If you don't use Mac OS X 10.6 (Snow Leopard), the GWT 1.7.1 release shouldn't interest you much -- you shouldn't see any changes. If you do use Mac OS X 10.6, good news. Running GWT with Java 6 has become simpler. Download it here.
GWT's hosted mode uses the Standard Widget Toolkit (SWT), which only supports 32-bit operation. Hosted mode must therefore also run a 32-bit version of Java. Mac OS X 10.5 (Leopard) shipped with a 32-bit Java 5 and a 64-bit only Java 6. Java 5 was compatible with the 32-bit SWT bindings, so the GWT SDK directed users to use Java 5 only. With the Snow Leopard release, Apple only includes Java 6, but it now runs in both 32-bit and 64-bit modes.
In short, you can now run GWT on Snow Leopard using the Java command line argument -d32 without further modification. The GWT SDK no longer directs you to only use Java 5, and the ant scripts (including scripts generated by the webAppCreator tool) have been updated to include the -d32 flag where necessary. Also, Linux users will see a more informative error message when a non-32-bit Java runtime is used..
