当我在本地浏览器上请求时，如何以json值的形式访问数据库？

Question

注意：这是一个与其他表上的数据库有连接的项目。我刚做了一个新表，但我的代码一定有问题，因为我不能得到我想要的东西。我有一个city表，这个表有3列，分别命名为id、name、city_id。并且我导入了一个csv文件，所以当我查询的时候，我可以看到一些数据。

我在Eclipse上用Java编写了实体、存储库、控制器和服务

我该怎么办？例如，当我像localhost:8181/mfc/city/getallcities那样搜索时，它应该将所有城市作为json提供给我

你能告诉我应该补充些什么吗？

city.java

package com.mfc.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="city")
public class City{
    
    @Id
    @Column(name="id")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    int id;
    
    @Column(name="city_name")
    String cityName;
    
    @Column(name="city_id")
    int cityId;
    
    public City() {
        super();
    }
    
    public City(int id, String cityName, int cityId) {
        super();
        this.id = id;
        this.cityName = cityName;
        this.cityId = cityId;
    }
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getCityName() {
        return cityName;
    }
    
    public void setCityName(String cityName) {
        this.cityName = cityName;
    }
    
    public int getCityId() {
        return cityId;
    }
    
    public void setCityId(int cityId) {
        this.cityId = cityId;
    }
}

CityController.java

package com.mfc.admin.controller;
import java.util.List;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.mfc.admin.service.CityService;
import com.mfc.entity.City;

@RestController
@RequestMapping("/city")
public class CityController {
    
    private static final Logger logger = LogManager.getLogger(CityController.class);

    @Autowired
    CityService cityService;
    
    @RequestMapping(value="/getAllCities", method=RequestMethod.GET, headers = "Accept=application/json")
    public List getCities() {
        logger.trace("CityController: getAllCities begins");
        List listOfCities = cityService.getAllCities();
        
        logger.trace("CityController: getAllCities ends");
        return listOfCities;
    }
    
    
    @RequestMapping(value="/getCity/{id}", method=RequestMethod.GET, headers = "Accept=application/json")
    public City getCityById(@PathVariable int id) {
        return cityService.getCity(id);
    }
    
}

CityService.java

package com.mfc.admin.service;    

import java.util.List;

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

import com.mfc.entity.City;
import com.mfc.repository.CityRepository;

@Service("cityService")
public class CityService {
    
    @Autowired
    CityRepository cityDTO;
    
    @Transactional
    public List getAllCities() {
        return cityDTO.getAllCities();
    }
    
    @Transactional
    public City getCity(int id) {
        return cityDTO.getCity(id); // getCity is red here, there is mistake i guess
    }
    
}

CityRepository.java

package com.mfc.repository;

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;

import com.mfc.entity.City;

public interface CityRepository extends JpaRepository<City, Integer>{

    List getAllCities();
    City getCity();
    
}

Answer 1

在CityRepository中没有方法getCity（id）。在CityService中，尝试使用自动生成的方法，如下所示：

返回CityDTo.findById(id)；

这个方法是存在的，因为存储库扩展了jparepository 。这告诉Spring Data生成一组标准CRUD方法。