搭建环境

搭建数据库

CREATE DATABASE mybatis;

USE mybatis;

CREATE TABLE `user`(
    `id` INT AUTO_INCREMENT NOT NULL,
    `name` VARCHAR(20),
    `pwd` VARCHAR(50),
    PRIMARY KEY(id)
)ENGINE=INNODB DEFAULT CHARSET=utf8;

新建项目

• 使用idea创建一个普通的maven项目

• 导入依赖

  <dependencies>
      <!--    sql依赖-->
      <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>5.1.47</version>
      </dependency>
      <!--    mybatis依赖-->
      <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.5.2</version>
      </dependency>
      <!--    junit依赖-->
      <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version> 4.13</version>
      </dependency>
  </dependencies>
  

创建一个模块

编写核心配置文件

在resource目录下创建 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?useSSL=false&amp;useUnicode=true&amp;characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

普通的maven项目访问不了src目录下的resources文件

需要在pom.xml里加上

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.xml</include>
            </includes>
        </resource>
    </resources>
</build>

编写mybatis util工具类

这里的工具类帮我们连接了数据库,SqlSession对象类似于Connection对象

package com.qin;

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 utils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        //获取sqlSessionFactory对象
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //使用SqlSessionFactory sqlSessionFactory创建sqlSession实例
    //SqlSession完全包含了面向数据库执行sql命令所需要的所有方法
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

编写代码

• 编写UserDao

  package com.qin.dao;
  
  import com.qin.pojo.User;
  
  import java.util.List;
  
  public interface UserDao {
      List<User> getUserList();
  }
  

• 编写Mapper.xml文件–>类似编写UserDaoImpl

  <?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">
  <!--类似继承UserDao接口-->
  <mapper namespace="com.qin.dao.UserDao">
  <!--    实现UserDao里面的方法-->
      <select id="getUserList" resultType="com.qin.pojo.User">
      select * from mybatis.user;
    </select>
  </mapper>
  

• 在mabatis-config.xml中注册 mapper

  <?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?useSSL=false&amp;useUnicode=true&amp;characterEncoding=utf-8"/>
                  <property name="username" value="root"/>
                  <property name="password" value="123456"/>
              </dataSource>
          </environment>
      </environments>
  <!--    注册mapper-->
      <mappers>
          <mapper resource="com/qin/dao/UserMapper.xml"/>
      </mappers>
  </configuration>
  

• 出现这个错误既是没有注册mapper

测试

package com.qin.dao;

import com.qin.pojo.User;
import com.qin.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test1(){
        //使用工具类获得SqlSesison
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

解决idea自动降低jdk版本

在 pom 文件中添加 maven-compiler-plugin 插件，并指定 jdk 使用的 jdk 版本即可解决上面问题。maven-compiler-plugin 的配置同时对 Java compiler 和 Language level 同时生效。

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
    </plugins>
</build>