How to write configuration files and use MyBatis simply

<?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> 
  <typeAliases> 
    <!-- Alias ​​of configuration type --> 
    <typeAlias ​​alias="User" type="cn.hncu.domain.User" /> 
  </typeAliases> 
  <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://127.0.0.1:3306/mybatis?characterEncoding=UTF-8" /> 
        <property name="username" value="hncu" /> 
        <property name="password" value="1234" /> 
        <property name="poolMaximumActiveConnections" value="5"/> 
      </dataSource> 
    </environment> 
  </environments> 
  <mappers> 
    <mapper resource="cn/hncu/domain/User.xml"></mapper> 
    <mapper resource="cn/hncu/domain/User2.xml"></mapper> 
  </mappers> 
</configuration>

package cn.hncu.utils; 
 
import java.io.IOException; 
import java.io.InputStream; 
import java.sql.Connection; 
 
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 com.mysql.jdbc.interceptors.SessionAssociationInterceptor; 
 
 
public class SqlSessionUtils { 
  private static SqlSessionFactory sessionFactory=null;//DataSource--pool 
  static{ 
    try { 
      InputStream in=Resources.getResourceAsStream("mybatis-config.xml");//Load configuration file sessionFactory=new SqlSessionFactoryBuilder().build(in); 
      /* 
       * Here is a method that does not require the use of Resources class to load files (using ClassLoader to load configuration files at the bottom level) 
        sessionFactory = new SqlSessionFactoryBuilder().build(SqlSessionUtils.class.getClassLoader().getResourceAsStream("mybatis-config.xml")); 
       */ 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } 
  } 
   
  public static SqlSessionFactory getSessionFactory(){ 
    return sessionFactory; 
  } 
  public static SqlSession getSqlSession(){ 
    return sessionFactory.openSession(); 
  } 
  public static void main(String[] args) { 
    //Mybatis controls the number of connections in the pool for(int i=0;i<10;i++){ 
      SqlSession s=getSqlSession(); 
      System.out.println(s); 
      Connection con=s.getConnection(); 
      System.out.println("con: "+con); 
    } 
  } 
}

package cn.hncu.domain; 
 
public class User { 
  private String id; 
  private String name; 
  private String pwd; 
  public String getId() { 
    return id; 
  } 
  public void setId(String 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 + "]"; 
  } 
   
}

package cn.hncu.domain; 
 
import java.util.List; 
 
public interface UserMapper { 
  public List<User> all(); 
  public List<User> user2(String string); 
  public List<User> user3(User user); 
}

package cn.hncu.domain; 
 
import java.util.List; 
 
public interface UserMapper { 
  public List<User> all(); 
  public List<User> user2(String string); 
  public List<User> user3(User user); 
}

package cn.hncu.demo; 
 
import java.util.HashMap; 
import java.util.List; 
import java.util.Map; 
 
import org.apache.ibatis.session.SqlSession; 
import org.junit.Test; 
 
import cn.hncu.domain.User; 
import cn.hncu.domain.UserMapper; 
import cn.hncu.utils.SqlSessionUtils; 
 
public class Demo1 { 
  @Test 
  public void test1(){ 
    //Get SqlSession first 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
    List<User> list=s.selectList("users.all");//The returned result is encapsulated in list, and the parameter uses id to specify which section in the mapping file to use, <select> or <insert> and other sql operations// List<User> list=s.selectList("all");//Omit the namespace----If the name (id) conflicts, the namespace must be used for identification//System.out.println(list); 
    for(User u:list){ 
      System.out.println(u); 
    } 
  } 
  <span style="color:#ff0000;">//Use the interface method to operate the database (this method is recommended and safer) 
  /*Steps* 1. Write an interface: UserMapper. The abstract method name in the interface must be the same as the attribute id value of <select>, that is, an abstract method represents an operation.* 2. Change the namespace in User2.xml to the full class name of the interface.* 3. In the test code (java at the dao layer), use "s.getMapper()" to get a proxy class object, and use the object to call a method, that is, to perform a certain operation.*/</span> 
   
  @Test//Interface-oriented approach, the following calls are: User2.xml 
  public void test2(){ 
    //Get SqlSession first 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
    UserMapper m=s.getMapper(UserMapper.class);//Get a proxy object List<User>list=m.all(); 
    System.out.println(list); 
  } 
  ///////////////test3()demonstrates the single condition query in the conditional query, calling User2.xml/////////////////// 
   
  @Test//Traditional method public void test3_1(){ 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
// List<User> users=s.selectList("cn.hncu.domain.UserMapper.all"); 
    List<User> users=s.selectList("user2","2"); //The returned result is encapsulated in List, and the internal element file type is configured by the mapping file System.out.println(users); 
  } 
  @Test//Interface-oriented approach public void test3_2(){ 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
    UserMapper u=s.getMapper(UserMapper.class); 
    List<User> users=u.user2("3"); 
    System.out.println(users); 
  } 
   
  ///////////////////Multiple condition query (it is best to use object encapsulation conditions for condition query)////////////// 
  @Test 
  public void test4(){ 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
     
    UserMapper u=s.getMapper(UserMapper.class); 
    User user=new User(); 
    user.setId("4"); 
    user.setName("Erdan"); 
    List<User> users=u.user3(user); 
    System.out.println(users); 
  } 
  @Test 
  public void test5(){//Return the result using map 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
    System.out.println(s); 
    List<Map<String,Object>> users=s.selectList("user4"); 
    for(Map<String,Object> user:users){ 
      System.out.println(user); 
    } 
  } 
  @Test//Set the input parameter to map 
  public void test6(){ 
    SqlSession s=SqlSessionUtils.getSqlSession(); 
    Map<String, Object> map=new HashMap<String,Object>(); 
    map.put("id", "5"); 
    map.put("name", "Xiaoqi"); 
    List<Map<String,Object>> users=s.selectList("user5",map); 
    for(Map<String,Object> user:users){ 
      System.out.println(user); 
    } 
  } 
}

<?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"> 
<!-- The current configuration file is dedicated to displaying the interface-oriented operation mode--> 
<!--  
<mapper namespace="cn.hncu.domain.UserMapper"> 
  <select id="all" resultType="cn.hncu.domain.User"> 
    select * from users 
  </select> 
</mapper> 
--> 
<mapper namespace="cn.hncu.domain.UserMapper"> 
<!-- Type alias used --> 
  <select id="all" resultType="User"> 
    select * from users 
  </select> 
   
  <!--Single condition query of conditional query, the parameters of the following sql statement can be written arbitrarily--> 
  <select id="user2" resultType="User" parameterType="string"> 
    select * from users where id=#{xx} 
  </select> 
  <!--Multiple conditional queries for conditional queries, the parameters of the following SQL statements must be consistent with the attribute names of the value object (use the if conditional statement to determine whether the parameter is empty) --> 
  <select id="user3" resultType="User" parameterType="string"> 
    select * from users where id=#{id} 
    <if test="name!=null"> 
      and name=#{name} 
    </if> 
  </select> 
  <!-- Encapsulate the query results into List<Map<>> --> 
  <select id="user4" resultType="map"> 
    select * from users 
  </select> 
  <!-- Encapsulate the input parameters into a map type --> 
  <select id="user5" resultType="hashmap" parameterType="hashmap"> 
    select * from users where id=#{id} 
    <if test="name!=null"> 
      and name=#{name} 
    </if> 
  </select> 
</mapper>