C3p0创建方式

c3p0有3种创建方式（1）直接实例化并配置comboPooledDataSource bean。（2）使用DataSources工厂类。（3）实现PoolBackedDataSource类（abstract类）。即实现自己的DataSource。

一、实例化并配置ComboPooledDataSource

ComboPooledDataSource cpds = new ComboPooledDataSource();
cpds.setDriverClass( "org.postgresql.Driver" ); //loads the jdbc driver            
cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" );
cpds.setUser("swaldman");                                  
cpds.setPassword("test-password");                                  
    
// the settings below are optional -- c3p0 can work with defaults
cpds.setMinPoolSize(5);                                     
cpds.setAcquireIncrement(5);
cpds.setMaxPoolSize(20);
    
// The DataSource cpds is now a fully configured and usable pooled DataSource

If you obtain a DataSource by instantiating a ComboPooledDataSource
, configure it by simply calling appropriate setter methods offered by that class before attempting a call to getConnection()
.

常用的最直接的方式是实例化ComboPooledDataSource。这是一个JavaBean风格的类，提供一个public，无参的构造器。配置参数至少要求配置jdbcUrl。

c3p0支持以name命名的数据源。ComboPooledDataSource提供一个String的构造器，传入name即可。

ComboPooledDataSource cpds = new ComboPooledDataSource("intergalactoApp");

二、使用DataSources facotry工厂类

另一种方法是通过DataSources工厂类创建unpooled DataSource数据源,并且可通过unpooled DataSource创建pooled DataSource。

DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb", 
                                                        "swaldman", 
                                                        "test-password");
DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled );

自定义配置项
指定一个Map存放配置项，使用pooledDataSource重载方法。

Map overrides = new HashMap();
overrides.put("maxStatements", "200");         //Stringified property values work
overrides.put("maxPoolSize", new Integer(50)); //"boxed primitives" also work

// create the PooledDataSource using the default configuration and our overrides
ds_pooled = DataSources.pooledDataSource( ds_unpooled, overrides ); 

为数据源指定名字
pooledDataSource重在方法提供命名name

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