1.搭建数据库(我用的是mysql 5.5)

#创建一个mybatis数据库create database `mybatis`; #使用mybatis数据库use `mybatis`; #创建一个user表，有id、username、password三个字段create table `user`( `id` int(10) not null primary key auto_increment, `username` varchar(30) default null, `password` varchar(30) default null)engine=InnoDB default charset=utf8; #插入数据insert into `user`（`username`,`password`） values('张三'，123456)，('李四'，123456)，('王五'，123456)；

2.导入mybatis相关的jar包（COPY，建议创建一个父子项目）

<dependencies> <dependency><!--mysql依赖包--> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.19</version> </dependency><!--mybatis依赖包--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.2</version> </dependency><!--junit依赖包,为什么要用junit依赖包？@Test做单元测试用的--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> </dependencies> <!--maven静态资源过滤问题：配置报错，不设置会报错：ExceptionInInitializerError--> <build> <resources> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>true</filtering> </resource> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>true</filtering> </resource> </resources></build>

3.编写MyBatisUtil工具类（COPY，低层原理还没有搞懂，直接复制的条件是要创建一个mybatis-config.xml文件 文件名要一致）

package com.kuang.utils; 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; public class MybatisUtil { private static SqlSessionFactory sqlSessionFactory; static{ try { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); //SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);因为重复定义导致空指针异常 sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { e.printStackTrace(); } } public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession(); } }

4.1编写db.properties配置文件（COPY，是后来优化的）

driver=com.mysql.cj.jdbc.Driverurl=jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghaiusername=rootpassword=root

4.2编写MyBatis核心配置文件（COPY，mybatis-config.xml，已优化）

<?xml version="1.0" encoding="UTF8" ?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"><!--第一个问题：com.mysql.jdbc.Driver和mysql-connector-java 5一起用。com.mysql.cj.jdbc.Driver和mysql-connector-java 6+ 一起用。第二个问题：serverTimezone=Asia/Shanghai 要加时区，不加时区会报错--> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${passwprd}"/> </dataSource> </environment> </environments> <mappers> <mapper resource="com/super/dao/UserMapper.xml"/> </mappers></configuration>

5.编写User实体类

public class User { private int id; //id private String name; //姓名 private String pwd; //密码 //构造,有参,无参 //set/get //toString() }

6.编写Mapper接口类(Mapper.java)

package com.kuang.dao; import com.kuang.pojo.User; import java.util.List; public interface Mapper { List<User> getUserList();}

7.编写mapper.xml配置文件

<?xml version="1.0" encoding="UTF8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.super.dao.UserDao"> <select id="getUserList" resultType="com.kuang.pojo.User"> select * from mybatis.user; </select></mapper>

8.编写测试类

package com.kuang.dao; import com.kuang.pojo.User;import com.kuang.utils.Mybatise;import org.apache.ibatis.session.SqlSession;import org.junit.Test; import java.util.List; public class UserDaoTest { @Test public void test(){ SqlSession sqlSession = MybatisUtil.getSqlSession(); UserDao mapper = sqlSession.getMapper(Mapper.class); List<User> userList = mapper.getUserList(); for(User user:userList){ System.out.println(user); } //sqlSession.commit();增删改需要添加事务 sqlSession.close(); }}

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