Springboot连接数据库及查询数据完整流程

# 增加数据库连接
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/spring?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=utf8&useSSL=false
spring.datasource.username=root
spring.datasource.password=lvxingchen
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

package com.lxc.springboot.domain;
 
public class User {
    private int id;
    private String user;
    private String name;
    private int age;
    private String password;
 
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", user='" + user + '\'' +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", password='" + password + '\'' +
                '}';
    }
 
    public int getId() {
        return id;
    }
 
    public void setId(int id) {
        this.id = id;
    }
 
    public String getUser() {
        return user;
    }
 
    public void setUser(String user) {
        this.user = user;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public String getPassword() {
        return password;
    }
 
    public void setPassword(String password) {
        this.password = password;
    }
}

package com.lxc.springboot.mapper;
 
import com.lxc.springboot.domain.User;
 
import java.util.List;
 
public interface UserMapper {
    public List<User> getUserList();
}

@ComponentScan("com.lxc.springboot")
@SpringBootApplication
@MapperScan("com.lxc.springboot.mapper") // 让springboot知道mapper是这个项目的持久层
public class BootAndVueProjectApplication {
    private static final Logger LOG = LoggerFactory.getLogger(BootAndVueProjectApplication.class);
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(BootAndVueProjectApplication.class);
        //  SpringApplication.run(BootAndVueProjectApplication.class, args);
        Environment env = app.run(args).getEnvironment();
        LOG.info("启动成功!");
        LOG.info("地址：\thttp://127.0.0.1:{}", env.getProperty("server.port"));
    }
}

<?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" >
 
<!--接口-->
<!--
namespace:对应接口的全路径；
id：对应接口的方法；
resultType：结果类型。
-->
<mapper namespace="com.lxc.springboot.mapper.UserMapper" >
    <select id="getUserList" resultType="com.lxc.springboot.domain.User">
        select id, user, name, age, password from user
    </select>
 
</mapper>

# 配置mybatis所有的Mapper.xml所在的路径
mybatis.mapper-locations=classpath:/mapper/**/*.xml

package com.lxc.springboot.service;
 
import com.lxc.springboot.domain.User;
import com.lxc.springboot.mapper.UserMapper;
import org.springframework.stereotype.Service;
 
import javax.annotation.Resource;
import java.util.List;
/**
 * service层调用持久层
 * @Service // 让spring扫描到这个包
 *
 * @Autowired和@Resource
 * 两个注解都可以把一个类注入进来（相当于import）
 * Resource JDK自带的
 * Autowired spring自带的
 */
@Service // 让spring扫描到这个包
public class UserService {
    @Resource
    public UserMapper userMapper;
    public List<User> getList() {
        return userMapper.getUserList();
    }
}

package com.lxc.springboot.controller;
 
import com.lxc.springboot.commonResponse.ComResponse;
import com.lxc.springboot.service.UserService;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
 
import javax.annotation.Resource;
 
@RestController // 通常返回一个json或 字符串
//@Controller // 一般是返回一个页面
public class TestController {
 
    @Resource // 把service层userService注入进来
    private UserService userService; 
 
    // 调用service层
    @RequestMapping(value = "/service")
    public ComResponse getService() {
        ComResponse<List<User>> objComResponse = new ComResponse<>();
        List<User> userList = userService.getList();
        objComResponse.setData(userList);
        objComResponse.setMsg("返回成功")
        return objComResponse;
    }
}

package com.lxc.springboot.commonResponse;
/**
 *
 * @param <T>
 *     ComResponse 是一个泛型类，返回的是一个泛型，外界可以传入任何类型的值
 *     理解泛型：
 *     有点像js方法，你给它传任何类型都可以,但是最后返回的类型是setData时候传的对象！！！
 */
public class ComResponse<T> {
 
    private String msg = "返回成功";
    private int code = 200;
    private T data;
 
    public String getMsg() {
        return msg;
    }
 
    public void setMsg(String msg) {
        this.msg = msg;
    }
 
    public int getCode() {
        return code;
    }
 
    public void setCode(int code) {
        this.code = code;
    }
 
    public T getData() {
        return data;
    }
 
    public void setData(T data) {
        this.data = data;
    }
}