Java JPA Hibernate - 错误：无限递归答案

【问题标题】：Java JPA Hibernate - Error: Infinite recursionJava JPA Hibernate - 错误：无限递归
【发布时间】：2016-10-09 14:13:40
【问题描述】：

我有 3 个实体（产品、提供商和价格），其中价格与其他 2 个相关联。一个产品可以有多个价格，每个提供商一个价格：

产品类别：

@Entity
@Table(name = "products") 
public class Product implements java.io.Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "product_id")
private int id;

@Column(name = "product_category")
private String productCategory;

@Column(name = "product_subcategory")
private String productSubcategory;

@Column(name = "product_name")
private String productName;

@Column(name = "product_description")
private String productDescription;

@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.product", cascade=CascadeType.ALL)
private Set<Prices_1> prices_1 = new HashSet<Prices_1>(0);


public Set<Prices_1> getPrices_1(){
    return prices_1;
}

public void setPrices_1(Set<Prices_1> prices_1){
    this.prices_1 = prices_1;
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getProductCategory() {
    return productCategory;
}

public void setProductCategory(String productCategory) {
    this.productCategory = productCategory;
}

public String getProductSubcategory() {
    return productSubcategory;
}

public void setProductSubcategory(String productSubcategory) {
    this.productSubcategory = productSubcategory;
}

public String getProductName() {
    return productName;
}

public void setProductName(String productName) {
    this.productName = productName;
}

public String getProductDescription() {
    return productDescription;
}

public void setProductDescription(String productDescription) {
    this.productDescription = productDescription;
}

@Override
public String toString() {
    return "ProductController [id=" + id + ", productName=" + productName
            + ", productCategory=" + productCategory + ", productSubcategory=" + productSubcategory
            + ", productDescription=" + productDescription
            + "]";
}

}

提供者类：

@Entity
@Table(name="providers")
public class Provider implements java.io.Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name="provider_id")
private int id;

@Column(name="provider_name")
private String providerName;

@Column(name="provider_address")
private String providerAddress;

@Column(name="provider_phone")
private String providerPhone;

@Column(name="provider_archived")
private int providerArchived = 0;

@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.provider")
private Set<Prices_1> prices_1 = new HashSet<Prices_1>(0);

public Set<Prices_1> getPrices_1() {
    return prices_1;
}

public void setPrices_1(Set<Prices_1> prices_1) {
    this.prices_1 = prices_1;
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getProviderName() {
    return providerName;
}

public void setProviderName(String providerName) {
    this.providerName = providerName;
}

public String getProviderAddress() {
    return providerAddress;
}

public void setProviderAddress(String providerAddress) {
    this.providerAddress = providerAddress;
}

public String getProviderPhone() {
    return providerPhone;
}

public void setProviderPhone(String providerPhone) {
    this.providerPhone = providerPhone;
}

public int getProviderArchived() {
    return providerArchived;
}

public void setProviderArchived(int providerArchived) {
    this.providerArchived = providerArchived;
}

@Override
public String toString() {
    return "ProviderController [id=" + id + ", providerName=" + providerName
            + ", providerAddress=" + providerAddress + ", providerPhone="
            + providerPhone + "]";
}

}

Prices_1 类：

@Entity
@Table(name = "prices_1")
@AssociationOverrides({
    @AssociationOverride(name = "pk.product",
            joinColumns = @JoinColumn(name = "product_id")),
    @AssociationOverride(name = "pk.provider",
            joinColumns = @JoinColumn(name = "provider_id"))})
public class Prices_1 implements java.io.Serializable {

@EmbeddedId
private PricesId pk = new PricesId();

@Column(name = "price")
private float price;

public PricesId getPk() {
    return pk;
}

public void setPk(PricesId pk) {
    this.pk = pk;
}

public float getPrice() {
    return price;
}

public void setPrice(float price) {
    this.price = price;
}

@Transient
public Product getProduct() {
    return getPk().getProduct();
}

public void setProduct(Product product) {
    getPk().setProduct(product);
}

@Transient
public Provider getProvider() {
    return getPk().getProvider();
}

public void setProvider(Provider provider) {
    getPk().setProvider(provider);
}


public boolean equals(Object o) {
    if (this == o)
        return true;
    if (o == null || getClass() != o.getClass())
        return false;

    Prices_1 that = (Prices_1) o;

    if (getPk() != null ? !getPk().equals(that.getPk())
            : that.getPk() != null)
        return false;

    return true;
}

public int hashCode() {
    return (getPk() != null ? getPk().hashCode() : 0);
}

}

PricesID 类：

@Embeddable
public class PricesId implements java.io.Serializable {

@ManyToOne
private Product product;

@ManyToOne
private Provider provider;

public Product getProduct() {
    return product;
}

public void setProduct(Product product) {
    this.product = product;
}

public Provider getProvider() {
    return provider;
}

public void setProvider(Provider provider) {
    this.provider = provider;
}

public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    PricesId that = (PricesId) o;

    if (product != null ? !product.equals(that.product) : that.product != null) return false;
    if (provider != null ? !provider.equals(that.provider) : that.provider != null) return false;

    return true;
}

public int hashCode() {
    int result;
    result = (product != null ? product.hashCode() : 0);
    result = 31 * result + (provider != null ? provider.hashCode() : 0);
    return result;
}

}

ProductsRepository 类：

@Repository
public class ProductsRepository {

@PersistenceContext
EntityManager em;

public List<Product> findAllProducts(){
    Query query = em.createQuery("SELECT e FROM Product e");
    return (List<Product>) query.getResultList();
}

}

ProductsService 类：

@Service
public class ProductsService {

@Autowired
ProductsRepository productsRepository;

@Transactional(readOnly = true)
public List<Product> findAllProducts(){
    List<Product> pv = productsRepository.findAllProducts();
    return pv;
}

}

ProductsController 类：

@Controller
@RequestMapping("product")
public class ProductController {

@Autowired
private ProductsService productsService;

@ResponseBody
@ResponseStatus(HttpStatus.OK)
@RequestMapping(method = RequestMethod.GET)
public List<Product> getProducts(){
    List<Product> productList = productsService.findAllProducts();
    for (Product p : productList){
        System.out.println("Andres. Provider name: " + p.getProductName());
    }
    return productList;
}
}

控制器返回的ArrayList产品列表：

问题是 Products[0] 有 2 个价格_1。 Price_1[0] 关联了 Product 和 Provider，两者都关联了 Price_1 等。最终陷入无限循环

任何想法如何获得以下对象：产品列表，每个产品都有一个价格列表，每个供应商一个价格。

谢谢！

编辑： 问题不在于创建的 ArrayList productList，当 productList 对象返回到浏览器时会触发错误：

【问题讨论】：

您如何将其返回到浏览器？ - 这可能是因为当它被转换为 json 时，调用了 toString() 方法，该方法试图序列化在 prices_1 中定义的产品和提供者。尝试在 priceid 类中将产品和提供者定义为瞬态。
非常感谢您的快速回复@PushpendraPal。我并返回浏览器“return productList;” （ArrayList 产品列表）。我在 PriceId.java 中的 Product 和 Provider 对象中都添加了“@Transient”，但应用程序没有运行：“PricesId 没有持久的 id 属性：....model.Prices_1.pk”。自动序列化是我首先关心的问题，这就是我覆盖所有 toString() 方法（产品、提供者和价格_1）的原因。
hmm... 我认为在产品和提供者上覆盖 toString() 将不起作用，因为当您返回 productList 时，将在列表上调用 toString()（您的产品的 java.util.List ）。它没有被覆盖，并且仍然会查找列表中所有对象的序列化......我还观察到 toString 没有被覆盖为 prices_1 .....
嗨@PushpendraPal，我在 Price_1 类中添加了“@Override toString()”，但没有任何区别。
您可以尝试创建产品的通用列表。我在答案下面给出的泛型.. 然后通过在 GenericClass 对象上使用 toString 从控制器返回字符串...您可以向此 GenericClass 添加其他未实现的方法，但无需为这些提供实现

标签： java hibernate jpa

【解决方案1】：

public class GenericClass<E> implements List<E> {

private List<E> list;
public GenericClass() {
    this.list = new ArrayList<>();
}


@Override
public String toString() {
    StringBuilder s = new StringBuilder();
    for (E e : list) {
        s.append(e.toString());
    }
    return s.toString();
}

@Override
public boolean add(E e) {

    return list.add(e);
}

@Override
public boolean addAll(Collection<? extends E> c) {

    return list.addAll(c);
}

}

【讨论】：

【解决方案2】：

我创建了 3 个数据传输对象来自定义和协调列表 productList：

public class ProductsDTO {

private List<ProductDTO> productDTOSet = new ArrayList<ProductDTO>(0);

public ProductsDTO(List<ProductDTO> productDTOSet) {
    this.productDTOSet = productDTOSet;
}

public static ProductsDTO mapFromProductSetEntity(List<Product> products){
    List<ProductDTO> productDTOs = new ArrayList<ProductDTO>(0);
    for (Product p : products) {
        productDTOs.add(ProductDTO.mapFromProductEntity(p));
    }
    return new ProductsDTO(productDTOs);
}

public class ProductDTO {

private int id;
private String productCategory;
private String productSubcategory;
private String productName;
private String productDescription;
private Set<PriceDTO> prices = new HashSet<PriceDTO>(0);


public ProductDTO(int id, String productCategory, String productSubcategory, String productName,
                  String productDescription, Set<PriceDTO> prices) {
    this.id = id;
    this.productCategory = productCategory;
    this.productSubcategory = productSubcategory;
    this.productName = productName;
    this.productDescription = productDescription;
    this.prices = prices;
}

public static ProductDTO mapFromProductEntity(Product product){

    Set<PriceDTO> priceDTOs = new HashSet<PriceDTO>(0);
    for (Prices_1 p1 : product.getPrices_1()){
        priceDTOs.add(PriceDTO.mapFromPrice_1Entity(p1));
    }

    return new ProductDTO(product.getId(), product.getProductCategory(), product.getProductSubcategory()
    , product.getProductName(), product.getProductDescription(), priceDTOs);
}
}

public class PricesDTO {

private Set<PriceDTO> pricesDTO = new HashSet<PriceDTO>(0);

public Set<PriceDTO> getPricesDTO() {
    return pricesDTO;
}

public void setPricesDTO(Set<PriceDTO> pricesDTO) {
    this.pricesDTO = pricesDTO;
}
}

然后将 List productList 映射到 DTO：

@Controller
@RequestMapping("product")
public class ProductController {

@Autowired
private ProductsService productsService;

@ResponseBody
@ResponseStatus(HttpStatus.OK)
@RequestMapping(method = RequestMethod.GET)
public ProductsDTO getProducts(){
    List<Product> productList = productsService.findAllProducts();
    for (Product p : productList){
        System.out.println("Andres. Provider name: " + p.getProductName());
    }

    return ProductsDTO.mapFromProductSetEntity(productList);
}
}

结果如下：

【讨论】：