GWT supports a subset of JSR 303 Bean Validation. At compile time GWT validation uses the same Validation Provider you use on the server to create a Validator for all your objects.

Building any large scale application has its hurdles, and GWT apps are no exception. Multiple developers working simultaneously on the same code base, while maintaining legacy features and functionality, can quickly turn into messy code. To help sort things out we introduce design patterns to create compartmentalized areas of responsibility within our project.
There are various design patterns to choose from; Presentation-abstraction-control, Model-view-controller, Model-view-presenter, etc... And while each pattern has its benefits, we have found that a Model-view-presenter (MVP) architecture works best when developing GWT apps for two main reasons. First the MVP model, much like other design patterns, decouples development in a way that allows multiple developers to work simultaneously. Secondly, this model allows us to minimize our use of GWTTestCase and, for the bulk of our code, write lightweight (and fast) JRE tests.