2021-03-03

idea20.1.1创建maven工程搭建mybatis
注意
在idea2020.1.1版与前面有细小差异


在idea2020.1.1出现变化

开始搭建mybatis
引入驱动包

<dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.3.0</version>
      </dependency>
         <!-- mysql驱动包 -->
          <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.29</version>
            </dependency>
         <!-- junit测试包 -->
          <dependency>
               <groupId>junit</groupId>
               <artifactId>junit</artifactId>
               <version>4.11</version>
                <scope>test</scope>
          </dependency>

idea20.1.1后会自己更改Java 与resources

手动添加

在resources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>
    <!-- 环境配置 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!-- 数据库连接相关配置 ,这里动态获取config.properties文件中的内容-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
                <property name="username" value="root" />
                <property name="password" value="**" />
            </dataSource>
        </environment>
    </environments>
    <!-- mapping文件路径配置 -->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

</configuration>

在resources下创建mapper包 接着创建UserMapper.xml

<?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">
<!-- mapper为映射的根节点，namespace指定Dao接口的完整类名    mybatis会依据这个接口动态创建一个实现类去实现这个接口，    而这个实现类是一个Mapper对象-->
<mapper namespace="com.ljt.dao.UserMapper">
    <select id="findById" parameterType="int" resultType="com.ljt.pojo.User">
      select * from users where uid = #{id}
    </select>
</mapper>

在Java里面创建com.pojo与dao包
pojo里面是

package com.ljt.pojo;
public class User {
    private int uid;
    private String uname;
    private int uage;

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getUname() {
        return uname;
    }

    public void setUname(String uname) {
        this.uname = uname;
    }

    public int getUage() {
        return uage;
    }

    public void setUage(int uage) {
        this.uage = uage;
    }
}

在dao里面是一个接口

```java
package com.ljt.dao;

import com.ljt.pojo.User;

import java.util.List;

public interface UserMapper {
    public List<User> findById(int  id);
}

测试类

```java

import com.ljt.dao.UserMapper;
import com.ljt.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 org.junit.Test;

import java.io.IOException;
import java.io.Reader;
import java.sql.ClientInfoStatus;
import java.util.List;

public class UserTest {
    @Test
    public void userFindByIdTest(){
        //定义读取文件名
        String resources = "mybatis-config.xml";
        //创建流
        Reader reader=null;
        try {
            //读取mybatis-config.xml文件到reader对象中
            reader= Resources.getResourceAsReader(resources);
        } catch (IOException e) {
            e.printStackTrace();
        }
        //初始化mybatis,创建SqlSessionFactory类的实例
        SqlSessionFactory sqlMapper=new SqlSessionFactoryBuilder().build(reader);
        //创建session实例
        SqlSession session=sqlMapper.openSession();
        //传入参数查询，返回结果
        UserMapper userMapper=session.getMapper(UserMapper.class);
        List<User> user=userMapper.findById(1);
        //输出结果
        System.out.println(user);
        //关闭session
        session.close();

    }
}