用戶從頁面前端，也就是我們所說的 view 層進行查詢訪問，進入到 controller 層找到對應的接口，接 著 controller 進行對 service 層進行業務功能的調用，service 要進入 dao 層查詢數據，dao 層調用 mapper.xml 文件生成 sql 語句到數據庫中進行查詢

2.1、準備數據庫user表插入四條數據

2.2、model下創建一個User類

與數據庫的字段一一對應

@Getter @Setterpublic class User { private int id; private String username; private String password; private int age;}

2.3、dao下創建一個UserDao接口

@Repository注解修飾哪個類，則表明這個類具有對對象進行CRUD（增刪改查）的功能

@Repositorypublic interface UserDao { public User getUserById(@Param('id') int id); public List<User> getUserByAge(@Param('age') int age); public List<User> getUserByName(@Param('username') String username); public int insertUser(@RequestBody User user);}

通過UserMapping.xml配置文件實現UserDao接口

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE mapperPUBLIC '-//mybatis.org//DTD Mapper 3.0//EN''http://mybatis.org/dtd/mybatis-3-mapper.dtd'><mapper namespace='com.example.demo.dao.UserDao'> <select resultType='User'>select * from `user` where id=#{id} </select> <select resultType='User'>select * from `user` where age=#{age} </select> <select resultType='User'>select * from `user` where username like concat(’%’,#{username},’%’) </select> <insert parameterType='User'><selectKey keyProperty='id' order='AFTER' resultType='int'> SELECT LAST_INSERT_ID()</selectKey>insert into user (username, password, age)values (#{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER}) </insert></mapper>

2.4、Service下創建一個UserService接口

public interface UserService { public User queryUserById(int id); public List<User> queryUserByAge(int age); public List<User> queryUserByName(String username); public int insertUser(User user);}

再創建一個UserServiceImpl實現UserService

@Servicepublic class UserSeviceImpl implements UserService { @Autowired private UserDao userDao; @Override public User queryUserById(int id) {return userDao.getUserById(id); } @Override public List<User> queryUserByAge(int age) {return userDao.getUserByAge(age); } @Override public List<User> queryUserByName(String username) {return userDao.getUserByName(username); } @Override public int insertUser(User user) {return userDao.insertUser(user); }}

2.5、controller下創建一個UserController

@GetMapping是代表該查詢接口用的是get方式@RequestMapping(value='/insert',method = RequestMethod.POST)代表該插入接口用post方式

@RestControllerpublic class UserController { @Autowired private UserService userService; @GetMapping('/userid') public User getUserById(@RequestParam('id') int id){return userService.queryUserById(id); } @GetMapping('/username') public List<User> getUserByUsername(@RequestParam('username') String username){return userService.queryUserByName(username); } @RequestMapping(value='/insert',method = RequestMethod.POST) public User insertUser(@RequestBody User user){int x = userService.insertUser(user);return user; }}

2.6、application.yml文件連接數據庫

server: port: 8080spring: datasource: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://localhost:3306/testingdev9?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai username: root password: 123456mybatis: mapper-locations: - classpath:mapper/*.xml - classpath*:com/**/mapper/*.xml type-aliases-package: com.example.demo.model

2.7、啟動DemoApplication文件

出現Started DemoApplication代表啟動成功了

2.8、使用postman調用接口

如下圖根據id查詢

如下圖插入數據

可以看到數據庫多了一條數據

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