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GSON on Google App Engine throws a Security Exception

Answer 1

A:

If App Engine does not support Reflection, then we are pretty much left to write our own toJSON method. This can be done as follows (not a big deal but someone might find it useful):

public SampleObject {

  //...

  /**
   * Convert this object to a JSON object for representation
   */
  public JSONObject toJSON() {
    try {
       JSONObject jsonobj = new JSONObject();
       jsonobj.put("id", this.id);
       jsonobj.put("name", this.name);
       return jsonobj;
    } catch(Exception e) {
       return null;
    }
  }
}

Then, you can use a toString method on this object to print out the JSON representation. Not the best I agree but some workaround for now.

Legend 2010-06-09 03:12:44

Answer 2

+2 A:

The app engine does support reflection - however you are trying to reflect on a private field of a JRE class:

Reflection

An application is allowed full, unrestricted, reflective access to its own classes. It may query any private members, use java.lang.reflect.AccessibleObject.setAccessible(), and read/set private members.

An application can also also reflect on JRE and API classes, such as java.lang.String and javax.servlet.http.HttpServletRequest. However, it can only access public members of these classes, not protected or private.

An application cannot reflect against any other classes not belonging to itself, and it can not use the setAccessible() method to circumvent these restrictions.

...from http://code.google.com/appengine/docs/java/runtime.html#The_Sandbox:

I'd consider writing a custom serializer for Bitset.

See: http://sites.google.com/site/gson/gson-user-guide#TOC-Custom-Serialization-and-Deserializ

Also: http://groups.google.com/group/google-gson/browse_thread/thread/535892ffcf691aa/897f27e37e03ce58?lnk=gst&q=bitset#897f27e37e03ce58

http://groups.google.com/group/google-gson/browse_thread/thread/535892ffcf691aa

Ash Kim 2010-06-09 15:01:25

@Ash: Thank You. I guess in my case, I am not sure why GSON is doing what it is doing :) If you know of any other ways of getting it work, it would be awesome.

Legend 2010-06-09 23:22:06

No wukkas. Perhaps regisiter a custom serializer for Bitset?

Ash Kim 2010-06-10 03:30:55

@Ash: Thanks for the suggestion. I will look into it.

Legend 2010-06-10 19:39:10

Answer 3

A:

You can construct GsonBuilder with .excludeFieldsWithoutExposeAnnotation(), and mark all serialized fields with @Expose annotation. In this case, Gson doesn't try to serialize fields other that you want.

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.excludeFieldsWithoutExposeAnnotation();
String json = gsonBuilder.create().toJson(modelObject);

Vasiliy 2010-08-12 09:24:49

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GSON on Google App Engine throws a Security Exception

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