mybatis简化代码

创建模块，导入坐标：

 <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <!--mybatis 依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>

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

        <!--junit 单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>


        <!-- 添加slf4j日志api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.20</version>
        </dependency>
        <!-- 添加logback-classic依赖 -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        <!-- 添加logback-core依赖 -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.2.3</version>
        </dependency>

    </dependencies>

编写 MyBatis 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>

    <typeAliases>
        <package name="com.itheima.pojo"/>
    </typeAliases>
    
    <!--
    environments：配置数据库连接环境信息。可以配置多个environment，通过default属性切换不同的environment
    -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false&allowPublicKeyRetrieval=true"/>
                <property name="username" value="root"/>
                <property name="password" value="wang0516"/>
            </dataSource>
        </environment>

        <environment id="test">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false&allowPublicKeyRetrieval=true"/>
                <property name="username" value="root"/>
                <property name="password" value="wang0516"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--加载sql映射文件-->
       <!-- <mapper resource="com/itheima/mapper/UserMapper.xml"/>-->

        <!--Mapper代理方式-->
        <package name="com.itheima.mapper"/>

    </mappers>

</configuration>

编写 SQL 映射文件 

<?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">

<!--
    namespace:名称空间
-->

<mapper namespace="com.itheima.mapper.UserMapper">

    <!--statement-->
    <select id="selectAll" resultType="user">
        select *
        from tb_user;
    </select>
<!--    <select id="selectById" resultType="user">
        select *
        from tb_user where id = #{id};

    </select>-->


    <select id="select" resultType="user">
        select *
        from tb_user
        where
            username = #{username}
        and password = #{param2}
    </select>


</mapper>

定义POJO类

package com.itheima.pojo;


// alt + 鼠标左键 整列编辑
public class User {

    private Integer id;
    private String username;
    private String password;
    private String gender;
    private String addr;

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", gender='" + gender + '\'' +
                ", addr='" + addr + '\'' +
                '}';
    }
}

usermapper

package com.itheima.mapper;

import com.itheima.pojo.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;

public interface UserMapper {

    List<User> selectAll();

    @Select("select * from tb_user where id  = #{id}")
    User selectById(int id);

    /*

      MyBatis 参数封装：
        * 单个参数：
            1. POJO类型：直接使用，属性名 和 参数占位符名称 一致
            2. Map集合：直接使用，键名 和 参数占位符名称 一致
            3. Collection：封装为Map集合，可以使用@Param注解，替换Map集合中默认的arg键名
                map.put("arg0",collection集合);
                map.put("collection",collection集合);
            4. List：封装为Map集合，可以使用@Param注解，替换Map集合中默认的arg键名
                map.put("arg0",list集合);
                map.put("collection",list集合);
                map.put("list",list集合);
            5. Array：封装为Map集合，可以使用@Param注解，替换Map集合中默认的arg键名
                map.put("arg0",数组);
                map.put("array",数组);
            6. 其他类型：直接使用
        * 多个参数：封装为Map集合,可以使用@Param注解，替换Map集合中默认的arg键名
            map.put("arg0",参数值1)
            map.put("param1",参数值1)
            map.put("param2",参数值2)
            map.put("agr1",参数值2)
            ---------------@Param("username")
            map.put("username",参数值1)
            map.put("param1",参数值1)
            map.put("param2",参数值2)
            map.put("agr1",参数值2)

     */
    User select(@Param("username") String username,String password);
    User select(Collection collection);
}

加载核心配置文件，获取 SqlSessionFactory 对象

package com.itheima;


import com.itheima.pojo.User;
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;
import java.util.List;

/**
 * Mybatis 快速入门代码
 */
public class MyBatisDemo {

    public static void main(String[] args) throws IOException {

        //1. 加载mybatis的核心配置文件，获取 SqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //2. 获取SqlSession对象，用它来执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //3. 执行sql
        List<User> users = sqlSession.selectList("test.selectAll");
        System.out.println(users);
        //4. 释放资源
        sqlSession.close();

    }
}