jamesharr edited this page May 9, 2011 · 14 revisions


JSON-DTO is a GWT library for pickling objects into JSON data as well as providing an RPC mechanism very similar to GWT-RPC. It can be used to model existing JSON structures as Java objects to ease interfacing with current services. It can also be used to build new services and model the [JSON] API after Java objects in a way that’s cross-compatible with multiple client and/or browser implementations.

What JSON-DTO will do

  • Help you avoid tedious JSON parsing via GWT’s Java API.
  • Avoid hassles of GWT’s JavaScriptObjects:
    • Catch mis-formed JSON while parsing.
    • Easily see data structures from a debugger.
    • Support for more sophisticated data types and structures.
  • JSON-RPC services. This will look and feel very similar to GWT-RPC.
  • Self-referential classes. You can build linked lists or, but don’t build anything with a cycle. This will confused the pickler and send it on a recursion death-spiral. Support for this will probably never happen since the JSON mapping is not one-to-one.

What JSON-DTO won’t do

  • Polymorphism. If you say you’re pickling a Foo, you’re pickling whatever you gave us as a Foo even if it’s a FooSubClass.
  • Object graphs with cycles (see last bullet on what JSON-DTO will do).
  • Pickle private fields. Sorry, this is a GWT+Java limitation. Use default/protected/public field access.
  • There’s currently no plans to support the pickler using getter/setter methods. You can have them, but the pickler is going straight for your data.

Supported data types

  • Primitive types (and their boxed counterparts)
  • Array – Multi-dimensional
  • Parameterized Generics (keep reading).
  • Lists. Currently uses LinkedList for the implementation. ArrayList support (and possibly others) is planned.
  • Maps. Keys must be Strings currently, values can be any picklable type. Currently uses TreeSet for implementation.
  • Sets. Currently uses TreeSet for the implementation.

Example code snippets.

Bug me about this and I’ll spit out a few easily digestible samples. Until then, check out the unit tests:

Other slick stuff

I threw in some field annotations to make dealing with corner-cases and API version differences a little easier as well.

  • @Optional – Leave a field as-is if the JSON field isn’t there. Use this with a Map field in an object.
  • @IgnoreNull – If the data in an object is present, but is null, don’t set the field to null.

When running in GWT’s dev mode, I think I’m going to include support for proxying JSON-RPC calls through Jetty to avoid problems with cross-domain requests.


When will this be ready? Not entirely sure. Most of the pickling code is written, functional, and passes the tests (the tests that I’ve thought of anyway). I prototyped the project December 2010 and picked it back up April 2011. Since then I’ve made a lot of progress. If personal interest and a little bit of luck is on my side, a beta will be out mid-summer 2011.

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