一、项目的目录结构：

二、回顾Mybatis的项目搭建步骤

1、导入相关的包(11个jar包) ¹
2、在src目录下编写编写配置文件（mybatis-cfg.xml）
3、编写实体类(User.java)
4、编写映射文件（UserMapper.xml）
5、编写测试文件
6、调用JUnit 5进行调试

相关jar包截图

mybatis-cfg.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="dev">
          <environment id="dev">
              <transactionManager type="JDBC" />
                  <dataSource type="POOLED">
                  
                  <property name="driver" value="com.mysql.jdbc.Driver"/>
                 <property name="url" value="jdbc:mysql://localhost:3306/java505"/>
                 <property name="username" value="root"/>
                 <property name="password" value="szxy"/>
                  </dataSource>
          </environment>
          
      </environments>
      <mappers>
         <mapper resource="cn/bjsxt/mapper/usermapper.xml"/>
      </mappers>
  </configuration>

注：java505为mysql下的数据库名。驱动器driver的值不能更改。

实体类：

设置私有变量，
实现序列化，
带参无参构造函数，
取值赋值方法，
改写toString方法，
hashCode（）和equals（）方法。

 import java.io.Serializable;
    
    public class User implements Serializable{
        private int id;
        private String name;
        private String password;
        
        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 getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        public User(int id, String name, String password) {
            super();
            this.id = id;
            this.name = name;
            this.password = password;
        }
        public User() {
            super();
        }
        @Override
        public String toString() {
            return "User [id=" + id + ", name=" + name + ", password=" + password + "]";
        }
        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + id;
            result = prime * result + ((name == null) ? 0 : name.hashCode());
            result = prime * result + ((password == null) ? 0 : password.hashCode());
            return result;
        }
        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            User other = (User) obj;
            if (id != other.id)
                return false;
            if (name == null) {
                if (other.name != null)
                    return false;
            } else if (!name.equals(other.name))
                return false;
            if (password == null) {
                if (other.password != null)
                    return false;
            } else if (!password.equals(other.password))
                return false;
            return true;
        }
        
        
    }

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 namespace="cn.bjsxt.mapper.UserMapper">
        <select id="selAll" resultType="cn.bjsxt.pojo.User">
            select * from t_user
        </select>      
        <select id="selOne" resultType="cn.bjsxt.pojo.User">
            select * from t_user where id=1
        </select>  
      </mapper>

*select id="selAll": 定义查询方法的名称
select from t_user：SQL语句为具体操作的内容

测试类testSelect.java

package cn.bjsxt.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;
import java.util.Set;

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 cn.bjsxt.pojo.User;

public class TestSelect {
    @Test
    public void testSelectList() throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-cfg.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = factory.openSession();
        //1、selectList
        /**List<User> list = session.selectList("cn.bjsxt.mapper.UserMapper.selAll");
        for (User user : list) {
            System.out.println(user);
        }*/
        //2、selectOne
        /**User user = session.selectOne("cn.bjsxt.mapper.UserMapper.selOne");
        System.out.println(user);*/
        //3、selectMap
        Map<Integer, User> map = session.selectMap("cn.bjsxt.mapper.UserMapper.selAll", "id");
        System.out.println(map);
        Set<Integer> set = map.keySet();
        for (Integer k : set) {
            System.out.println(map.get(k));
        }
        
        session.close();
    }
}

注：1、使用Junit 5需要在类里面添加一段代码@Test，并导入import org.junit.Test;

    2、selectAll查询的是所有对象，selectOne查询的是一个对象并且需要设置条件，selectMap查询的是具有键值关系的对象
    

提取码：gl59
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