• Mybatis入门

一、Mybatis简介

1.1、简介

• Mybatis是一款优秀的持久层框架
• 支持自定义SQL、存储过程和高级映射。几乎免除了所有的JDBC代码和处理结果集代码。通过简单地XML或注解来配置。

1.2、持久化

数据持久化

• 持久化就是将程序的数据在持久状态和瞬时状态转化的过程
• 内存：断电即失
• 数据库（JDBC）、io持久化

为什么要持久化？

• 有一些对象，不能丢掉
• 内存太贵

1.3、持久层

Dao层、Service层、Controller层

• 完成持久化工作的代码
• 层界限十分明显

1.4、为什么使用Mybatis

• 帮助程序员将数据放到数据库中

• 方便

• 传统的JDBC代码太复杂，简化，框架，自动化

• 不用Mybatis也可以，用了更方便

• 优点：

  • 简单易学
  • 灵活
  • sql与代码分离，提高了可维护性
  • 提供映射标签，支持对象与数据库的orm字段关系映射
  • 提供对象关系映射标签，支持对象关系组建维护
  • 提供xml标签，支持编写动态sql

二、编写第一个Mybatis

2.1、搭建环境

1. 创建一个普通的maven项目（作为父工程）

2. 删除src目录，new Module作为子工程

3. 导入依赖（mybatis、mysql、junit）

   <dependencies>
           <!--mybatis驱动-->
           <dependency>
               <groupId>org.mybatis</groupId>
               <artifactId>mybatis</artifactId>
               <version>3.4.6</version>
           </dependency>
   ?
           <!-- mysql驱动 -->
           <dependency>
               <groupId>mysql</groupId>
               <artifactId>mysql-connector-java</artifactId>
               <version>8.0.23</version>
           </dependency>
   ?
           <!--junit驱动-->
           <dependency>
               <groupId>junit</groupId>
               <artifactId>junit</artifactId>
               <version>4.12</version>
               <scope>test</scope>
           </dependency>
   ?
       </dependencies>
    

    

2.2、创建new Module

• 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>
      <environments default="development">
          <environment id="development">
              <transactionManager type="JDBC"/>
              <dataSource type="POOLED">
                  <property name="driver" value="com.mysql.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>
  ?
  <mappers>
      <mapper resource="com/aishimin/dao/UserMapper.xml"/>
  </mappers>
  </configuration>

   

• 编写mybatis工具类获取SqlSession

  package com.aishimin.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;
  ?
  public class MybatisUtils {
     
      static SqlSessionFactory sqlSessionFactory = null;
  ?
      static{
          //使用mybatis步骤
          //1、获取SqlSession
          String resource = "mybatis-config.xml";
          InputStream inputStream = null;
          try {
              inputStream = Resources.getResourceAsStream(resource);
              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
      //既然有了sqlSessionFactory实例，我们通过openSession可以获取SqlSession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();
      }
  ?
  }
   

   

2.3、编写代码

• 编写实体类User

package com.aishimin.entity;
?
public class User {
    private int id;
    private String name;
    private String pwd;
?
    public User(){};
?
    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }
?
    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 String getPwd() {
        return pwd;
    }
?
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
?
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name=‘" + name + ‘\‘‘ +
                ", pwd=‘" + pwd + ‘\‘‘ +
                ‘}‘;
    }
}
 

• 编写UserMapper接口（实际上就是MVC中的UserDao）

  package com.aishimin.dao;
  ?
  import com.aishimin.entity.User;
  ?
  import java.util.List;
  ?
  public interface UserMapper {
      //查询所有用户，返回值为User结果集合
      List<User> getUserList();
  ?
      //通过id查找用户
      User getUserById(int id);
  ?
      //增加用户
      int addUser(User user);
  ?
      //更新用户
      int updateUser(User user);
  ?
      //通过Id删除用户
      int deleteUserById(int id);
  
      //模糊查询
      List<User> getUserLike(Map<String,Object> map);
  ?
  }

   

   

• 编写UseMapper.xml其作用相当于UserMapper的实现类

  <?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必须域类名对应一致
  <mapper namespace="com.aishimin.dao.UserMapper">
  ?
      //id为方法名
      //resultType为结果返回类型
      //parameterType为参数类型
      <select id="getUserList" resultType="com.aishimin.entity.User">
          select *from mybatis.user;
      </select>
  ?
      <select id="getUserById" parameterType="int" resultType="com.aishimin.entity.User">
          select *from mybatis.user where id = #{id}
      </select>
  ?
      <insert id="addUser" parameterType="com.aishimin.entity.User">
          insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
      </insert>
  ?
      <update id="updateUser" parameterType="com.aishimin.entity.User">
          update mybatis.user set name = #{name},pwd = #{pwd} where id = #{id};
      </update>
  ?
      <delete id="deleteUserById" parameterType="int">
          delete from user where id = #{id};
      </delete>
          
      <select id="getUserLike" resultType="com.aishimin.entity.User" parameterType="map">
          select *from mybatis.user where name like #{userid}
   
   
      </select>
      
  </mapper>

   

• 编写测试类

  package com.aishimin.dao;
  ?
  import com.aishimin.entity.User;
  import com.aishimin.utils.MybatisUtils;
  import org.apache.ibatis.session.SqlSession;
  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 user:userList){
              System.out.println(user);
          }
  ?
          sqlSession.close();
      }
      @Test
      public void testQuery(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
  ?
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
  ?
          User user = mapper.getUserById(1);
          System.out.println(user);
          sqlSession.close();
  ?
      }
  ?
      
      //增删改需要提交事务，否则数据库信息无法更新
      @Test
      public void testInsert(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
  ?
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
          User user = new User(3,"娜美","123456789");
  ?
          int res = mapper.addUser(user);
          if(res>0){
              System.out.println("插入成功");
          }
          sqlSession.commit();
          sqlSession.close();
      }
  ?
      @Test
      public void testUpdate(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
  ?
          int res = mapper.updateUser(new User(3,"乔巴","789456123"));
          if(res>0){
              System.out.println("修改成功");
          }
  ?
          sqlSession.commit();
          sqlSession.close();
      }
  ?
      @Test
      public void testDelete(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
  ?
          int res = mapper.deleteUserById(3);
  ?
          if(res>0){
              System.out.println("删除成功");
          }
          sqlSession.commit();
          sqlSession.close();
  ?
  ?
      }
      
      //模糊查询
       @Test
      public void testgetUserList(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
  ?
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
  ?
          Map<String,Object> map = new HashMap<>();
          map.put("userid","%路%");
          List<User> users = mapper.getUserLike(map);
          for (User user:users){
              System.out.println(user);
          }
          sqlSession.close();
      }
      
      
  }

   

   

  这里会遇到两个常见的错误，需要注意！

  第一个错误：org.apache.ibatis.binding.BindingException: Type interface com.aishimin.dao.UserMapper is not known to the MapperRegistry.

  遇到这个错误的原因是因为mybatis核心配置中没有注册mappers

  需要在mybatis-config.xml中加入：

  <mappers>
      <mapper resource="com/aishimin/dao/UserMapper.xml"/>
  </mappers>
   

   

  第二个错误：

  遇到这个错误的原因是因为程序无法检测到我们编写的UserMapper.xml，需要在pom.xml中加入如下配置：

   

  <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>

   

   

  万能Mapper测试

  这种方法属于野路子，适合于针对sql语句中参数较多的情况：

   

  User getUserById2(Map<String,Object> map);

   

  <select id="getUserById2" resultType="com.aishimin.entity.User" parameterType="map">
      select *from mybatis.user where id = #{userid}
  </select>

   

  @Test
  public void testQuery2(){
      SqlSession sqlSession = MybatisUtils.getSqlSession();
  ?
      UserMapper mapper = sqlSession.getMapper(UserMapper.class);
  ?
      Map<String,Object> map = new HashMap<>();
      
      //Mapper传递参数只需要取出key即可
      map.put("userid",2);
      User user = mapper.getUserById2(map);
  ?
      System.out.println(user);
      sqlSession.close();
  ?
  }
   

   

   

   

原文：https://www.cnblogs.com/aishimin/p/14418485.html