As part of our design and development for our Thin-Client annotation tool, we decided to combine the Google Web Toolkit (GWT) and Flex as the main implementation technologies. GWT is a relatively new set of open source tools that allows you to create and maintain front-end JavaScript applications in Java. This means that the front end code is written in Java that is compiled by GWT into optimized JavaScript that works across all major browsers. Eliminating handwritten JavaScript can greatly simplify front-end coding. However, if the application needs to do something that GWT cannot, JavaScript can be inserted straight into the Java program. A number of widget libraries are available from Google and third parties but if none suit a specific needs (as was the case with our sticky notes); it is quite simple to create a custom widget.

Another advantage of GWT is that it allows debugging in a hosted mode browser, so most changes in the client side code can be viewed by simply refreshing the browser. Several plug-ins are available which allow GWT development in different development environments including Eclipse.

GWT’s layout concept can be the main learning curve for developers unfamiliar with GWT.  Most of the page layout is based on the placement of horizontal and vertical panels. All widgets in a horizontal panel will appear on the page lined up horizontally. If the user wants one of the widgets to be below the rest, that widget will need to be placed in a vertical panel with the previously mentioned horizontal panel. Once the layout concept is grasped, it quickly becomes quite intuitive but it was frustrating at first. The only other issues we ran into came from the fact that GWT does so much internally (JavaScript compiling, RPC calls, etc), this can make debugging more difficult since it can be hard to identify what the actual root of a problem is.

Overall, GWT was a great tool for front-end JAVA development. It eliminated a lot of time that would have to be devoted to JavaScript development. There are some really helpful tutorials on the Google Code website (http://code.google.com/webtoolkit/tutorials/1.6/index.html ) for anyone interested in learning more about development in GWT.

Here is a screenshot of our GWT Annotation tool interface. Be sure to check back often as we will be releasing our annotation demo shortly.