Mybatis快速入门的代码实现及报错处理解决org.apache.ibatis.exceptions.PersistenceException

2024-04-03 14:55:22

开发步骤：

创建普通的maven项目，导入mybatis坐标和其他的相关坐标

<!--mybatis坐标-->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.4.5</version>
</dependency>
<!--mysql驱动坐标-->
<dependency>    
    <groupId>mysql</groupId>   
    <artifactId>mysql-connector-java</artifactId>    
    <version>5.1.6</version>    
    <scope>runtime</scope>
</dependency>
<!--单元测试坐标-->
<dependency>    
    <groupId>junit</groupId>    
    <artifactId>junit</artifactId>    
    <version>4.12</version>    
    <scope>test</scope>
</dependency>
<!--日志坐标-->
<dependency>    
    <groupId>log4j</groupId>    
    <artifactId>log4j</artifactId>    
    <version>1.2.12</version>
</dependency>

在数据库中创建user表

创建User实体类


public class User {
    private int id;
    private String username;
    private String password;

	//省略了getter和setter方法
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

创建映射文件UserMapper.xml

查询出的结果集封装到resultType实体对象

<?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="userMapper">
<!--命名空间+id组成了测试类里的执行操作的参数-->
    <select id="findAll" resultType="com.itheima.domain.User">
		select * from User
	</select>
</mapper>

编写mybatis核心文件sqlMapConfig.xml

记得根据自己的数据库修改以下文件中的数据库信息：

<?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">
<configuration>
        <!--数据源环境-->
	<environments default="development">
		<environment id="development">
        <!--事务管理器jdbc-->
			<transactionManager type="JDBC"/>
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver"/>
				<property name="url" value="jdbc:mysql://localhost:3306/test"/>
				<property name="username" value="root"/>
				<property name="password" value="root"/>
			</dataSource>
		</environment>
	</environments>
		<!--加载映射文件-->
	<mappers>
		<mapper resource="com/itheima/mapper/UserMapper.xml"/>
	</mappers>
</configuration>

编写测试代码

package com.itheima.test;

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 org.junit.Test;

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

public class MybatisTest {
    @Test
    public void test1() throws IOException {
        //加载核心配置文件
InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
//获得sqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new            
                           SqlSessionFactoryBuilder().build(resourceAsStream);
//获得sqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession();
//执行sql语句
List<User> userList = sqlSession.selectList("userMapper.findAll");
//打印结果
System.out.println(userList);
//释放资源
sqlSession.close();

    }
}

常见报错

如果遇到错误org.apache.ibatis.exceptions.PersistenceException: ### Error querying database.
Cannot find class: com.mysql.jdbc.Driver
先看一下自己driver驱动书写是否正确，如果书写正确那就是mysql坐标的问题，我更换了mysql坐标的版本再运行可以了。

码农公寓