1.在pom.xml文件中导入jar包同时不要忘记jdbc包，否则会报错

<dependency><groupId>com.mchange</groupId><artifactId>c3p0</artifactId><version>0.9.5.2</version></dependency>
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.17</version></dependency>

2.在src目录下创建c3p0-config.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config><!--使用默认的配置读取连接池对象--><default-config><!--连接参数--><property name="driverClass">com.mysql.cj.jdbc.Driver</property><property name="jdbcUrl">jdbc:mysql://localhost:3306/db1?serverTimezone=Asia/Shanghai</property><property name="user">root</property><property name="password">root</property><!--连接池参数--><!--初始化申请的连接数量--><property name="initialPoolSize">5</property><!--超时时间--><property name="checkoutTimeout">3000</property><property name="maxIdleTime">30</property><!--最大的连接数量--><property name="maxPoolSize">10</property><property name="minPoolSize">5</property><property name="maxStatements">200</property></default-config><named-config name="mysql"><property name="acquireIncrement">50</property><property name="initialPoolSize">100</property><property name="minPoolSize">50</property><property name="maxPoolSize">1000</property><!-- intergalactoApp adopts a different approach to configuring statement caching --><property name="maxStatements">0</property><property name="maxStatementsPerConnection">5</property></named-config><named-config name="oracle"><property name="acquireIncrement">50</property><property name="initialPoolSize">100</property><property name="minPoolSize">50</property><property name="maxPoolSize">1000</property><!-- intergalactoApp adopts a different approach to configuring statement caching --><property name="maxStatements">0</property><property name="maxStatementsPerConnection">5</property></named-config>
</c3p0-config>

3.写一个类测试下

package c3p0;import com.mchange.v2.c3p0.ComboPooledDataSource;import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;public class C3P0Demo1 {public static void main(String[] args) throws SQLException {//1.创建数据库连接池对象DataSource ds = new ComboPooledDataSource();//2.获取连接对象Connection conn = ds.getConnection();//3.打印System.out.println(conn);}
}

输出下面语句表示成功！其中红色的不是报错，而是日志

4.访问其他配置文件

package c3p0;import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.junit.jupiter.api.Test;import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;public class C3P0Demo2 {public static void main(String[] args) throws SQLException {//1.获取DataSource 即连接池对象，使用默认配置DataSource ds = new ComboPooledDataSource();//2.获取连接对象/*for (int i = 1; i <=11 ; i++) {//报错，因为池子最大连接数为10Connection conn = ds.getConnection();System.out.println(i+":"+conn);}*/for (int i = 1; i <=11 ; i++) {//正确，因为归还了Connection conn = ds.getConnection();System.out.println(i+":"+conn);if (i==5){conn.close();//归还连接到连接池}}System.out.println("----------");test();}public static void test() throws SQLException {//1.1获取DataSource，使用指定名称配置DataSource ds = new ComboPooledDataSource("mysql");for (int i = 1; i <=60 ; i++) {//不报错，因为新配置的最大连接数很大Connection conn = ds.getConnection();System.out.println(i+":"+conn);}}
}