Java中使用C3P0连接池

先看官网给的范例：

import java.sql.*;
import javax.naming.*;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.DataSources;


/**
 *  This example shows how to acquire a c3p0 DataSource and
 *  bind it to a JNDI name service.
 */
public final class JndiBindDataSource
{
    // be sure to load your database driver class, either via 
    // Class.forName() [as shown below] or externally (e.g. by
    // using -Djdbc.drivers when starting your JVM).
    static
    {
	try 
	    { Class.forName( "com.mysql.jdbc.Driver" ); }
	catch (Exception e) 
	    { e.printStackTrace(); }
    }

    public static void main(String[] argv)
    {
	try
	    {
		// let a command line arg specify the name we will
		// bind our DataSource to.
		String jndiName = argv[0];

  		// acquire the DataSource using default pool params... 
  		// this is the only c3p0 specific code here
		DataSource unpooled = DataSources.unpooledDataSource("jdbc:mysql://127.0.0.1:3306/gpsdata",
								     "root",
								     "root");
		DataSource pooled = DataSources.pooledDataSource( unpooled );

		// Create an InitialContext, and bind the DataSource to it in 
		// the usual way.
		//
		// We are using the no-arg version of InitialContext's constructor,
		// therefore, the jndi environment must be first set via a jndi.properties
		// file, System properties, or by some other means.
		InitialContext ctx = new InitialContext();
		ctx.rebind( jndiName, pooled );
		System.out.println("DataSource bound to nameservice under the name \"" +
				   jndiName + '\"');
	    }
	catch (Exception e)
	    { e.printStackTrace(); }
    }

    static void attemptClose(ResultSet o)
    {
	try
	    { if (o != null) o.close();}
	catch (Exception e)
	    { e.printStackTrace();}
    }

    static void attemptClose(Statement o)
    {
	try
	    { if (o != null) o.close();}
	catch (Exception e)
	    { e.printStackTrace();}
    }

    static void attemptClose(Connection o)
    {
	try
	    { if (o != null) o.close();}
	catch (Exception e)
	    { e.printStackTrace();}
    }

    private JndiBindDataSource()
    {}
}

 1.建立 com.mchange.v2.c3p0.ComboPooledDataSource

这是一个JavaBean，在使用前应设置它的jdbcURL、user、password和driverClass。其他参数参考configuration properties

 ComboPooledDataSource cpds = new ComboPooledDataSource(); cpds.setDriverClass( "org.postgresql.Driver" );
 cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" ); cpds.setUser("swaldman");
 cpds.setPassword("test-password");
 // 下面的设置是可选的，c3p0可以在默认条件下工作，也可以设置其他条件
 cpds.setMinPoolSize(5);
 cpds.setAcquireIncrement(5);
 cpds.setMaxPoolSize(20);

也可以使用命名Configuration

 ComboPooledDataSource cpds = new ComboPooledDataSource("intergalactoApp");

2.使用工厂类com.mchange.v2.c3p0.DataSources

com.mchange.v2.c3p0.DataSources 可以按照传统的JDBC驱动建立一个无连接池的DataSource，然后转化为连接池的DataSource。

 DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", "swaldman", "test-password");
 DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled );
 // 此时DataSource已经可以使用，但应该显示的设置driver Class
 Class.forName("org.postgresql.Driver");

如果想设置其中的参数，可以将参数放入一个Map中

 DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", "swaldman", "test-password");
 Map overrides = new HashMap();
 overrides.put("maxStatements", "200"); overrides.put("maxPoolSize", new Integer(50));
 //建立一个包括默认值和设置值的PooledDataSource
 ds_pooled = DataSources.pooledDataSource( ds_unpooled, overrides );

如果使用命名的Configuration，可以如下

 ds_pooled = DataSources.pooledDataSource( ds_unpooled, "intergalactoAppConfig", overrides );

 

销毁DataSource有两种方式

DataSource.destroy()方式

 DataSource ds_pooled = null;
 try {
   DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", "swaldman", "test-password");
 ds_pooled = DataSources.pooledDataSource( ds_unpooled );
 // 下面正常使用DataSource...
 }
 finally {
   DataSources.destroy( ds_pooled );
 }

另一种是PooledDataSource 接口提供的close() 方法

 static void cleanup(DataSource ds) throws SQLException {
 // 确定是否为c3p0的PooledDataSource
 if ( ds instanceof PooledDataSource) {
   PooledDataSource pds = (PooledDataSource) ds;
   pds.close();
 } else
   System.err.println("Not a c3p0 PooledDataSource!");
 }