Spring Data JPA, error while sending data to postman from Rest Controller, Nested exception

Question

I got this error when I was trying to send data, in form of a List Object from Rest Controller to postman. I know what caused this problem but don't know how to solve it? code for the Rest Entity and Controller is as follows:

@Entity
@Table(name = "posts")
public class PostEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;
    @OneToMany(mappedBy = "postEntity")
    private List<CommentEntity> comments;

    // getters and setters below
}

@Entity
@Table(name = "comments")
public class CommentEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE,CascadeType.DETACH, CascadeType.REFRESH})
    @JoinColumn(name = "post_id")
    private PostEntity postEntity;
   
    // getters and setters 
}

public List<PostEntity> getFilteredData() {
    List<PostEntity> posts = postService.findAll();
    return posts;
}

Error Message:

2021-02-11 20:03:57.417 ERROR 26199 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    
: Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.http.converter.HttpMessageNotWritableException:
 Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) 
(through reference chain: 

com.akashmjain.BlogApplication.enitity.UserEntity["posts"]->org.hibernate.collection.internal.Pe
rsistentBag[0]->com.akashmjain.BlogApplication.enitity.PostEntity["author"]->com.akashmjain.Blog
Application.enitity.UserEntity["posts"]->org.hibernate.collection.internal.PersistentBag[0]->com
.akashmjain.BlogApplication.enitity.PostEntity["author"]->com.akashmjain.BlogApplication.enitity.UserEntity["posts"]->org.hibernate.collection.internal.PersistentBag[0]->com.akashmjain.BlogApp
lication.enitity.PostEntity["author"]->
com.akashmjain.BlogApplication.enitity.UserEntity["posts"]->org.hibernate.collection.internal.PersistentBag[0]->com.akashmjain.BlogApplication.enitity.Po
stEntity["author"]->com.akashmjain.BlogApplication.enitity.UserEntity["posts"]->org.hibernate.collection.internal.PersistentBag[0]->com.akashmjain.BlogApplication.enitity.PostEntity["author"]-
>com.akashmjain.BlogApplication.enitity.UserEntity["posts"]->org.hibernate.collection.internal.PersistentBag[0]->com.akashmjain.BlogApplication.enitity.PostEntity["author"]-

Here I think the problem is The Comment and Post Entity calling each other getters to send the data to the rest controller. So I tried changing the toString() to only have Primitive types and wrapper classes. but still, there is the same error. Am I write on this or is there something I am missing?

Answer 1

You have a unidirectional relation between the two entities which makes Jackson fail to serialize/deserialize the payload due to the infinite recursion.

You can try the following that will hopefully resolve the issue:

@OneToMany(mappedBy = "postEntity")
@JsonBackReference
private List<CommentEntity> comments;

Annotate the list of comments using @JsonBackReference and then do the following on the CommentEntity but this time use the following annotation:

@JoinColumn(name = "post_id")
@JsonManagedReference
private PostEntity postEntity;

You can check on more on that here https://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion