) throws Exception{ 80         //线程数量，可以修改线程数量进行观察 81         int threadCount = 20; 82         end = new CountDownLatch(threadCount); 83         int count = 20; 84         AtomicInteger got = new AtomicInteger(); 85         AtomicInteger notGot = new AtomicInteger(); 86         for (int i = 0; i < threadCount; i++){ 87             Thread thread = new Thread(new ConnectionRunner(count, got, notGot), "ConnectionRunnerThread"); 88             thread.start(); 89         } 90         start.countDown();//只要计数器为0，那么线程就可以结束阻塞往下执行,进而保证线程同时开始 91         end.await(); 92         System.out.println("total invoke: " + (threadCount * count)); 93         System.out.println("got connection: " + got); 94         System.out.println("not got connection: " + notGot); 95     } 96  97     static class ConnectionRunner implements Runnable{ 98         int count; 99         AtomicInteger got;100         AtomicInteger notGot;101         public ConnectionRunner(int count, AtomicInteger got, AtomicInteger notGot){102             this.count = count;103             this.got = got;104             this.notGot = notGot;105         }106         @Override107         public void run(){108             try{109                 start.await();110             }catch (Exception ex){111             }112             while (count > 0){113                 try {114                     //从线程池中获取连接，如果1000ms内无法获取到，将会返回null115                     //分别统计连接获取的数量got和未获取到的数量notGot116                     Connection connection = pool.fetchConnection(1000);117                     if (connection != null){118                         try {119                             connection.createStatement();120                             connection.commit();121                         }finally {122                             pool.releaseConnection(connection);123                             got.getAndIncrement();124                         }125                     }else {126                         notGot.getAndIncrement();127                     }128                 }catch (Exception ex){129                 }finally {130                     count--;131                 }132             }133             end.countDown();134         }135     }136 }
      
     

输出结果：

1 total invoke: 4002 got connection: 3983 not got connection: 2