mybatis xml配置使用方式，resultMap使用

项目结构

数据库表

引入依赖

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.30</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

mybatis-config.xml 配置日志 数据源 映射

<?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>
<!--    dddd-->
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="ture"/><!--配置下划线转换为驼峰命名风格-->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager><!--事务管理器-->
            <dataSource type="POOLED"><!--数据源 POOLED代表池化-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="dao/StudentDao.xml"></mapper>
    </mappers>
</configuration>

编写实体类

package com.tmg.domain;

public class Student {
    private int id;
    private String name;
    private int age;//提供构造器
    private String email;//提供set()，get()，toString(),hascode()等方法

    public Student(int id, String name, int age, String email) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.email = email;
    }

    public Student() {
    }

    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 int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", email='" + email + '\'' +
                '}';
    }
}

控制数据库数据方法

package com.tmg.dao;

import com.tmg.domain.Student;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface StudentDao {

    void insert(Student employee);

    void update(Student employee);

    void deleteById(Long id);

    List<Student> selectAll();

    Student selectById(Long id);

    //多个参数的配置
    void insertEmp( @Param("stuName")  String name,
                   @Param("stuAge") int age, @Param("stuEmail")  String email);
}

StudentDao.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!--指定约束文件：定义和限制当前文件中可以使用的标签和属性，以及标签出现的顺序
mybatis-3-mapper.dtd 约束文件名称
-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射的命名空间 = 包名+接口类-->
<mapper namespace="com.tmg.dao.StudentDao">
    <!--配置insert操作 id是方法名 parameterType是参数类型  #{属性名}用于读取对象的属性值-->
    <!--#{}和${}的区别，#{}相当于PreparedStatement的占位符？提前编译，避免SQL注入 ${}是Statement字符串拼接，不能避免注入 -->
    <!--获得最新的自增主键值 useGeneratedKeys=true keyProperty主键的属性-->
    <insert id="insert" useGeneratedKeys="true" keyProperty="id" parameterType="com.tmg.domain.Student">
        insert into student( stu_id,stu_name,stu_age,stu_email) values (#{id},#{name},#{age},#{email});
    </insert>

    <update id="update">
        update student set stu_age=#{age},stu_email=#{email},stu_name=#{name} where stu_id=#{id} ;
    </update>

    <delete id="deleteById">
        delete from student where stu_id=#{id};
    </delete>
<!--    问题：查询出的名称为多个单词的字段出现null值-->
<!--    原因：数据库的字段单词以下划线分隔，Java的属性以驼峰命名，导致部分名称不一致无法实现映射-->
    <select id="selectAll" resultType="com.tmg.domain.Student" resultMap="student">
        select * from student
    </select>

    <resultMap id="student" type="com.tmg.domain.Student">
        <!--配置主键 property是java属性名 column是表字段名-->
        <id property="id" column="stu_id" javaType="java.lang.Integer"></id>
        <!--普通字段-->
        <result property="name" column="stu_name"></result>
        <result property="age" column="stu_age"></result>
        <result property="email" column="stu_email"></result>
    </resultMap>

    <select id="selectById" resultType="com.tmg.domain.Student">
        select * from student where stu_id=#{id}
    </select>

    <insert id="insertEmp">
        insert into student(stu_name,stu_age,stu_email) values (#{stuName},#{stuAge},#{stuEmail});
    </insert>
</mapper>

StudentDaoText 测试类

package com.tmg.dao;

import com.tmg.domain.Student;
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.util.List;

public class StudentDaoText {

    @Test
    public void testinsert() throws IOException {
        //创建会话工厂构建器
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        //创建会话
        SqlSession sqlSession = factory.openSession();
        //获得Mapper对象
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);//通过jdk动态代理创建实现类，返回代理对象
        Student student = new Student(0, "zzz", 20, "zzz@qq.com");
        mapper.insert(student);
        sqlSession.commit();
        System.out.println("insert--->"+student);


    }
    @Test
    public void testupdate() throws IOException {
        //创建会话工厂构建器
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        //创建会话
        SqlSession sqlSession = build.openSession();
        //获得Mapper对象
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        Student student = new Student(12, "zl", 99, "zl@qq.com");
        mapper.update(student);
        sqlSession.commit();
    }

    @Test
    public void testdeleteById() throws IOException {
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        mapper.deleteById(11L);
        sqlSession.commit();
    }

    @Test
    public void testselectAll() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        List<Student> students = mapper.selectAll();
        for(Student student : students){
            System.out.println(student);
        }

    }
    @Test
    public void testselectById() throws IOException {
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = factory.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        Student student = mapper.selectById(3L);
        System.out.println("student---->"+student);

    }

    @Test
    public void testinsertEmp() throws IOException {
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = factory.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        mapper.insertEmp("tmg",18,"tmg@qq.com");
        sqlSession.commit();
    }

}