数据库连接池概述

在JDBC编程中，每次创建和断开Connection对象都会消耗一定的时间和IO资源。 这是因为在Java程序与数据库之间建立连接时，数据库端要验证用户名和密码并为该连接分配资源，而程序则要把代表连接Connection对象等加载到内存中，所以建立数据库连接的开销很大。尤其是在大量的并发访问时，频繁地创建、断开数据库 连接势必会影响数据库的访问效率，甚至导致数据库崩溃。

为了解决该类问题的发生诞生了数据库连接池技术。数据库连接池负责分配、管理和释放数据库连接，它允许应用程序重复使用现有的数据库连接，而不是每次都重新建立连接。
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原文链接：https://blog.csdn.net/qq_65168354/article/details/129168808

C3P0连接池

第一步：添加jar包

• c3p0-0.9.1.2.jar
• mysql-connector-java-5.0.8-bin.jar

第二步：在src下创建C3P0的配置文件c3p0-config.xml

<?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/test0222</property><property name="user">root</property><property name="password">root</property><property name="initialPoolSize">15</property><property name="maxIdleTime">40</property><property name="maxPoolSize">150</property><property name="minPoolSize">20</property></default-config>
</c3p0-config>

第三步：编写操作C3P0的工具类C3P0Util

package com.etime1;import com.mchange.v2.c3p0.ComboPooledDataSource;import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class C3P0Util {//创建数据库连接池private static DataSource dataSource = new ComboPooledDataSource();public  static DataSource getDataSource(){return dataSource;}//创建连接public static Connection getConnection(){try {return dataSource.getConnection();} catch (SQLException e) {throw new RuntimeException("获取数据库连接失败");}}//释放连接public static void release(Connection connection, Statement statement, ResultSet resultSet) {if (resultSet != null) {try {resultSet.close();} catch (Exception e) {e.printStackTrace();}resultSet = null;}if (statement != null) {try {statement.close();} catch (Exception e) {e.printStackTrace();}statement = null;}if (connection != null) {try {connection.close();} catch (Exception e) {e.printStackTrace();}connection = null;}}
}

第四步：使用C3P0

(1)、在数据库中建立membershipcard表并插入数据

mysql> CREATE TABLE membershipcard (id int primary key auto_increment, username varchar(40),password varchar(40), email varchar(40), birthday date 
);-- 插入数据
INSERT INTO membershipcard (username,password,email,birthday) VALUES ("lili","abc123","lili@sina.com","1999-08-14");
INSERT INTO membershipcard (username,password,email,birthday) VALUES ("koko","efg456","koko@sohu.com","1998-07-15");
INSERT INTO membershipcard (username,password,email,birthday) VALUES ("mbmb","mnb333","mbmb@sina.com","1997-06-16");
INSERT INTO membershipcard (username,password,email,birthday) VALUES ("zxzx","poi666","zxzx@sohu.com","1996-05-17");

(2)、编写JavaBean即Membershipcard

package com.etime1;
import java.util.Date;public class Membershipcard {private int id;private String username;private String password;private String email;private Date birthday;public Membershipcard() {}public Membershipcard(int id, String username, String password, String email, Date birthday) {this.id = id;this.username = username;this.password = password;this.email = email;this.birthday = birthday;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Date getBirthday() {return birthday;}public void setBirthday(Date birthday) {this.birthday = birthday;}@Overridepublic String toString() {return "[id=" + id + ", username=" + username + ", password=" + password + ", email=" + email+ ", birthday=" + birthday + "]";}
}

(3)、在JDBC中使用C3P0

package com.etime1;import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;public class Test02 {public static void main(String[] args) throws Exception {getSelect();}public static void getSelect() throws Exception{Connection connection = C3P0Util.getConnection();String sql = "select * from membershipcard";PreparedStatement preparedStatement = connection.prepareStatement(sql);ResultSet resultSet = preparedStatement.executeQuery();while (resultSet.next()){int id = resultSet.getInt(1);String username = resultSet.getString(2);String password = resultSet.getString(3);String email = resultSet.getString(4);Date birthday = resultSet.getDate(5);Membershipcard membershipcard = new Membershipcard(id, username, password, email, birthday);System.out.println(membershipcard);}}
}