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 hereDataSource 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. }