Java object graph to JSON conversion, with cycles

Question

How to convert a Java object graph to JSON, where the graph has circular dependencies / cycles?

Answer 1

There are many open source libraries that can generate JSON. Jersey can break the circular dependencies. For others you might want to google.

• Jersey (Use @JsonIgnore instead of @XmlTransient to break the circular dependency)
• Gson (doesn't support circular references. there is a open defect created for this)
• Jackson (Handle bi-directional references using declarative methods)
• flexjson (claims it supports circular references)

Answer 2

Note: this answer was written a long time ago. Use Gson, Jersey or Jackson.

I went with json-simple on my last project. It doesn't bring in any unneeded project dependencies (such as apache-commons jars) and was enough to parse/generate JSON correctly.

You'll still have to manage circular references yourself. I really doubt there is such a library that is built to handle this. You can do this easily by added to a Set any objects that you convert, and then just checking to see if the object you're about to convert is in the set.

Also, I don't think json-simple automatically serializes an object; that is, you have to feed it the data you want added to the JSON. It just handles all of the messy formatting for you.