Concept:

• mybatis is a persistence framework, a top-level project under apache
• Let the program focus on sql, through the mapping method provided by mybatis, free and flexible generation of SQL statements needed.
• The parameters in the prepareStatement can be automatically input mapped, and the query result set can be flexibly mapped to java objects. (output mapping)

Problems encountered:

①Loading class com.mysql.jdbc.Driver'. This is deprecated. The new driver class iscom.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

Cause: The latest mysql-connector-java-8.0.11-.jar MySQL driver package is used. The `com.mysql.jdbc.Driver'class in the new driver package is outdated. It is automatically registered through SPI and no longer needs to load the driver class manually.

②java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone.

Modification: value="jdbc: mysql://localhost:3306/test?serverTimezone=GMT%2B8"/

(3) When the content in the data table is of Date type, the query statement will report an error. I don't know why. If the big man knows, please tell him.

Architecture

2.png

Import the required jar package:

1.png

Query data according to Id

• log4j.properties

log4j.rootLogger = DEBUG,Console
log4j.appender.Console = org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout = org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern = %d[%t]%-5p [%c] - %m%n

• User.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="test">
     <select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.Employee">//parameterType input type, resultType output result type
         select id,username,sex,address from users where id=#{id};//#{} is a placeholder
     </select>
</mapper>

• SqlMapConfig.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.cj.jdbc.Driver"/> 
 <property name="url" value="jdbc:mysql://localhost:3306/test?serverTimezone=GMT%2B8"/> 
 <property name="username" value="root"/> 
 <property name="password" value=""/> 
 </dataSource>
 </environment>
</environments> 
<mappers>
   <mapper resource="sqlmap/User.xml"/>
</mappers>
</configuration>

• Employee.java

package cn.itcast.mybatis.po;
import java.sql.Date;
public class Employee {
    private int id;
    private String username;
    private String sex;
    private String address;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "Employee [id=" + id + ", username=" + username + ", sex=" + sex + ", address=" + address + "]";
    }
}

• MybatisFirst.java

package sqlmap;
import java.io.IOException;
import java.io.InputStream;
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.itcast.mybatis.po.Employee;
public class MybatisFirst { 
    @Test
    public void findUserByIdTest() throws IOException{
        String resource="SqlMapConfig.xml";//configuration file
         InputStream inputStream= Resources.getResourceAsStream(resource);//Get the configuration file stream
        SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);//Create a session factory and pass in configuration file information
        SqlSession sqlSession =sqlSessionFactory.openSession();//Get sqlsession from the factory
        Employee employee =sqlSession.selectOne("test.findUserById",1);//It's selectOne that queries a piece of data
        System.out.println(employee);
        sqlSession.close();  //Closing session
        }       
    }

Fuzzy query data by name

• SqlMapConfig.xml

 <select id="findUserByName" parameterType="java.lang.String" resultType="cn.itcast.mybatis.po.Employee">
         select id,username,sex,address from users where username like '%${value}%';//${} may cause sql injection, just a splice, without any change
 </select>

• Test file

@Test
    public void findUserByNameTest() throws IOException{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession =sqlSessionFactory.openSession();
        java.util.List<Employee> list= sqlSession.selectList("test.findUserByName", "zhao");//selectList Queries Multiple Data
        System.out.println(list);
               sqlSession.close();
        }       

Adding data to the database

• SqlMapConfig.xml

<insert id="insertUser" parameterType="cn.itcast.mybatis.po.Employee">
       <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
           select LAST_INSERT_ID(); //Query Self-Increasing Primary Key Value
       </selectKey>
     insert into users(id,username,sex,address)value(#{id},#{username},#{sex},#{address});
</insert>

• Test file

@Test
    public void insertUserTest() throws IOException{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession =sqlSessionFactory.openSession();
        Employee employee= new Employee();
        employee.setId(10);
        employee.setUsername("wu");
        employee.setSex("nv");
        employee.setAddress("henan");
        sqlSession.insert("test.insertUser",employee);
        sqlSession.commit();
               System.out.println(employee.getId());//Output Self-Increasing Primary Key Value
        sqlSession.close();
        }       

Delete files from the database

• SqlMapConfig.xml

<delete id="deleteUser" parameterType="java.lang.Integer">
         delete from users where id=#{id};
</delete>

• Test file

@Test
    public void deleteUserTest() throws IOException{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession =sqlSessionFactory.openSession();
        sqlSession.delete("test.deleteUser",12);
        sqlSession.commit();
        sqlSession.close();
        }

Update the data in the database

• SqlMapConfig.xml

<update id="updateUser" parameterType="cn.itcast.mybatis.po.Employee">
         update users set username=#{username},sex=#{sex},address=#{address} where id=#{id};   
</update>

• Test file

@Test
    public void updateUserTest() throws IOException{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource)；
        SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession =sqlSessionFactory.openSession();
        Employee employee= new Employee();
        employee.setId(13);
        employee.setUsername("sheng");
        employee.setSex("nv");
        employee.setAddress("diqiu");
        sqlSession.update("test.updateUser",employee);
        sqlSession.commit();
        sqlSession.close();
        }