一、导入jar包

下载：Maven
c3p0-0.9.1.2.jar

二、配置文件

c3p0详细配置（c3p0-config.xml）

c3p0-config.xml名称必须一模一样
<?xml version=“1.0” encoding=“UTF-8”?>必须在文件的第一行
中文编码，&符号要写成&amp;

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
   <default-config>
     <property name="jdbcUrl">jdbc:mysql://localhost:3308/shopping?useUnicode=true&amp;characterEncoding=UTF-8</property>
     <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
     <property name="user">root</property>
     <property name="password">123456</property>
<!--       初始化大小-->
     <property name="initialPoolSize">3</property>
<!--  最多有多少个连接-->
     <property name="maxPoolSize">6</property>
<!--       最少几个连接-->
       <property name="mPoolSize">2</property>
<!--   最大空闲数-->
     <property name="maxIdleTime">1000</property>
<!--    每次最多可以执行多少个批处理语句-->
       <property name="maxStatements">50</property>
   </default-config>
  <named-config name="demo">
    <property name="user">root</property>
    <property name="password">123456</property>
    <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
    <property name="jdbcUrl">jdbc:mysql://localhost:3308/shopping?useUnicode=true&amp;characterEncoding=UTF-8</property>
    <property name="initialPoolSize">10</property>
    <property name="maxIdleTime">30</property>
    <property name="maxPoolSize">100</property>
    <property name="minPoolSize">10</property>
  </named-config>

</c3p0-config>

三、 写C3p0Utils工具类（具有初始化连接池，获得连接的方法）

// 新建数据库连接池，注意这里的参数必须同c3p0-config.xml中的named-config标签中的name的值相同
// 如果不写，则默认调用default-config

package com.itqf.utils;

import com.mchange.v2.c3p0.ComboPooledDataSource;
import java.sql.Connection;
import java.sql.SQLException;
public class C3p0Utils {
    private static ComboPooledDataSource dataSource = null;

    static {
        dataSource = new ComboPooledDataSource();
    }

    public static ComboPooledDataSource getDataSource() {
        return dataSource;
    }

    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }
}

四、C3p0Utils在Dao层使用

package com.itqf.dao.impl;

import com.itqf.dao.UserDao;
import com.itqf.entity.User;
import com.itqf.utils.C3p0Utils;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import java.sql.Connection;
import java.sql.SQLException;

/*
 * 用户模块数据库访问的实现类*/
public class UserDaoImpl implements UserDao {
    private QueryRunner queryRunner = new QueryRunner(C3p0Utils.getDataSource());
    @Override
    public User selectUserByUname(String username) {
        User user = null;
        String sql = "select u_id as uid,u_name as uname,u_password as upassword" +
                "u_email as uemail,u_sex as usex,u_status as status ,u_code as ucode" +
                "u_role as urole from user where u_name = ?";
        try {
            user = queryRunner.query(sql, new BeanHandler<User>(User.class), username);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return user;
    }
}