How to serialize a java.util.List to Json using Gson Library?

Question

In my servlet I have the following code:

    response.setContentType("application/json");//set json content type
    PrintWriter out = response.getWriter();

   EntityManagerFactory emf=Persistence.createEntityManagerFactory("webPU");
   GpsJpaController gjc=new GpsJpaController(emf);    
   java.util.List<Gps> listGps=gjc.findGpsEntities();//retrieve the list of GPS from DB 

   Gson gson=new Gson();
   String json=gson.toJson(listGps); //convert List<Gps> to json
   out.println(json);

response is returned from ajax with this code:

$.ajax({ 
           type: "GET", 
           url: "getInfoGeoActive",
           dataType: 'json',
           error: function(xhr, ajaxOptions, thrownError){ $("#content").empty().append("* Error from server cause: "+thrownError).addClass("error"); } ,
           success:function(data){$("#content").empty().append(data);}
             });

when I run the code I still receive the following error(from ajax):

  Error from server cause:Internal Servlet Error

I also tried to display the serialized object List<Gps> in the same java page without ajax, as follows:

EntityManagerFactory emf=Persistence.createEntityManagerFactory("JavaApplication21PU");
        GpsJpaController gjc=new GpsJpaController(emf);
        java.util.List<Gps> listGps=gjc.findGpsEntities();

        Gson gson=new Gson();
        String json=gson.toJson(listGps);

        System.out.println(json);

I get this Error:

Exception in thread "main" java.lang.StackOverflowError
    at java.lang.StrictMath.floorOrCeil(StrictMath.java:355)
    at java.lang.StrictMath.floor(StrictMath.java:340)
    at java.lang.Math.floor(Math.java:424)
    at sun.misc.FloatingDecimal.dtoa(FloatingDecimal.java:620)
    at sun.misc.FloatingDecimal.<init>(FloatingDecimal.java:459)
    at java.lang.Double.toString(Double.java:196)
    at java.lang.Double.toString(Double.java:633)
    at com.google.gson.stream.JsonWriter.value(JsonWriter.java:441)
    at com.google.gson.Gson$4.write(Gson.java:270)
    at com.google.gson.Gson$4.write(Gson.java:255)

Please Help!

EDIT: the final solution of this problem

score 3 · Accepted Answer · answered Apr 05 '12 at 11:05

3

StackOverflowException occurs due to infinite recursion. You may need to check the code thoroughly for any unintended recursion.

answered Apr 05 '12 at 11:05

grassyburrito

1,213
22
32

http://stackoverflow.com/questions/10036958/the-easiest-way-to-remove-the-bidirectional-recursive-relationships – Marwen Trabelsi Apr 06 '12 at 18:02

score 2 · Answer 2 · answered Apr 05 '12 at 11:07

2

Looks like your Gps objects contain references to themselves.

answered Apr 05 '12 at 11:07

ahanin

892
4
8

1

Considering that it has happened while converting to json by Gson I guess @ahanin is right. Gps might be the culprit. – grassyburrito Apr 05 '12 at 11:10

How to serialize a java.util.List to Json using Gson Library?

2 Answers2

Linked