Just ahead of this Thursday's Google Developer Day 2007 events, Google began offering on Tuesday a release candidate for Google Web Toolkit (GWT) 1.4, an upgrade to the company's framework for writing AJAX (Asynchronous JavaScript and XML) applications in Java.

Focused on improvements in speed and stability, version 1.4 features optimized output in which applications load faster. Developers can speed up existing Google Web Toolkit applications by recompiling with the 1.4 release candidate, which is downloadable here.

The toolkit is intended to make it easier to write AJAX applications such as Google Maps and Gmail. No date has been set for the general release of version 1.4

"This is undoubtedly the biggest GWT release yet," said Bruce Johnson, a developer of the toolkit, in a blog. "In addition to 150-plus bug fixes, GWT 1.4 RC includes a ton of new features, improvements, and optimizations."

An ImageBundle capability in version 1.4 creates a single composite image from many small ones, allowing for consolidation of HTTP requests. This improves application responsiveness, the company said. The composite image is permanently cacheable, which means users' time is not spent on bytes they already have, Google said.

Version 1.4 also features an enhanced UI library with widgets that make it easier to build user interfaces. A RichText widget provides a simpler way to add sophisticated text-editing capabilities to applications while a SuggestBox widget offers auto-complete functionality that can be tailored to any need, Google said.

HorizontalSplitPanel and VerticalSplitPanel capabilities enable resizing of portions of the user interface.

Benchmarking functions in the toolkit integrate with the JUnit testing framework, so developers can record and compare the speed of code snippets across different parameters. Internationalization and localization support has been improved with NumberFormat and DateTimeFormat capabilities, which allow developers to parse and format numbers, dates, and times for users worldwide, Google said.

The toolkit was launched a year ago and has been used to build products, such as Google Checkout, for online shipping. Google made the toolkit available in an open source format, via an Apache 2.0 license, later in 2006.

The company noted that the creators of the toolkit, Johnson and Joel Webber, will speak at Google Developer Day 2007, in San Jose, Calif. on Thursday. Google Developer Day events also are being held in 10 locations around the world for users of Google APIs and developer tools. Places such as Sao Paolo, Brazil; London, and Paris also will host Google developer events on Thursday.

Featured on the agenda are discussions on technologies such as Google AJAX APIs, the Google Maps, YouTube APIs, and mashups.