[Java知识库]javaWeb:jdbc连接池学习2:C3P0

1.C3P0是什么?

C3P0是一个开源的JDBC连接池，它实现了数据源和JNDI绑定，支持JDBC3规范和JDBC2的标准扩展。使用它的开源项目有Hibernate、Spring等。

2.使用C3P0：

ComboPooledDataSource dataSource = new ComboPooledDataSource();//创建c3p0对象

import com.mchange.v2.c3p0.ComboPooledDataSource;

import java.beans.PropertyVetoException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Dbutilsr {



    public static void main(String[] args) {


        PreparedStatement pstmt;
        ResultSet rs = null;


        try {
            ComboPooledDataSource dataSource = new ComboPooledDataSource();

            dataSource.setDriverClass("com.mysql.jdbc.Driver");
            dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/new_schema");
            dataSource.setUser("root");
            dataSource.setPassword("your-password");

            Connection conn = dataSource.getConnection(); //连接数据库
            String sql = "select * from user";

            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {

                System.out.println(rs.getString("password"));


            }


        } catch (PropertyVetoException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }}

效果：

2.c3p0配置文件：

打开：c3po的index.html

有：下面代码：
c3p0 will look for an XML configuration file in its classloader’s resource path under the name “/c3p0-config.xml”.//
c3po将会从xml配置文件读取数据：默认文件名：
c3p0-config.xml
所以要创建c3p0-config.xml这个文件，并粘贴下面代码

c3p0-config.xml代码xml里面

 <property name="driverClass">com.mysql.jdbc.Driver</property>

name=“driverClass”:等会有一个c3po对象类：会读取这里driverClass 是 这个com.mysql.jdbc.Driver
c3po对象类:就可以不用写这个（数据库驱动了）
dataSource.setDriverClass(“com.mysql.jdbc.Driver”);
其他类似

<default-config> //默认c3p0对象读取这个信息

 <named-config name="oracel">  //name="oracel",切换数据

（c3p0-config.xml代码）

<?xml version="1.0" encoding="UTF-8" ?>
<c3p0-config>
    <default-config>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/new_schema</property>
        <property name="user">root</property>
        <property name="password">your-password</property>



    </default-config>

    <!-- This app is massive! -->
    <named-config name="oracel">  //name="oracel",切换数据
    <property name="DriverClass">com.mysql.jdbc.Driver</property>
    <property name="JdbcUrl">jdbc:mysql://localhost:3306/new_schema</property>
    <property name="User">root</property>
    <property name="Password">your-password</property>
    </named-config>
</c3p0-config>

实现类代码：

import com.mchange.v2.c3p0.ComboPooledDataSource;

import java.beans.PropertyVetoException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Dbutilsr {



    public static void main(String[] args) {


        PreparedStatement pstmt;
        ResultSet rs = null;


        try {
            ComboPooledDataSource dataSource = new ComboPooledDataSource();

            // dataSource.setDriverClass("com.mysql.jdbc.Driver");
            // dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/new_schema");
            // dataSource.setUser("root");
            // dataSource.setPassword("your-password");

            Connection conn = dataSource.getConnection(); //连接数据库
            String sql = "select * from user";

            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {

                System.out.println(rs.getString("password"));


            }


        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }}

效果图：

注意：
ComboPooledDataSource dataSource = new ComboPooledDataSource(“oracel”); //参数oracel
c3p0对象：读取：xml里面的这个
named-config name="oracel"

 <!-- This app is massive! -->
    <named-config name="oracel">  //name="oracel",切换数据
    <property name="DriverClass">com.mysql.jdbc.Driver</property>
    <property name="JdbcUrl">jdbc:mysql://localhost:3306/new_schema</property>
    <property name="User">root</property>
    <property name="Password">your-password</property>
    </named-config>

也运行成功了

学习中遇到的问题：

c3p0 版本不合适，出现错误
和jdbc驱动：mysql-connection-java-8.0.27

配置这个：c3p0-0.9.5.5jar 错误
配置这个：c3p0-0.9.1.2jar 成功
c3p0-0.9.1.2jar ;下载链接：

https://mvnrepository.com/artifact/c3p0/c3p0/0.9.1.2

这个：

可以点击：jar