mybatis 学习一

一：首先创建一个普通的maven项目。接着删掉src目录，接着在pom.xml下导入maven依赖

 <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
<!--            <version>5.1.46</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>

        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>


    </dependencies>


    <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

二：在该maven项目下创建子模块，该子模块会继承父模块的maven依赖，紧接着在该子模块下在resources目录下创建该模块的核心配置文件mybatis-config.xml

<?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="com.mysql.jdbc.Driver"/>-->
<!--                <property name="url" value="jdbc:mysql://localhost:3306/mybatisdb?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatisdb?useSSL=false&amp;serverTimezone=Asia/Shanghai
                &amp;zeroDateTimeBehavior=CONVERT_TO_NULL
                &amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/dong/dao/UserMapper.xml"></mapper>
    </mappers>

</configuration>

三：在main/java目录下创建com.dong.dao/pojo/utils 三个包。

其中utils包目录下创建MybatisUtils.java ，表示为mybatis工具类

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            //使用Mybatis第一步：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();
        }
    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

pojo包存放实体类，例如：

public class User {

    private int id;
    private String name;
    private String pwd;

}

dao包存放*Mapper.java 接口，这相当于javaWeb的Dao接口。

并且还存放了*Mapper.xml ，这相当于JavaWeb的Dao实现类。

例如：

package com.dong.dao;

import com.dong.pojo.User;

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

/**
 * @author dong
 * @create 2020-02-25 10:26
 */
public interface UserMapper {

    //模糊查询
    List<User> getUserLike(String value);

    //查询所以用户
    List<User> getUserList();

    //根据ID查询用户
    User getUserById(int id);

    //insert一个用户
    int addUser(User user);

    //万能map
    int addUser2(Map<String,Object> map);

    //修改用户
    int updateUser(User user);

    //删除用户
    int deleteUser(int id);



}

该接口的方法名为xml实现语句的id

<?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">

<mapper namespace="com.dong.dao.UserMapper">

    <!--模糊查询-->
    <select id="getUserLike" resultType="com.dong.pojo.User">
        select * from mybatisdb.user where name like #{value}
    </select>

    <select id="getUserList" resultType="com.dong.pojo.User">
    select * from mybatisdb.user
  </select>

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

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

    <insert id="addUser2" parameterType="map">
        insert into mybatisdb.user (id, name, pwd) values (#{userId},#{userName},#{password});
    </insert>

    <!--呵呵-->
    <update id="updateUser" parameterType="com.dong.pojo.User">
        update mybatisdb.user set name = #{name},pwd=#{pwd} where id=#{id};
    </update>

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


</mapper>

每个*Mapper.xml文件的namespace=绑定一个对应的mapper接口。创建完Mapper后，需要在子模块的核心配置文件mybatis-config.xml文件中注册mappers。

 <mapper resource="com/dong/dao/*Mapper.xml"></mapper>

四，测试：

public class UserDaoTest {

    @Test
    public void test(){
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try{
            //方式一：getMapper
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();

            //方式二：
            //List<User> userList = sqlSession.selectList("com.rui.dao.UserDao.getUserList");

            for (User user : userList) {
                System.out.println(user);
            }

        }
        finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }

}

注意，当增删改需要提交事务

sqlSession.commit();

使用注解：

在dao目录下不用再创建*Mapper.xml，直接在*Mapper.java 接口中写入查询语句，例如：

@Select(value = "select * from user")
List<User> getUsers();

并且在核心配置文件mybatis-config.xml中绑定接口：

<!--绑定接口-->
<mappers>
    <mapper class="com.dong.dao.UserMapper"/>
</mappers>

这里跟使用xml绑定接口稍微不同。此处是使用class并用'.'来分割，而在xml绑定接口是使用resource并用‘/’来分割。