一、Spring Boot连接MySQL数据库

使用mybatis连接MySQL数据库，在prm.xml中添加配置依赖

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.1</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

在application.properties中添加数据库配置

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=用户名
spring.datasource.password=密码
spring.datasource.url=jdbc:mysql://localhost:3306/库名?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=true

二、编写MySQL表对应的实体类

package com.jackie.adminjava;

public class Student {
    Integer id;
    String name;
    public void setId(Integer id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public Integer getId() { return id; }
    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + ''' +
                '}';
    }
}

三、编写实体类对应的Mapper

package com.jackie.adminjava;

import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;
import org.apache.ibatis.annotations.Mapper;

@Mapper
@Repository
public interface StudentMapper {
    @Select("select * from students where id = #{id}")
    Student findById(Integer id);
}

四、编写实体类对应的Service

package com.jackie.adminjava;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class StudentService {
    @Autowired
    StudentMapper studentMapper;

    public Student findStudent(Integer id) {
        return studentMapper.findById(id);
    }
}

五、编写实体类对应的Controller

package com.jackie.adminjava;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class StudentController {
    @Autowired
    StudentService studentService;

    @GetMapping("/student")
    public String student(@RequestParam Integer num) {
         Student student = studentService.findStudent(num);
         return student.toString();
    }
}

启动项目后在请求接口 /student?num=1 就可以请求到数据。

总结

• 依赖配置不可缺少，注意版本之间的差异。
• 实体类是对数据库的一种映射关系，负责对数据库数据进行组装。
• Mapper是对数据库数据进行查询。
• Service是对请求参数和其他业务逻辑进行处理。
• Controller接口定义，接收请求参数。