1 public class MyTest {
 2     /**
 3     * 开启了20个线程,返回的hashcode,如下:没有重复的
 4     *1730967171    1122742512    156948859    1210106945    1217158489
 5     *1868341939    1595154849    1873764403    1937202425    1629470861
 6     */
 7     public static void main(String[] args) {
 8         for (int i = 0; i < 10; i++) {
 9             new Thread(new Runnable() {
10                 @Override
11                 public void run() {
12
13                     Connection con = JDBCUtil.getConnection();
14                     System.out.println(con.hashCode());
15                     // ....
16                     con.close();
17                     } catch (SQLException e) {
18                         e.printStackTrace();
19                     }
20                 }
21             }).start();
22         }
23     }
24 }
25 public class JDBCUtil {
26     /**
27     * <!-- 最大空闲时间设置为0 , 即永不过期 -->
28     * <property name="maxIdleTime">0</property>
29     * <!-- 最多有多少个连接 -->
30     * <property name="maxPoolSize">5</property>
31     * <!-- 最少几个连接 -->
32     * <property name="minPoolSize">2</property>
33     */
34     private static Connection conn;
35     private static ComboPooledDataSource ds = new ComboPooledDataSource();
36
37     public static Connection getConnection() {
38             try {
39                 conn = ds.getConnection();
40             } catch (SQLException e) {
41                 e.printStackTrace();
42             }
43         return conn;
44     }
45 }

 1 abstract class AbstractPoolBackedDataSource
 2         extends PoolBackedDataSourceBase
 3             implements PooledDataSource{
 4 //.....
 5
 6     // dataSource.getConnection()所调用的就是该方法
 7     //implementation of javax.sql.DataSource
 8     public Connection getConnection() throws SQLException{
 9
10         PooledConnection pc =
11                 getPoolManager(). // 返回 C3P0PooledConnectionPoolManager
12                 getPool(). // 返回 C3P0PooledConnectionPool
13                 checkoutPooledConnection(); // 返回PooledConnection
14         return pc.getConnection();
15     }
16
17 //.....
18 }
19
20
21
22 class C3P0PooledConnectionPool{
23     // ....
24      public PooledConnection checkoutPooledConnection() throws SQLException{
25         //System.err.println(this + " -- CHECKOUT");
26         try
27         {
28         PooledConnection pc = (PooledConnection) this.checkoutAndMarkConnectionInUse();
29         pc.addConnectionEventListener( cl );
30         return pc;
31         }
32         catch (TimeoutException e)
33         { throw SqlUtils.toSQLException("An attempt by a client to checkout a Connection has timed out.", e); }
34         catch (CannotAcquireResourceException e)
35         { throw SqlUtils.toSQLException("Connections could not be acquired from the underlying database!", "08001", e); }
36         catch (Exception e)
37         { throw SqlUtils.toSQLException(e); }
38     }
39
40     private Object checkoutAndMarkConnectionInUse() throws TimeoutException, CannotAcquireResourceException, ResourcePoolException, InterruptedException
41     {
42         Object out = null;
43     boolean success = false;
44     while (! success)
45         {
46         try
47             {
48             out = rp.checkoutResource( checkoutTimeout );
49             if (out instanceof AbstractC3P0PooledConnection)
50                 {
51                 // cast should succeed, because effectiveStatementCache implies c3p0 pooled Connections
52                 AbstractC3P0PooledConnection acpc = (AbstractC3P0PooledConnection) out;
53                 /*
54                  *以下在获取物理连接的时候,PooledcConnection中注册的事件监听器会收到消息
55                  *无论每次对connection的何种操作,PooledConnection都会收到来自驱动的消息,
56                  *其中的钩子(hook)对象就会完成对Connection的回收
57                  */
58                 Connection physicalConnection = acpc.getPhysicalConnection();
59                 success = tryMarkPhysicalConnectionInUse(physicalConnection);
60                 }
61             else
62                 success = true; //we don't pool statements from non-c3p0 PooledConnections
63             }
64         finally
65             {
66             try { if (!success && out != null) rp.checkinResource( out );}
67             catch (Exception e) { logger.log(MLevel.WARNING, "Failed to check in a Connection that was unusable due to pending Statement closes.", e); }
68             }
69             }
70         return out;
71     }
72     //....
73
74 }