C3P0连接池使用小结

C3P0在最近的demo中也用了（我用的是0.9.2.1版本），因为单例很难应付大量并发。

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】

用法详见文档：http://www.mchange.com/projects/c3p0/

基本的用法在http://www.mchange.com/projects/c3p0/#quickstart，以及http://www.mchange.com/projects/c3p0/#using_c3p0中。

在项目中更为方便的做法是将配置写在配置文件中。

C0P0的配置文件名为c3p0-config.xml，详见http://www.mchange.com/projects/c3p0/#configuration_files

一个示例的配置文件如下：

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<?xml version="1.0" encoding="UTF-8"?><c3p0-config><default-config><property name="automaticTestTable">t_c3p0_test</property><property name="checkoutTimeout">10000</property><property name="idleConnectionTestPeriod">10</property><property name="initialPoolSize">5</property><property name="maxIdleTime">600</property><property name="maxPoolSize">20</property><property name="minPoolSize">2</property><property name="maxStatements">60</property><property name="maxStatementsPerConnection">3</property><user-overrides user="test-user"><property name="maxPoolSize">10</property><property name="minPoolSize">1</property><property name="maxStatements">0</property></user-overrides></default-config><named-config name="metkb"><property name="acquireIncrement">20</property><property name="initialPoolSize">10</property><property name="minPoolSize">10</property><property name="maxPoolSize">100</property><property name="maxStatements">0</property><property name="maxStatementsPerConnection">10</property><!-- he's important, but there's only one of him --><user-overrides user="master-of-the-universe"><property name="acquireIncrement">1</property><property name="initialPoolSize">1</property><property name="minPoolSize">1</property><property name="maxPoolSize">5</property><property name="maxStatementsPerConnection">50</property></user-overrides></named-config></c3p0-config>

放在eclipse Web工程的src目录下即可（eclipse会将该目录下的配置文件复制到tomcat的webapps/XXX/WEB-INF/classes下）

一个C3P0的单例的示例代码如下（连接池的单例并不妨碍并发，因为从连接池中取连接并不费时，而且取出的连接是线程安全的）：

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】

package cn.edu.ruc.metkb.util;import java.beans.PropertyVetoException;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import com.mchange.v2.c3p0.ComboPooledDataSource;public class PooledDBA implements DBA{private ComboPooledDataSource cpds = null;private static Log dblog = null;private static String DBClassName = null;private static String DBName = null;private static String DBUrl = null;private static String DBUser = null;private static String DBPassword = null;protected PooledDBA(){cpds = new ComboPooledDataSource("metkb");try{cpds.setDriverClass( DBClassName );}catch (PropertyVetoException e){dblog.exception(e);}           cpds.setJdbcUrl( DBUrl + DBName);cpds.setUser(DBUser);                                  cpds.setPassword(DBPassword);}static{try{DBClassName = ConfigFactory.getInstance().get("db.classname");DBName = ConfigFactory.getInstance().get("db.name");DBUrl = ConfigFactory.getInstance().get("db.url");DBUser = ConfigFactory.getInstance().get("db.user");DBPassword = ConfigFactory.getInstance().get("db.password");dblog = LogFactory.getInstance().getLog("db");}catch (Exception e){e.printStackTrace();}}@Overridepublic synchronized Connection getConnection() throws SQLException, ClassNotFoundException, InterruptedException{return cpds.getConnection();}@Overridepublic synchronized void close(Connection conn){try{if (conn != null){conn.close();conn = null;}}catch (SQLException e){dblog.exception(e);}}@Overridepublic synchronized void close(Statement stat){try{if (stat != null){stat.close();stat = null;}}catch (SQLException e){dblog.exception(e);}}@Overridepublic synchronized void close(ResultSet rest){try{if (rest != null){rest.close();rest = null;}}catch (SQLException e){dblog.exception(e);}}}

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】