建立石墨碳素网站怎么做百度图片识别搜索引擎

查询user表中所有数据

1. 创建user表，添加数据
2. 导入依赖，创建模块
3. 编写MyBatis核心配置文件
4. 编写SQL映射文件
5. 编写代码
   1. 定义P0J0类
   2. 加载核心配置文件，获取SqlSessionFactory对象
   3. 获取SqlSession对象，执行SQL语句
   4. 释放资源

一、创建user表

use mybatis;  
drop table if exists tb_user;  create table tb_user(  id int primary key auto_increment,  username varchar(20),  password varchar(20),  gender char(1),  addr varchar(30)  
);  insert into tb_user values (1, '张三', '123', '男', '北京');  
insert into tb_user values (2, '李四', '234', '女', '天津');  
insert into tb_user values (3, '王五', '11', '男', '西安');

二、导入依赖

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.16</version>
</dependency>

三、编写MyBatis配置

<!-- 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>  
<environments default="development">  <environment id="development">  <transactionManager type="JDBC"/>  <dataSource type="POOLED">  <!--数据库连接信息-->  <property name="driver" value="org.mariadb.jdbc.Driver"/>  <property name="url" value="jdbc:mariadb://localhost:3306/mybatis"/>  <property name="username" value="root"/>  <property name="password" value="20040927"/>  </dataSource>    </environment></environments>  
<mappers>  <!--加载SQL映射文件-->  <mapper resource="UserMapper.xml"/>  
</mappers>  
</configuration>

四、编写SQL映射文件

<!--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">  
<!--namespace名称空间-->  
<mapper namespace="test">  <select id="selectAll" resultType="cn.cangli.todo.pojo.User">  select * from tb_user;  </select>  
</mapper>

五、编写代码

public class TestUser {  @Test  public void testUser() throws IOException {  //1.加载mybatis的核心配置文件，获取SqlSessionFactory  String resource = "mybatis-config.xml";  InputStream inputStream = Resources.getResourceAsStream(resource);  SqlSessionFactory sqlSessionFactory =  new SqlSessionFactoryBuilder().build(inputStream);  //2.获取SqlSession对象，用他来执行Sql  SqlSession sqlSession = sqlSessionFactory.openSession();  //3.执行Sql  List<User> users = sqlSession.selectList("test.selectAll");  System.out.println(users);  //4.释放资源  sqlSession.close();  inputStream.close();  }  
}

@Mapper //标记Mapper接口
@Select("执行查询语句，返回结果")
@Insert("执行插入语句")
@Update("执行更新语句")
@Delete("执行删除语句")

基于注解的MyBatis

1. 添加依赖: mybatis，mariadb驱动
2. 配置数据库

    spring:datasource:url: jdbc:mariadb://localhost:3306/mybatisusername: rootpassword: rootdriver-class-name: org.mariadb.jdbc.Driver
   

3. 写Mapper

	@Mapperpublic interface UserInfoMapper {@Select("select * from userinfo") //接口方法的实现List<UserInfo> getUserInfoAll();}