If you’re using Object Relational Mapping frameworks like Hibernate, and are using the bi-directional mappings then you can be sure of getting the following errors if you try to generate JSON of the entities involved.
1. If you’re using Jackson
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com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) |
2. If you’re using Google’s Gson
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java.lang.IllegalStateException: circular reference error |
Let’s take a case of two entities Actor, and Movie having a bi-directional relationship and using them we’ll see how to get over the above exceptions when we try to generate JSON.
This solution uses Jackson for generating JSON.
So if you’re using Google’s Gson you’ll have to write an exclusion strategy yourself, and more importantly the rest of the post is useless for you, unless you’re willing to switch to Jackson like I did with such great finesse! ;)
If yes, then you can download Jackson’s libraries and continue reading the post further, rest assured that it’ll be of immense help to you! :)
Now, these entities will have a many-to-many relationship amongst them. As one Actor can act in many Movies and one Movie can have many Actors (as it so often happens, and by the way due apologies for being trite and rhetoric!).
Actor.java
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@Entity@Table(name="Actor")public class Actor implements Serializable { . . . /* This is the exception-saving-annotation */ @JsonManagedReference @ManyToMany private List<Movie> movies; . . .} |
Movie.java
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@Entity@Table(name="Movie")public class Movie implements Serializable { . . . /* This is the exception-saving-annotation */ @JsonBackReference @ManyToMany(mappedBy="movies") private List<Actor> actors; . . .} |
So all we did was adding two annotations to the fields having a relationship.
- @JsonManagedReference: This annotation should be put on the owner of the relationship, or as you may deem fit.
- @JsonBackReference: This annotation should be used on the other end of the relationship.
Now, having done that it’s extremely easy to generate the JSON.
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//com.fasterxml.jackson.databind.ObjectMapperObjectMapper objectMapper = new ObjectMapper();//The input argument of the writeValueAsString() function can be a bean, array, list, map or a set.String actorsAsJson = objectMapper.writeValueAsString(actorsList);//actorsList is a variable of type List<Actor>//Voila! You're done! |
That’s all for the circular dependency errors.
source ：https://ankeetmaini.wordpress.com/2012/07/26/json-troubleshooting-circular-dependency-errors/