[Java知识库]【C3P0】解决使用c3p0数据库连接池的各种报错警告: Having failed to acquire a resource com.mchange.v2.resourcepool

运行环境
工具： IntelliJ IDEA
java version “1.8.0_261”
MySQL"5.7.19"
在使用IDEA连接c3p0数据库时，导入的四个jar包：
1.mysql-connector-java-5.1.47.jar
2.c3p0-0.9.5.5.jar
3.mchange-commons-java-0.2.20.jar
4.commons-logging-1.2.jar

c3p0-config.xml配置文件如下：

<?xml version="1.0" encoding="UTF-8" ?>
        <c3p0-config>
        <!--
        c3p0的缺省（默认）配置
        如果在代码中"ComboPooledDataSource ds=new ComboPooledDataSource("");"这样写就表示使用的是C3P0的缺省（默认）配置信息来创建数据源-->
        <default-config>
                <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
                <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=false</property>
                <property name="user">root</property>
                <property name="password">123456</property>

                <property name="acquireIncrement">5</property>
                <property name="initialPoolSize">10</property>
                <property name="minPoolSize">5</property>
                <property name="maxPoolSize">20</property>
        </default-config>




        <!--
        c3p0的命名配置
        如果在代码中"ComboPooledDataSource ds=new ComboPooledDataSource("MySQL");"这样写就表示使用的是name是MySQL的配置信息来创建数据源-->
        <name-config name="MySQL">
        <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=false&amp;serverTimezone=UTC</property>
        <property name="user">root</property>
        <property name="password">123456</property>

        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">10</property>
        <property name="minPoolSize">5</property>
        <property name="maxPoolSize">20</property>
        </name-config>
        </c3p0-config>

测试代码（TestC3P0）：

package com.yuanye.lesson05;

import com.yuanye.lesson05.utils.JdbcUtils_C3P0;


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

public class TestC3P0 {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement st = null;

        try {
            conn = JdbcUtils_C3P0.getConnection();//原来是自己实现的，现在用别人实现的

            //区别
            //使用？占位符代替参数
            String sql = "insert into users(id,`name`,`password`,`email`,`birthday`) values(?,?,?,?,?)";

            st = conn.prepareStatement(sql);//()需要参数，预编译SQL,先写sql，然后不执行

            //手动给参数赋值
            st.setInt(1,6);//给id赋值
            st.setString(2,"yuanye4");
            st.setString(3,"123456");
            st.setString(4,"123456@qq.com");
            //注意点：sql.Date  数据库用的
            //      util.Date  JAVA用的  new Date().getTime()获得时间戳
            st.setDate(5,new java.sql.Date(new java.util.Date().getTime()));

            //执行
            int i = st.executeUpdate();
            if (i>0){
                System.out.println("插入成功！");
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            JdbcUtils_C3P0.release(conn,st,null);
        }
    }
}

执行成功结果如下：

D:\Java\jdk1.8.0_261\bin\java.exe "-javaagent:D:\IntelliJ IDEA Community Edition 2021.1\lib\idea_rt.jar=8451:D:\IntelliJ IDEA Community Edition 2021.1\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_261\jre\lib\charsets.jar;D:\java\jdk1.8.0_261\jre\lib\deploy.jar;D:\java\jdk1.8.0_261\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_261\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_261\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_261\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_261\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_261\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_261\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_261\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_261\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_261\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_261\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_261\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_261\jre\lib\javaws.jar;D:\java\jdk1.8.0_261\jre\lib\jce.jar;D:\java\jdk1.8.0_261\jre\lib\jfr.jar;D:\java\jdk1.8.0_261\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_261\jre\lib\jsse.jar;D:\java\jdk1.8.0_261\jre\lib\management-agent.jar;D:\java\jdk1.8.0_261\jre\lib\plugin.jar;D:\java\jdk1.8.0_261\jre\lib\resources.jar;D:\java\jdk1.8.0_261\jre\lib\rt.jar;D:\java练习\jdbcStudy\out\production\jdbcStudy;D:\java练习\jdbcStudy\lib\c3p0-0.9.5.5.jar;D:\java练习\jdbcStudy\lib\commons-dbcp2-2.9.0.jar;D:\java练习\jdbcStudy\lib\commons-logging-1.2.jar;D:\java练习\jdbcStudy\lib\commons-pool2-2.11.1.jar;D:\java练习\jdbcStudy\lib\mchange-commons-java-0.2.20.jar;D:\java练习\jdbcStudy\lib\mysql-connector-java-5.1.47.jar com.yuanye.lesson05.TestC3P0
十月 22, 2021 9:12:49 下午 com.mchange.v2.log.MLog 
信息: MLog clients using java 1.4+ standard logging.
十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.C3P0Registry 
信息: Initializing c3p0-0.9.5.5 [built 11-December-2019 22:07:46 -0800; debug? true; trace: 10]
十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.cfg.C3P0Config 
警告: named-config with name 'MySQL' does not exist. Using default-config.
十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.cfg.C3P0Config 
警告: named-config with name 'MySQL' does not exist. Using default-config extensions.
十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 5, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> MySQL, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.cj.jdbc.Driver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 2rvxttak1anfh8q1k3ken4|77a567e1, idleConnectionTestPeriod -> 0, initialPoolSize -> 10, jdbcUrl -> jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&characterEncoding=utf8&useSSL=false, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

十月 22, 2021 9:12:50 下午 com.mchange.v2.c3p0.DriverManagerDataSource 
警告: Could not load driverClass com.mysql.cj.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:143)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:173)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

插入成功！

Process finished with exit code 0

结论：

这是我经过各种报错后查阅各种资料和广大网友的相关问题后总结出来的MySQL8之后连接C3P0的正确配置文件和代码。
如果网友们有相关问题，一定要检查开发环境和MySQL不同版本之间的兼容性。
基本上都是以下

        <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=false&amp;serverTimezone=UTC</property>

这一段代码的useSSL问题和时区问题！
如果出现Could not initialize class 那么还要导入一个文章开头所提到的第四个包：commons-logging-1.2.jar 的依赖！