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

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1. ComboPooledDataSource cpds = new ComboPooledDataSource(); cpds.setDriverClass( "org.postgresql.Driver" );
2. cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" ); cpds.setUser("swaldman");
3. cpds.setPassword("test-password");
4. // 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
5. cpds.setMinPoolSize(5);
6. cpds.setAcquireIncrement(5);
7. cpds.setMaxPoolSize(20);

也可以使用命名Configuration

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1. 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。

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1. DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", "swaldman", "test-password");
2. DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled );
3. // 此时DataSource已经可以使用，但应该显示的设置driver Class
4. 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

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

如果使用命名的Configuration，可以如下

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

销毁DataSource有两种方式

DataSource.destroy()方式

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1. DataSource ds_pooled = null;
2. try {
3. DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", "swaldman", "test-password");
4. ds_pooled = DataSources.pooledDataSource( ds_unpooled );
5. // 下面正常使用DataSource...
6. }
7. finally {
8. DataSources.destroy( ds_pooled );
9. }

另一种是PooledDataSource 接口提供的close() 方法

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1. static void cleanup(DataSource ds) throws SQLException {
2. // 确定是否为c3p0的PooledDataSource
3. if ( ds instanceof PooledDataSource) {
4. PooledDataSource pds = (PooledDataSource) ds;
5. pds.close();
6. } else
7. System.err.println("Not a c3p0 PooledDataSource!");
8. }