详解Mybatis模板(已优化)适合小白

#创建一个mybatis数据库

create database `mybatis`;

#使用mybatis数据库

use `mybatis`;

#创建一个user表，有id、username、password三个字段

create table `user`(

   `id` int ( 10 ) not null primary key auto_increment,

   `username` varchar( 30 ) default null ,

   `password` varchar( 30 ) default null

)engine=InnoDB default charset=utf8;

#插入数据

insert into `user`（`username`,`password`） values

( '张三' ， 123456 )，

( '李四' ， 123456 )，

( '王五' ， 123456 )；

<dependencies>

     <dependency>

<!--mysql依赖包-->

       <groupId>mysql</groupId>

       <artifactId>mysql-connector-java</artifactId>

       <version> 8.0 . 19 </version>

     </dependency>

<!--mybatis依赖包-->

     <dependency>

       <groupId>org.mybatis</groupId>

       <artifactId>mybatis</artifactId>

       <version> 3.4 . 2 </version>

     </dependency>

<!--junit依赖包,为什么要用junit依赖包？ @Test 做单元测试用的-->

     <dependency>

       <groupId>junit</groupId>

       <artifactId>junit</artifactId>

       <version> 4.12 </version>

     </dependency>

   </dependencies>

<!--maven静态资源过滤问题：配置报错，不设置会报错：ExceptionInInitializerError-->

   <build>

   <resources>

     <resource>

       <directory>src/main/resources</directory>

       <includes>

         <include>** /*.properties</include>

         <include>**/*.xml</include>

       </includes>

       <filtering>true</filtering>

     </resource>

     <resource>

       <directory>src/main/java</directory>

       <includes>

         <include>**/*.properties</include>

         <include>**/ *.xml</include>

       </includes>

       <filtering> true </filtering>

     </resource>

   </resources>

</build>

package com.kuang.utils;

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 MybatisUtil {

   private static SqlSessionFactory sqlSessionFactory;

   static {

     try {

       String resource = "mybatis-config.xml" ;

       InputStream inputStream = Resources.getResourceAsStream(resource);

       //SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);因为重复定义导致空指针异常

       sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

     } catch (IOException e) {

       e.printStackTrace();

     }

   }

   public static SqlSession getSqlSession(){

     return sqlSessionFactory.openSession();

   }

}

driver=com.mysql.cj.jdbc.Driver

url=jdbc:mysql: //localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai

username=root

password=root

<?xml version= "1.0" encoding= "UTF8" ?>

<!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" >

<!--第一个问题：

com.mysql.jdbc.Driver和mysql-connector-java 5 一起用。

com.mysql.cj.jdbc.Driver和mysql-connector-java 6 + 一起用。

第二个问题：

serverTimezone=Asia/Shanghai 要加时区，不加时区会报错

-->

         <property name= "driver" value= "${driver}" />

         <property name= "url" value= "${url}" />

         <property name= "username" value= "${username}" />

         <property name= "password" value= "${passwprd}" />

       </dataSource>

     </environment>

   </environments>

   <mappers>

     <mapper resource= "com/super/dao/UserMapper.xml" />

   </mappers>

</configuration>

public class User {

   private int id; //id

   private String name;  //姓名

   private String pwd;  //密码

   //构造,有参,无参

   //set/get

   //toString()

}

package com.kuang.dao;

import com.kuang.pojo.User;

import java.util.List;

public interface Mapper {

   List<User> getUserList();

}

<?xml version= "1.0" encoding= "UTF8" ?>

<!DOCTYPE mapper

     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

     "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >

<mapper namespace= "com.super.dao.UserDao" >

   <select id= "getUserList" resultType= "com.kuang.pojo.User" >

   select * from mybatis.user;

  </select>

</mapper>

package com.kuang.dao;

import com.kuang.pojo.User;

import com.kuang.utils.Mybatise;

import org.apache.ibatis.session.SqlSession;

import org.junit.Test;

import java.util.List;

public class UserDaoTest {

   @Test

   public void test(){

     SqlSession sqlSession = MybatisUtil.getSqlSession();

     UserDao mapper = sqlSession.getMapper(Mapper. class );

     List<User> userList = mapper.getUserList();

     for (User user:userList){

       System.out.println(user);

     }

     //sqlSession测试数据mit();增删改需要添加事务

     sqlSession.close();

   }

}