Cause: java.lang.ClassNotFoundException:Cannot find class:com.mysql.cj.jdbc.Driver

最新推荐文章于 2023-01-17 01:18:52 发布

lixiaoping666

最新推荐文章于 2023-01-17 01:18:52 发布

阅读量6.3k

点赞数 12

文章标签： mybatis

本文链接：https://blog.youkuaiyun.com/lixiaoping666/article/details/105612062

版权

使用IDEA 的maven项目，实现mybatis的入门案例
mybatis的主配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--mybatis的主配置文件-->
<configuration>
    <!--配置环境-->
    <environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">
            <!--配置事务的类型-->
            <transactionManager type="JDBC"/>
            <!--配置数据源（连接池）-->
            <dataSource type="POOLED">
                <!--配置连接数据库的4个基本信息 -->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy_mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!--指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件-->
    <mappers>
        <mapper resource="com/itheima/dao/UserDao.xml"/>
    </mappers>
</configuration>

pom.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com itheima</groupId>
    <artifactId>day01_easy_01mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>

        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.32</version>

        </dependency>

        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>

        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
            <scope>test</scope>
        </dependency>



    </dependencies>


</project>

mapper配置文件 sql映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.itheima.dao.UserDao">
    <!--配置查询所有-->
    <select id="findAll" resultType="com.itheima.domain.User">
        select * from user；
    </select>

</mapper>

测试类

package com.itheima.test;

import com.itheima.dao.UserDao;
import com.itheima.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;


import java.io.IOException;
import java.io.InputStream;
import java.util.List;

/**
 * @author 黑马程序员
 * @Company http://www.ithiema.com
 * mybatis的入门案例
 */
public class MybatisTest {

    /**
     * 入门案例
     * @param args
     */
    public static void main(String[] args) throws Exception {
        //1.读取配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.创建SqlSessionFactory工厂
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        //3.使用工厂生产SqlSession对象
        SqlSession session = factory.openSession();
        //4.使用SqlSession创建Dao接口的代理对象
        UserDao userDao = session.getMapper(UserDao.class);
        //5.使用代理对象执行方法
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
        }
        //6.释放资源
        session.close();
        in.close();
    }
}

执行报错

Cause: java.lang.ClassNotFoundException:Cannot find class:com.mysql.jdbc.Driver

分析过程
1.首先思考，MySQL版本与驱动版本不符合
我的MySQL版本为 8.0.19
而我导入的mysql-connector-java包为5.1.32包，于是将mysql-connector-java包改为8.0.19

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>

继续执行，还是报相同的错，因为高版本MySQL，url后面要加时区，修改配置文件

<dataSource type="POOLED">
                <!--配置连接数据库的4个基本信息-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy_mybatis?serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>

还是报相同的错，于是又继续摸索，对照网上的配置文件修改
终于发现了一处不一样的，于是我修改自己的配置文件
原配置文件

<environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">

我将mysql改成development

<environments default="development">
        <!--配置mysql的环境-->
        <environment id="mysql">

终于不报上一个错

Cause: java.lang.ClassNotFoundException:Cannot find class:com.mysql.jdbc.Driver

但是又报空指针异常，心态崩了

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error opening session.  Cause: java.lang.NullPointerException

于是又一通查找，终于发现解决这个问题的答案

Mybatis获取SqlSession时报空指针错误解决
于是我又改回原来的配置

<environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">

但第一个错又冒出来了，我冷静分析，思考找不到驱动异常应该是包没导入到位，虽然pom.xml文件上没有报错，但应该是有其他地方没搞好。于是我开始思考，怎样包才算导入到位了，于是又找到了这篇答案
Intellij IDEA 中如何查看maven项目中所有jar包的依赖关系图
我在IDEA界面上点击Maven Projects ，发现没有Dependencies,终于找到原因了，包没有导入到位，于是我Reimport All Maven Projects.

重新运行解决问题

2020-04-19 11:13:00,790 29     [           main] DEBUG source.pooled.PooledDataSource  - PooledDataSource forcefully closed/removed all connections.
2020-04-19 11:13:00,790 29     [           main] DEBUG source.pooled.PooledDataSource  - PooledDataSource forcefully closed/removed all connections.
2020-04-19 11:13:00,790 29     [           main] DEBUG source.pooled.PooledDataSource  - PooledDataSource forcefully closed/removed all connections.
2020-04-19 11:13:00,790 29     [           main] DEBUG source.pooled.PooledDataSource  - PooledDataSource forcefully closed/removed all connections.
2020-04-19 11:13:00,899 138    [           main] DEBUG ansaction.jdbc.JdbcTransaction  - Opening JDBC Connection
2020-04-19 11:13:03,317 2556   [           main] DEBUG source.pooled.PooledDataSource  - Created connection 1163619825.
2020-04-19 11:13:03,317 2556   [           main] DEBUG ansaction.jdbc.JdbcTransaction  - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@455b6df1]
2020-04-19 11:13:03,317 2556   [           main] DEBUG om.itheima.dao.UserDao.findAll  - ooo Using Connection [com.mysql.cj.jdbc.ConnectionImpl@455b6df1]
2020-04-19 11:13:03,333 2572   [           main] DEBUG om.itheima.dao.UserDao.findAll  - ==>  Preparing: select * from user 
2020-04-19 11:13:03,442 2681   [           main] DEBUG om.itheima.dao.UserDao.findAll  - ==> Parameters: 
2020-04-19 11:13:03,849 3088   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==    Columns: id, username, birthday, sex, address
2020-04-19 11:13:03,880 3119   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 41, 老王, 2018-02-27 17:47:08, 男, 北京
2020-04-19 11:13:03,880 3119   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 42, 小二王, 2018-03-02 15:09:37, 女, 北京金燕龙
2020-04-19 11:13:03,896 3135   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 43, 小二王, 2018-03-04 11:34:34, 女, 北京金燕龙
2020-04-19 11:13:03,896 3135   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 45, 传智播客, 2018-03-04 12:04:06, 男, 北京金燕龙
2020-04-19 11:13:03,896 3135   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 46, 老王, 2018-03-07 17:37:26, 男, 北京
2020-04-19 11:13:03,896 3135   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==        Row: 48, 小马宝莉, 2018-03-08 11:44:00, 女, 北京修正
2020-04-19 11:13:03,896 3135   [           main] DEBUG om.itheima.dao.UserDao.findAll  - <==      Total: 6
User{id=41, username='老王', birthday=Tue Feb 27 17:47:08 CST 2018, sex='男', address='北京'}
User{id=42, username='小二王', birthday=Fri Mar 02 15:09:37 CST 2018, sex='女', address='北京金燕龙'}
User{id=43, username='小二王', birthday=Sun Mar 04 11:34:34 CST 2018, sex='女', address='北京金燕龙'}
User{id=45, username='传智播客', birthday=Sun Mar 04 12:04:06 CST 2018, sex='男', address='北京金燕龙'}
User{id=46, username='老王', birthday=Wed Mar 07 17:37:26 CST 2018, sex='男', address='北京'}
User{id=48, username='小马宝莉', birthday=Thu Mar 08 11:44:00 CST 2018, sex='女', address='北京修正'}
2020-04-19 11:13:04,068 3307   [           main] DEBUG ansaction.jdbc.JdbcTransaction  - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@455b6df1]
2020-04-19 11:13:04,068 3307   [           main] DEBUG ansaction.jdbc.JdbcTransaction  - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@455b6df1]
2020-04-19 11:13:04,068 3307   [           main] DEBUG source.pooled.PooledDataSource  - Returned connection 1163619825 to pool.