MyBatis~(壹)初探.

项目代码
参照
简介
Hello-MyBatis
开始 CRUD
通过 Map 优化

项目代码

借物表

在此文章记录了: 😍Weidows-の成长路线#mybatis

简介

MyBatis 是优秀的持久层框架,简单来说就是方便存-取数据的工具.

持久层: Dao 层、Service 层、Controller 层

之前听说过 MyBatis-plus,这里贴一篇二者的区别
MyBatis 与 MyBatis-plus 的区别
下图中蓝色小鸟就是 MyBatis-plus

Hello-MyBatis

环境配置

用 Maven 创建空项目,导入依赖&设置 Maven 过滤器:

<!--导入依赖-->
<dependencies>
  <!--mysqlq驱动-->
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.12</version>
  </dependency>
  <!--mybatis-->
  <dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.4</version>
  </dependency>
  <!--junit-->
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
  </dependency>
  <dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.20</version>
  </dependency>
</dependencies>

<!--Mapper资源导出,不设置的话会报错-->
<build>
  <resources>
    <resource>
      <directory>src/main/resources</directory>
      <includes>
        <include>**/*.properties</include>
        <include>**/*.xml</include>
      </includes>
      <filtering>true</filtering>
    </resource>
    <resource>
      <directory>src/main/java</directory>
      <includes>
        <include>**/*.properties</include>
        <include>**/*.xml</include>
      </includes>
      <filtering>true</filtering>
    </resource>
  </resources>
</build>

然后创建空的子模块,子模块中开发就不需要再导入依赖了,MyBatis 需要添加一个配置文件: src/main/resources/MyBatis-config.xml

后面每增加一个 Mapper.xml,都需要在这里面添加 Mapper 映射;后面会提到.

<?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核心配置文件-->
<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?userSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

数据库

初始化数据库和 pojo

create schema User;


create table User
(
  id   int                      not null,
  name varchar(30) default null null,
  pwd  varchar(30) default null null,
  constraint User_pk
    primary key (id)
) ENGINE = INNODB
  DEFAULT CHARACTER SET = utf8;


insert into User(id, name, pwd)
values (1, '张三', 123456),
      (2, '李四', 123456),
      (3, '王五', 123456),
      (4, '赵六', 123456)

src/main/java/pojo/User.java

package pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
  private int id;
  private String name;
  private String pwd;
}

工具类

src/main/java/utils/MyBatisUtils.java

package utils;

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;

//sqlSessionFactory --> sqlSession
public class MyBatisUtils {
  private static SqlSessionFactory sqlSessionFactory = null;

  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();
    }
  }

  /**
  * 既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例.
  * SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
  */
  public static SqlSession getSqlSession(){
    return sqlSessionFactory.openSession();
  }
}

Dao

dao 中编写接口和绑定 Mapper.xml

https://github.com/Weidows/Java/blob/master/MyBatis/1-hello-MyBatis/src/main/java/dao

这里的 xml 配置绑定好接口,就可以让 MyBatis 负责 SQL 代码了,避免了 dao 层中 JDBC 代码过于繁杂和重复的问题

<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<!--namespace=绑定一个指定的Dao/Mapper接口-->
<mapper namespace="dao.UserMapper">
  <!--这里id就是方法名,相当于实现方法-->
  <select id="getUserList" resultType="pojo.User">
    select *
    from User
  </select>
</mapper>

Mapper.xml 绑定的是与之对应的接口,然后需要在 MyBatis-config.xml中绑定需要的 Mapper.xml

绑定关系: UserMapper.java -> UserMapper.xml -> MyBatis-config.xml

添加绑定如下:

<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE configuration
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<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?userSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
  </environments>

  <!--绑定Mapper.xml-->
  <mappers>
    <mapper resource="dao/UserMapper.xml"/>
  </mappers>
</configuration>

测试

注意 test 中层级与 main 中层级一一对应

package dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.MyBatisUtils;

import java.util.List;

public class UserMapperTest {
  @Test
  public void test() {
    //1.获取SqlSession对象
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    //2.执行SQL
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = userMapper.getUserList();
    for (User user : userList) {
      System.out.println(user);
    }
    //关闭sqlSession
    sqlSession.close();
  }

  @Test
  public void test1() {
    //1.获取SqlSession对象
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    //2.执行SQL
    List<User> userList = sqlSession.selectList("dao.UserMapper.getUserList");
    for (User user : userList) {
      System.out.println(user);
    }
    //关闭sqlSession
    sqlSession.close();
  }
}

排错:
- org.apache.ibatis.binding.BindingException: Type interface dao.UserDao is not known to the MapperRegistry.
  这是因为 Mapper.xml 资源没有被 Maven 导出,所以找不到资源,解决办法:资源导出
- 1字节的UTF-8序列的字节1无效的问题处理
  这个问题格外 dan 疼,把下面的 UTF-8 改为 UTF8 试试…
  <?xml version="1.0" encoding="UTF-8" ?>

开始 CRUD

完善 CRUD 只需要修改下面三个文件:

src/main/java/dao/UserMapper.java

package dao;

import pojo.User;

import java.util.List;

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

  User getUserById(int id);

  int addUser(User user);

  int updateUser(User user);

  int deleteUser(int id);
}

src/main/java/dao/UserMapper.xml

<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<!--namespace=绑定一个指定的Dao/Mapper接口-->
<mapper namespace="dao.UserMapper">
  <!--这里id就是方法名,相当于实现方法-->
  <select id="getUserList" resultType="pojo.User">
    select *
    from User
  </select>

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

  <insert id="addUser" parameterType="pojo.User">
    insert into mybatis.user(id, name, pwd)
    values (#{id}, #{name}, #{pwd})
    ## 对象中的属性可以被直接取出来(这里取得可以是传入的参数,也可以是传入对象的属性)
  </insert>

  <update id="updateUser" parameterType="pojo.User">
    update mybatis.user
    set name =#{name},
        pwd=#{pwd}
    where id = #{id}
  </update>

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

src/test/java/dao/UserMapperTest.java

package dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.MyBatisUtils;

import java.util.List;

public class UserMapperTest {
  @Test
  public void test() {
    //1.获取SqlSession对象
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    //2.执行SQL
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = userMapper.getUserList();
    for (User user : userList) {
      System.out.println(user);
    }
    //关闭sqlSession
    sqlSession.close();
  }

  @Test
  public void test1() {
    //1.获取SqlSession对象
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    //2.执行SQL
    List<User> userList = sqlSession.selectList("dao.UserMapper.getUserList");
    for (User user : userList) {
      System.out.println(user);
    }
    //关闭sqlSession
    sqlSession.close();
  }

  @Test
  public void getUserById() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    System.out.println(mapper.getUserById(3));
    sqlSession.close();
  }

  @Test
  public void addUser() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int i = mapper.addUser(new User(5, "五号", "123456"));
    if (i > 0) {
      //注意 增删改 需要提交事务
      sqlSession.commit();
    }
    sqlSession.close();
  }

  @Test
  public void updateUser() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int i = mapper.updateUser(new User(5, "⑤号", "654321"));
    if (i > 0) {
      sqlSession.commit();
    }
    sqlSession.close();
  }

  @Test
  public void deleteUser() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int i = mapper.deleteUser(5);
    if (i > 0) {
      sqlSession.commit();
    }
    sqlSession.close();
  }

}

通过 Map 优化

//用Map插入用户
int addUser2(Map<String, Object> map);

<!--通过USer传参的话,必须用User的属性名取出; 而通过map传参的话,属性名可以任意-->
<insert id="addUser2" parameterType="Map">
  insert into mybatis.user(id, name, pwd)
  values (#{userid}, #{username}, #{userpassword})
</insert>

@Test
public void addUser2() {
  SqlSession sqlSession = MyBatisUtils.getSqlSession();
  UserMapper mapper = sqlSession.getMapper(UserMapper.class);

  HashMap<String, Object> map = new HashMap<>();
  map.put("userid", 6);
  map.put("username", "王虎");
  map.put("userpassword", 789);

  int i = mapper.addUser2(map);
  if (i > 0) sqlSession.commit();
  sqlSession.close();
}