狂神Mybatis笔记

Mybatis

1.简介

什么是 MyBatis？

1.MyBatis 是一款优秀的持久层框架

2.它支持自定义 SQL、存储过程以及高级映射

3.MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作

4.MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java

POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

中文文档: https://mybatis.org/mybatis-3/zh/sqlmap-xml.html
Github: https://github.com/search?q=mybatis

2.创建一个Mybatis程序

2.1搭建环境

搭建数据库

create database mybatis;
use mybatis;

create table user(
 id int(20) not null primary key,
 name varchar(30) default null,
 pwd  varchar(30) default null
)engine=innodb default charset=utf8;

insert into user (id,name,pwd) values 
(1,'k','123456'),
(2,'z','123456')

创建Maven项目 （父工程）

1.删除src
2.Maven配置文件导入依赖
3.在父工程下导入依赖（子工程均可使用）

 <!--导入依赖-->
      <dependencies>
        <!--    mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.28</version>
        </dependency>
        <!--        mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--        junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

创建子工程

maven由于他的约定大于配置，解决配置文件无法被导出或者生效的问题，子工程Maven配置文件中导入 在父工程导入是没用的

    <build>
        <resources>
            <!--        手动指定java文件夹为resources文件夹-->
            <!--        当xml文件在java文件夹而不在resources文件夹时，该xml文件不能被编译进target目录，-->
            <!--        又因为代码在执行时是执行的target中编译过的文件，所以加载不到该xml文件。因此必须进行指定。-->
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <!--                    指定java文件夹下子包中的所有.xml文件-->
                    <include>**/*.xml</include>
                </includes>
            </resource>

            <!--            上述的指定是将原有的编译资源resources目录覆盖掉了，而不是添加编译目录，因此需要补充原有的编译资源目录-->
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.*</include>
                </includes>
            </resource>

        </resources>
    </build>

2.2编写mybatis.config核心配置文件

<?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">
<!--核心配置文件-->
<configuration>
    <!--    环境               开发者-->
    <environments default="development">
        <environment id="development">
            <!--            事务管理-->
            <transactionManager type="JDBC"/>
            <!--            数据源-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf8&amp;useSSL=false&amp;serverTimezone=UTC&amp;rewriteBatchedStatements=true&amp;allowPublicKeyRetrieval=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <!--   每一个Mapper.xml都需要在Mybatis核心文件配置中注册 -->
    <mappers>
        <mapper resource="com/kz/dao/UserMapper.xml"/>
    </mappers>
</configuration>

2.3编写mybatis工具类

package com.kz.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;

//sqlSessionFactory --> sqlSession
public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
       //获取sqlSession对象
    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = null;
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 //SqlSession 完全包含了面向数据库执行SQL命令所需的所有方法
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

}

2.4编写实体类

package com.kz.pojo;

public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public int getId() {
        return id;
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

2.5编写Dao接口

public interface UserMapper{
    //查询
    public List<User> getUserList();
}

2.6编写Mapper(相当于JDBC的Dao接口的实现类)

<?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">
                <!--绑定一个Mapper接口-->
<mapper namespace="com.kz.dao.UserMapper">
<!--      返回     方法名                          实体类   -->
    <select id="getUserList" resultType="com.kz.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

3.测试

规范写法

    @Test
    public void getUserList(){
        //获取sqlSession对象
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        // 方式1: getMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User user:userList
             ) {
            System.out.println(user);
        }

        //关闭
        sqlSession.close();
    }

4.添加功能

4.1增删改操作 必须提交事务

注意事项!!!

id:就是对应namespace中的方法名
resultTyoe:Sql执行的返回类型
parameterTyoe:参数类型

1.编写接口

//添加
   public int addUser(User user);

2.编写对应的mapper中的sql语句

   <!--        方法名                 输入类型 -->
   <insert id="addUser" parameterType="com.kz.pojo.User">
       insert into  mybatis.user (id,name,pwd)  value (#{id},#{name},#{pwd});
   </insert>

3.测试

//增删改必须提交事务
   @Test
   public void addUser(){
       //获取sqlSession
       SqlSession sqlSession = MyBatisUtils.getSqlSession();
       //获取接口
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       int insert = mapper.addUser(new User(4, "张国荣", "123456"));
       //事务提交
       sqlSession.commit();
       sqlSession.close();
   }

4.2编写接口

public interface UserMapper {
    //查询
    public List<User> getUserList();
    //通过id查询
    public User selectById(int i);
    //添加
    public int addUser(User user);
    //修改
    public int updateUser(User user);
    //删除
    public int deleteUser(int i);
    //万能map
    int addUser2(Map<String,Object> map);
    //模糊查询
    List<User> selectLike(String value);
}

4.3编写对应的mapper中的sql语句

<?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">
                <!--绑定一个Mapper接口-->
<mapper namespace="com.kz.dao.UserMapper">
<!--      返回     方法名                          实体类   -->
    <select id="getUserList" resultType="com.kz.pojo.User">
        select * from mybatis.user
    </select>
<!--                         输入类型             输出类型-->
    <select id="selectById" parameterType="int" resultType="com.kz.pojo.User">
        select * from mybatis.user where id=#{id};
    </select>
    <!--                         输入类型             输出类型-->
    <insert id="addUser" parameterType="com.kz.pojo.User">
        insert into  mybatis.user (id,name,pwd)  value (#{id},#{name},#{pwd});
    </insert>

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

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

    <insert id="addUser2" parameterType="map">
        insert into mybatis.user (id,name,pwd) values (#{uid},#{uname},#{upwd})
    </insert>

    <select id="selectLike" parameterType="map" resultType="com.kz.pojo.User">
        select * from mybatis.user where name like "%"#{value}"%";
    </select>
</mapper>

测试

package com.kz.dao;

import com.kz.pojo.User;
import com.kz.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class UserMapperTest {
    @Test
    public void getUserList(){
        //获取sqlSession对象
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        // 方式1: getMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User user:userList
             ) {
            System.out.println(user);
        }

        //关闭
        sqlSession.close();
    }
    @Test
    public void selectById(){
        //获取SqlSessiion
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        //获取接口
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        User user = mapper.selectById(2);
        System.out.println(user);
        sqlSession.close();
    }
//万能的Map
   @Test
   public void addUser2(){
       SqlSession sqlSession = MyBatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       Map<String, Object> objectStringMap = new HashMap<>();
       objectStringMap.put("uid",10);
       objectStringMap.put("uname","123");

       mapper.addUser2(objectStringMap);

       sqlSession.commit();
       sqlSession.close();

   }
//模糊查询
    @Test
    public void selectLike(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = mapper.selectLike("1");
        for (User user : users) {
            System.out.println(user);
        }

        sqlSession.close();
    }
    //增删改必须提交事务
    @Test
    public void addUser(){
        //获取sqlSession
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        //获取接口
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int insert = mapper.addUser(new User(4, "张国荣", "123456"));
        //事务提交
        sqlSession.commit();
        sqlSession.close();
    }


  @Test
    public void updateUser(){
      SqlSession sqlSession = MyBatisUtils.getSqlSession();
      UserMapper mapper = sqlSession.getMapper(UserMapper.class);
      int i = mapper.updateUser(new User(1, "刘德华", "123456"));

      sqlSession.commit();
      System.out.println("修改成功");
      sqlSession.close();
  }

   @Test
    public void deleteUser(){
       SqlSession sqlSession = MyBatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       int i = mapper.deleteUser(4);

       sqlSession.commit();
       System.out.println("删除成功");
       sqlSession.close();
   }


}

5.分析错误

1.标签不要匹配错

2.resouce绑定mapper，需要使用路径

3.程序配置文件必须符合规范

4.NullPoinException，没有注册资源

5.输出的xml文件中存在中文乱码

6.maven资源没有导出问题