MyBits

1.1 Mybits安装

Maven

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.6</version>
</dependency>

1.2 Mybits使用

1.2.1 配置Mybits连接数据库配置

相当于JDBC创建连接

<?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.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="131865"/>
            </dataSource>
        </environment>

<!--        <environment id="development2">-->
<!--            <transactionManager type="JDBC"/>-->
<!--            <dataSource type="POOLED">-->
<!--                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>-->
<!--                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;serverTimezone=UTC"/>-->
<!--                <property name="username" value="root"/>-->
<!--                <property name="password" value="131865"/>-->
<!--            </dataSource>-->
<!--        </environment>-->
        
        
<!--        <environment id="">-->
<!--            ....-->
<!--        </environment>-->
        
    </environments>
    
    
    
    <mappers>
        <mapper resource="org/example/DAO/UserMapper.xml"/>
    </mappers>
    
</configuration>

1.2.2 创建SQLSessionFactory

工厂用于获取SqlSession

package org.example.MybatisUtils;

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=null;
    static {

        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

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

1.2.3 用户类

package org.example.mybatisDO;

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

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

    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;
    }
}

1.2.4 UserMapper 接口

package org.example.DAO;

import org.example.mybatisDO.User;

import java.util.List;

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

    User getUserById(int 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="org.example.DAO.UserMapper">

    <select id="getUserList" resultType="org.example.mybatisDO.User" >
        select * from user;
    </select>

    <select id="getUserById" resultType="org.example.mybatisDO.User" parameterType="int">
        select * from user where id=#{id};
    </select>
</mapper>

1.2.5 测试

package org.example.DAO;

import org.apache.ibatis.session.SqlSession;
import org.example.MybatisUtils.MybatisUtils;
import org.example.mybatisDO.User;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {
    @Test
    public void test(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();

        for (User u:userList){
            System.out.println(u.toString());
        }
        sqlSession.close();
    }
    @Test
    public void testGetUserById(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user.toString());
        sqlSession.close();
    }
}

1.3 常见问题

1、Type interface org.example.DAO.UserMapper is not known to the MapperRegistry.

在主配置mybatis-config.xml中没有注册Mapper

应在mybatis-config.xml中加入

    <mappers>
        <mapper resource="org/example/DAO/UserMapper.xml"/>
    </mappers>

2、Maven因添加文件过滤，否则可能导致不符合约定的文件无法输出

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
</build>