【Mybatis】（接口式）

前期准备：

一张表（！已经连接数据库！我的数据库叫book，表名为user，有id、name、age三列）

项目结构：（log4j可以没有）

1，创建一个空的Maven项目

然后在pom.xml中导入依赖（mybatis需要3个依赖，junit测试依赖包、mybatis依赖包、SQL连接依赖包）

<dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.25</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.14</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>

    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.12</version>
    </dependency>
</dependencies>

2.com包下创建3个包mapper（存放接口）、pojo（存放实体类）、utils（可以把创建工厂的前期过程放在这个包里面，目的是简化代码）

（1）pojo下创建User类

package com.pojo;

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

    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;
    }

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

（2）mapper下创建UserMapper接口

package com.mapper;

import com.pojo.User;

public interface UserMapper {
    public User findUserById(int id);
}

（3）utils下创建MyBatisUtils

package com.utils;

import com.mapper.UserMapper;
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 factory;
    static {
        try {
            InputStream in= Resources.getResourceAsStream("mybatis-config.xml");
            factory=new SqlSessionFactoryBuilder().build(in);
            SqlSession sqlSession=factory.openSession();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    public static SqlSession getSession(){
        return factory.openSession();
    }
}

3.在resource下创建数据库连接池db.properties

#mysql
db.username=root
db.password=123456
db.jdbcUrl=jdbc:mysql://127.0.0.1:3306/book?useSSL=false&characterEncoding=utf-8
db.driverClass=com.mysql.cj.jdbc.Driver

！！注意数据库密码和数据库名字

4.在resource的mapper目录下创建UserMapper.xml文件，里面存放SQL语句（如果没有mapper目录，就自己创建）!!!!名称空间一定要是接口的全路径且SQL语句id要的接口的方法名保持一致

<?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">
<!--名称空间，如果是接口开发，名称空间名一般为接口所在的全路径-->
<mapper namespace="com.mapper.UserMapper">
    <!--    结果集映射，一般用于select查询的结果映射-->
    <resultMap id="UserInfoMap" type="com.pojo.User">
        <id property="id" column="id"></id>
        <result property="name" column="name"></result>

    </resultMap>
    <parameterMap id="parameterMap" type="com.pojo.User">
        <parameter property="id" resultMap="id"></parameter>
        <parameter property="name" resultMap="name"></parameter>

    </parameterMap>
    <!--    sql语句 id是该语句的唯一标识-->
    <select id="findUserById" resultMap="UserInfoMap">
        select *
        from user
        where id = #{id}
    </select>
</mapper>

5.在resource下创建mybatis的核心配置文件mybatis-config.xml（log4j可有可无）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--加载属性文件db.properties-->
    <properties resource="db.properties"></properties>
    <!--<settings></settings>-->
    <settings>
        <!--        开启驼峰映射-->
        <setting name="mapUnderscoreToCamelCase" value="ture"/>
    </settings>
    <!--        扫描包，别名映射-->
    <typeAliases>
        <package name="com.pojo"/>
    </typeAliases>
    <!--环境配置-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${db.driverClass}"/>
                <property name="url" value="${db.jdbcUrl}"/>
                <property name="username" value="${db.username}"/>
                <property name="password" value="${db.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--    sql语句的xml映射-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

6.在test中的目录java下创建com.test的包，然后在里面创建一个Test的测试类（如果@org.junit.Test报错那把它改为@Test即可）

package com.test;

import com.mapper.UserMapper;
import com.pojo.User;
import com.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;


public class Test {


    @org.junit.Test
    public void findUserById(){
        SqlSession session= MybatisUtils.getSession();
        UserMapper userMapper=session.getMapper(UserMapper.class);
        User user=userMapper.findUserById(2);
        System.out.println(user);
        session.commit();
        session.close();
    }
}

最后运行