在 Springboot 中获取服务 NULL 值的请求 REST API

Question

I'm fairly new to spring boot and Java, I've been working on a REST API using springboot for an ecommerce project but for some reason I can't get the products from the database, my products are getting saved to the database but whenever I fetch them the fields show up as null values. this is what I get when I use GET using Postman.

My controller and other files are as follows.

package com.ecommerce.ecommerceappapi.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.ecommerce.ecommerceappapi.model.Product;
import com.ecommerce.ecommerceappapi.services.ProductService;

@CrossOrigin(origins = "http://localhost:3000")
@RestController
@RequestMapping("api/v1/")
public class ProductController {

    @Autowired
    private final ProductService productService;
    
    public ProductController(ProductService productService) {
        this.productService = productService;
    }
    
    @PostMapping("/products")
    public Product createProduct(@RequestBody Product product) {
        return productService.createProduct(product);
    }
    
    @GetMapping("/products")
    public List<Product> getAllProducts() {
        return productService.getAllProducts();
    }
    
}

Entity ->

package com.ecommerce.ecommerceappapi.entity;

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

import lombok.Data;

@Entity
@Data
@Table(name="products")
public class ProductEntity {
    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    private long prodId;
        
    private String productName;
    private int productPrice;
    private String productDesc;
    private String productData;
    
    public String getProductName() {
        return productName;
    }
    public void setProductName(String productName) {
        this.productName = productName;
    }
    public int getProductPrice() {
        return productPrice;
    }
    public void setProductPrice(int productPrice) {
        this.productPrice = productPrice;
    }
    public String getProductDesc() {
        return productDesc;
    }
    public void setProductDesc(String productDesc) {
        this.productDesc = productDesc;
    }
    public String getProductData() {
        return productData;
    }
    public void setProductData(String productData) {
        this.productData = productData;
    }
    public Long getProdId() {
        // TODO Auto-generated method stub
        return prodId;
    }
}

Service Interface ->

package com.ecommerce.ecommerceappapi.services;

import java.util.List;

import com.ecommerce.ecommerceappapi.model.Product;

public interface ProductService {
    Product createProduct(Product product);
    List<Product> getAllProducts();
}

Service Implementation ->

package com.ecommerce.ecommerceappapi.services;


import java.util.List;
import java.util.stream.Collectors;

import org.springframework.beans.BeanUtils;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Service;

import com.ecommerce.ecommerceappapi.entity.ProductEntity;
import com.ecommerce.ecommerceappapi.model.Product;
import com.ecommerce.ecommerceappapi.repository.ProductRepository;


@Service
public class ProductServiceImpl implements ProductService {

    private ProductRepository productRepository;
    
    public ProductServiceImpl(ProductRepository productRepository) {
        super();
        this.productRepository = productRepository;
    }

    @Override
    public Product createProduct(Product product) {
        // TODO Auto-generated method stub
        ProductEntity productEntity = new ProductEntity();
        BeanUtils.copyProperties(product, productEntity);
        productRepository.save(productEntity);
        return product;
    }
    
    @Override
    public List<Product> getAllProducts(){
        
        List<ProductEntity> productEntities =  productRepository.findAll();
        
        List<Product> products = productEntities.stream().map(product -> new Product(
                product.getProdId(), 
                product.getProductName(), 
                product.getProductPrice(),
                product.getProductDesc()))
                .collect(Collectors.toList());
        
        return products;
        }


}

Repository ->

package com.ecommerce.ecommerceappapi.repository;

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

import com.ecommerce.ecommerceappapi.entity.ProductEntity;

@Repository
public interface ProductRepository extends JpaRepository<ProductEntity, Long> {

}

Product ->

package com.ecommerce.ecommerceappapi.model;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

//import java.util.List;
import lombok.Data;


@Data
@AllArgsConstructor
@NoArgsConstructor
public class Product {
    private long prodId;
    private String productName;
    private int productPrice;
    private String productDesc;
    private String productData;
    

    
    public Product(Long prodId2, String productName2, int productPrice2, String productDesc2) {
        // TODO Auto-generated constructor stub;
        return; 
    }
    public long getProdId() {
        return prodId;
    }
    public void setProdId(long prodId) {
        this.prodId = prodId;
    }
    public String getProductName() {
        return productName;
    }
    public void setProductName(String productName) {
        this.productName = productName;
    }
    public int getProductPrice() {
        return productPrice;
    }
    public void setProductPrice(int productPrice) {
        this.productPrice = productPrice;
    }
    public String getProductDesc() {
        return productDesc;
    }
    public void setProductDesc(String productDesc) {
        this.productDesc = productDesc;
    }
    public String getProductData() {
        return productData;
    }
    public void setProductData(String productData) {
        this.productData = productData;
    }
    

}

I figure the Product class is causing the issue as the method

public Product(Long prodId2, String productName2, int productPrice2, String productDesc2) {
        // TODO Auto-generated constructor stub;
        return; 
    }

does not return anything, otherwise I'm totally lost as to what might be the issue here.

Answer 1

I think the problem with your code is in your Product class. In the service you fetch all ProductEntity from the database and for each one you create a new Product object. The problem is when you create the Product object. You call the constructor:

public Product(Long prodId2, String productName2, int productPrice2, String productDesc2) {
        // TODO Auto-generated constructor stub;
        return; 
    }

In this constructor you never assign values to attributes of Product class. You should remove this constructor and put this one:

public Product(Long prodId, String productName, int productPrice, String productDesc) {
        this.prodId = prodId;
        this.productName = productName;
        this.productPrice = productPrice;
        this.productDesc = productDesc;
    }

In the constructor, you should always use this. ATTRIBUT_NAME to assign values and store them in the class.

Answer 2

I think you should remove the return from the constructor. and if you have @Data and @AllArgsConstructor Lombok annotations you don't have to explicitly generate getters, setters and the constructor.

And I would prefer

@Override
    public List<Product> getAllProducts(){
        
        List<ProductEntity> productEntities =  productRepository.findAll();
        
        List<Product> products = productEntities.stream()
                                       .map(Product::new)
                                       .collect(Collectors.toList());
        return products;
    }

And from the Product class will look like this

public Product(ProductEntity productEntity) {
        this.prodId = productEntity.getProdId();
        this.productName = productEntity.getProductName();
        this.productPrice = productEntity.getProductPrice();
        this.productDesc = productEntity.ProductDesc();
   }