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namespace 中的包名要和 Dao/Mapper 接口的包名一致

select：选择，查询语句

同理，还有 insert、update、delete 标签

id：对应的 namespace 中的方法名

resultType：sql 语句执行的返回值

parameterType：参数类型

先在 mysql 建表（id、name、pwd）

配置 Maven 环境（mysql、mybatis、junit）

MybatisUtils.java：

package com.demo.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 MybatisUtils {private static SqlSessionFactory sqlSessionFactory;static {try {//获取sqlSessionFactory对象String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) {e.printStackTrace();}}/*有了SqlSessionFactory，就可以获得SqlSession的实例SqlSession提供了在数据库执行SQL命令所需的所有方法可以通过SqlSession实例来执行已映射的SQL语句*/public static SqlSession getSqlSession(){return sqlSessionFactory.openSession();}
}

mybatis-config.xml：（resources 目录下）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><!-- configuration核心配置文件 -->
<configuration><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/><property name="username" value="root"/><property name="password" value="root"/></dataSource></environment></environments><!-- 每一个Mapper.xml都需要在Mybatis核心配置文件中注册 --><mappers><mapper resource="com/demo/dao/UserMapper.xml"/></mappers></configuration>

 User.java：

package com.demo.pojo;
//实体类
public class User {private int id;private String name;private String pwd;//无参构造public User() {}//有参构造public User(int id, String name, String pwd) {this.id = id;this.name = name;this.pwd = pwd;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", pwd='" + pwd + '\'' +'}';}
}

UserMapper 接口：

package com.demo.dao;import com.demo.pojo.User;import java.util.List;public interface UserMapper {//查询全部用户List<User> getUserList();//根据ID查询用户User getUserById(int id);//insert插入用户int addUser(User user);//update修改用户int updateUser(User user);//delete删除用户int deleteUser(int id);
}

UserMapper.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.demo.dao.UserMapper"><!-- select 查询语句 --><select id="getUserList" resultType="com.demo.pojo.User">select * from mybatis.user</select><select id="getUserById" parameterType="int" resultType="com.demo.pojo.User">select * from mybatis.user where id = #{id}</select><!-- insert插入数据，对象中的属性可以直接取出来 --><insert id="addUser" parameterType="com.demo.pojo.User">insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd});</insert><!-- update更新数据 --><update id="updateUser" parameterType="com.demo.pojo.User">update mybatis.user set name = #{name}, pwd = #{pwd} where id = #{id};</update><!-- delete删除数据 --><delete id="deleteUser" parameterType="int">delete from mybatis.user where id = #{id};</delete></mapper>

UserDaoTest.java：（test 目录下）

package com.demo.dao;import com.demo.pojo.User;
import com.demo.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;import java.util.List;public class UserDaoTest {//查询全部@Testpublic void test(){//获得SqlSession对象SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.getUserList();for(User user : userList){System.out.println(user);}//关闭sqlSessionsqlSession.close();}//根据id查询@Testpublic void getUserById(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user = mapper.getUserById(1);System.out.println(user);sqlSession.close();}//增删改需要提交事务//添加数据@Testpublic void addUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.addUser(new User(4, "张三4", "123"));//提交事务sqlSession.commit();sqlSession.close();}//修改数据@Testpublic void updateUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.updateUser(new User(4,"李四","111"));sqlSession.commit();sqlSession.close();}//删除数据@Testpublic void deleteUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.deleteUser(4);sqlSession.commit();sqlSession.close();}
}

总结：

1.编写接口

2.编写对应的 Mapper 中的 sql 语句

3.测试

select：

    <select id="getUserById" parameterType="int" resultType="com.demo.pojo.User">select * from mybatis.user where id = #{id}</select>

 insert：

    <insert id="addUser" parameterType="com.demo.pojo.User">insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd});</insert>

update：

    <update id="updateUser" parameterType="com.demo.pojo.User">update mybatis.user set name = #{name}, pwd = #{pwd} where id = #{id};</update>

delete：

    <delete id="deleteUser" parameterType="int">delete from mybatis.user where id = #{id};</delete>

注意：增删改需要提交事务