mybatis入门案例

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.po.domain"/>
    </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://127.0.0.1:3306/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://127.0.0.1:3306/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/po/mapper/UserMapper.xml"/>-->
        <!--Mapper代理方式-->
        <package name="com.po.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.po.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.po.domain;
 
 
// 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.po.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.po;
 
import com.po.domain.User;
import com.po.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;
import java.util.List;
 
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();*/
        //1. 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
        SqlSession sqlSession = sqlSessionFactory.openSession();
 
        //3. 获取Mapper接口的代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
 
        //4. 执行方法
        List<User> user = userMapper.selectAll();
        System.out.println(user);
 
        //5. 释放资源
        sqlSession.close();
 
    }
}

[User{id=1, username='zhangsan', password='123', gender='null', addr='null'}]

入门案例注意事项
环境搭建的注意事项
1持久层的操作接口名称和映射文件位置必须和mapper接口的包结构相同
2创建UserMapper.xml 和UserMapper.java时名称需要保持一致
说明
当核心配置文件mapper标签下以resource形式指向依赖配置文件时

<mapper resource="com/po/mapper/UserMapper.xml"/>
不需要保持一致
这样可以加载到其相应的依赖配置文件通过namespace找到其相应的方法
当mapper标签下以package包扫描形式时，需要保持一致。

<package name="com.po.mapper"/>
因为包扫描形式时实体类+Mapper接口通过动态代理调用方法而调用方法时会找其相应的映射配置文件当多个mapper接口和mapper.xml同时存在如果没有相同的名称，则动态代理就不能通过其一一对应的依赖配置文件创建其相应的实现方法
问题那namespace还有什么作用
3映射配置文件的mapper标签的namespace属性的取值必须是mapper接口的全限定类名
4映射配置文件的操作配置select等这些标签 id属性的取值必须是mapper接口的方法名
当我们遵从了上述几点之后我们在开发中就无须再写mapper的实现类