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第一个mybatis
31 浏览 | 2020-01-20 | 分类:SSM | 标签:mybatis,java,数据库,SSM

简介

1. 建立一个maven项目

2. 导入jdbc mybatis 和 junit

<dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.8</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

3. 在src/main/resources中建立mybatis-config.xml文件

mybatis-config.xml文件名随意

<?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>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>

  </mappers>
</configuration>

4.编写 SqlSessionFactory(固定写法)

官网

String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

自定义

package top.wmgx.util;
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 String resource = "mybatis_config.xml"; //前面的配置文件名称
    private static InputStream inputStream;
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            inputStream= Resources.getResourceAsStream(resource);
            sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
        }
        catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

5. 编写代码

实体类

实体类设置Getter Setter方法,其中的属性与数据库一致

Mapper实现接口(DAO)

建立mappe接口

和DAO一样

建立配置文件(同目录)

<?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">
<!--绑定对应的mapper接口-->
<mapper namespace="top.wmgx.mapper.UserMapper">
<!--    id为绑定接口的方法-->
<!--    resultType为返回类型的实体类型(写全路径)-->
    <select id="getUserList" resultType="top.wmgx.pojo.User">
        select * from user
    </select>
</mapper>

namespace中文意思:命名空间,作用如下:

  1. namespace和子元素的id联合保证唯一 , 区别不同的mapper
  2. 绑定DAO接口

    • namespace的命名必须跟某个接口同名
    • 接口中的方法与映射文件中sql语句id应该一一对应
  3. namespace命名规则 : 包名+类名

在mybatis-config.xml中添加此接口的映射

    <mappers>
        <mapper resource="top/wmgx/mapper/UserMapper.xml"></mapper>
    </mappers>
<!-- 
使用映射器接口实现类的完全限定类名
需要配置文件名称和接口名称一致,并且位于同一目录下
-->
<mappers>
  <mapper class="top.wmgx.mapper.UserMapper"/>
</mappers>
<!-- 
将包内的映射器接口实现全部注册为映射器
但是需要配置文件名称和接口名称一致,并且位于同一目录下
-->
<mappers>
  <package name="top.wmgx.mapper"/>
</mappers>

调用

package top.wmgx.mapper;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import top.wmgx.pojo.User;
import top.wmgx.util.MybatisUtils;

import java.util.List;

public class UserMapperTest {
    @Test
    public void test(){
        //获取SqlSession对象
        SqlSession sqlSession= (SqlSession) MybatisUtils.getSqlSession();
        //执行SQL
        UserMapper mapper =sqlSession.getMapper(UserMapper.class);
        List<User> user=mapper.getUserList();
        System.out.printf(user.toString());
        sqlSession.close();
    }
}

6. CRUD

6.1 namespace

namespace中的包名要与mapper(Dao)接口中的包名一致

6.2 select

选择查询:

  • id:实现的方法
  • resultType 返回值类型
  • parameterType: 参数类型
  1. 编写接口

    User getUserById(int id);
  1. 配置文件

    <select id="getUser" resultType="top.wmgx.pojo.User" parameterType="int">
    select * from user where id =#{id}
    </select>

6.3 Insert

  • 需要用commit提交才可生效
  1. 编写接口

    int addUser(User user);
  1. 配置文件

     <insert id="addUser" parameterType="top.wmgx.pojo.User">
            insert into user (id,name,pwd) values(#{id},#{name},#{pwd})
    </insert>
  2. 测试

    @Test
    public void insertUserTest(){
            //获取SqlSession对象
            SqlSession sqlSession= (SqlSession) MybatisUtils.getSqlSession();
            UserMapper mapper =sqlSession.getMapper(UserMapper.class);
            User u = new User(4,"abc","12345");
            mapper.addUser(u);
            sqlSession.commit();
            sqlSession.close();
    }

6.4 Update

  • 需要用commit提交才可生效
  1. 编写接口

    int updateUser(User user);
  2. 配置文件

    <update id="updateUser" parameterType="top.wmgx.pojo.User">
            update user set name= #{name},pwd=#{pwd} where id=#{id}
    </update>
  3. 测试

    @Test
    public void insertUserTest(){
            //获取SqlSession对象
            SqlSession sqlSession= (SqlSession) MybatisUtils.getSqlSession();
            UserMapper mapper =sqlSession.getMapper(UserMapper.class);
            User u = new User(4,"eas","54321");
            mapper.addUser(u);
            sqlSession.commit();
            sqlSession.close();
    }

6.5 Delete

  • 需要用commit提交才可生效
  1. 编写接口

    int deleteUser(int id);
  1. 配置文件

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

学习视频https://www.bilibili.com/video/av69742084

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