[Java] 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();
  }
}

{
    code: 200,
    message: "查询成功",
    data: [{ name:"lxc", age: 20 }, { name: "123", age: 100 }]
}

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;
  }
}