How do I extract a nested JSON object using JSNI Overlay Types in GWT?

Question

So I have this JSON object coming to me which has roughly the following format:

{   "student":{"field1":"","field2":"",....},
    "subjects":[{},{},....,{}]                     }

How do I extract the entire contents of "student" and each object in the array of "subjects" in GWT using overlay types and the JsonUtils methods?

Answer 1

The easiest way is to make a JavaScriptObject that exposes the wrapper object to Java, with getters for the student and subjects properties as other JavaScriptObject and JsArray.

final class StudentAndSubjects extends JavaScriptObject {
  protected StudentAndSubjects() { }

  public native Student getStudent() /*-{ return this.student; }-*/;
  public native JsArray<Subject> getSubjects() /*-{ return this.subjects; }-*/;
}

final class Student extends JavaScriptObject {
  protected Student() { }

  public native String getField1() /*-{ return this.field1; }-*/;
  public native String getField2() /*-{ return this.field2; }-*/;
  …
}

final class Subject extends JavaScriptObject {
  protected Subject() { }

  …
}

You can then use them like this:

StudentAndSubjects sas = JsonUtils.safeEval(json);
Student student = sas.getStudent();
JsArray<Subject> subjects = sas.getSubjects();
for (int i = 0, l = subjects.length(); i < l; i++) {
  Subject subject = subjects.get(i);
  …
}