无法获取 json：无限递归答案

【问题标题】：Could not GET json : Infinite recursion无法获取 json：无限递归
【发布时间】：2020-07-23 07:39:04
【问题描述】：

我在尝试对发布者存储库执行 GET 时遇到无限循环。

出版商：

@Data
@AllArgsConstructor
@Entity
@Table(name = "publisher")
public class Publisher {

    @Id
    private Long publisherID;

    private String name;
    private String location;

    public Publisher(@JsonProperty("publisherID") Long publisherID,
                     @JsonProperty("name") String name,
                     @JsonProperty("location") String location) {
        this.publisherID = publisherID;
        this.name = name;
        this.location = location;
    }

    @JsonManagedReference(value="Book-Publisher")
    @OneToMany(mappedBy = "publisher", cascade = CascadeType.ALL)
    private Set<Book> books;

    public Publisher() {
    }
}

书：

@Data
@AllArgsConstructor
@Entity
@Table(name = "book")
public class Book {

    @Id

私有长ID；

private String name;

@JsonBackReference(value="Book-Publisher")
@ManyToOne
@JoinColumn(name="publisherID")
private Publisher publisher;

private int publicationYear;
private int amount;

@JsonManagedReference(value="BookAuthors-Book")
@OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
private Set<BookAuthors> bookAuthors;

@JsonManagedReference(value="BookGenres-Book")
@OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
private Set<BookGenres> bookGenres;

public Book(@JsonProperty("id") Long id,
            @JsonProperty("name") String name,
            @JsonProperty("publisherID") Long publisherID,
            @JsonProperty("publicationYear") int publicationYear,
            @JsonProperty("amount") int amount) {
    this.id = id;
    this.name = name;
    this.publicationYear = publicationYear;
    this.amount = amount;
    PublisherService publisherService = BeanUntil.getBean(PublisherService.class);
    this.publisher = publisherService.findByID(publisherID).get();

}
@JsonManagedReference(value="RentedBook-Book")
@OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
private Set<RentedBook> rentedBooks;

public Book() {
}

}

2020-04-10 16:43:02.483 WARN 672 --- [nio-8080-exec-6] .wsmsDefaultHandlerExceptionResolver：已解决 [org.springframework.http.converter.HttpMessageNotWritableException：无法写入 JSON：无限递归（堆栈溢出错误）；嵌套异常是 com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (通过引用链: java.util.ArrayList[0]->com.vanyasav.domain.Publisher["books"])]

这里有完整的代码：

https://github.com/vanyasav/Library

【问题讨论】：

标签： java json spring

【解决方案1】：

当Publisher的列表被序列化为响应时，Publisher字段的所有getter方法被调用。所以，Publisher 关系字段books 的getter 也被调用来设置值。这是递归发生的。这就是无限递归的原因。

最好不要使用实体作为响应。为发布者创建一个 DTO 类，然后将发布者实体值映射到 DTO 中，然后发送响应。

要将一个模型动态映射到另一个模型，您可以使用ModleMapper

【讨论】：

是的，谢谢，ModelMapper 解决方案运行良好。