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First I must admit that I don't buy GWT's approach. There is a reason why we don't write HTML code from servlets anymore. Programmers usually are bad UI designers (look at my website for something to back my claim ;-) and great UI designers usually don't want to write Java code. With the GWT model you write your UI in Java and automatically translate it to HTML. This means layout changes require the Java coder to perform it, which is bad. Maybe you can get around most problems with the help of CSS, but I doubt that.

Anyway, I downloaded the toolkit and played with it last night, and found it to be a bit cumbersome to work with. Scripts that generate scripts and no integration with Ant to speak of.

I stopped after my first few steps and started to put together a little Ant library that makes using GWT a bit less cumbersome - at least to me. This is very rough alpha level code, but it works for me. I'm not sure I'll take this any further, but if anybody is interested in it, feel free to use the code - the license is pretty permissive. Source and binaries are available here.

There is no documentation right now. A quick rundown:

• This is an Ant library which means you need Ant 1.6.0 or better. It lives in the antlib:de.samaflost.gwttasks namespace by default.
• Throughout the rest of this blog entry I'll assume you have something like xmlns:gwt="antlib:de.samaflost.gwttasks" on your <project> tag.
• All tasks have a mandatory gwtHome attribute that points to your GWT installation.
• gwt:projectCreator is almost as pointless as the corresponding script. The major difference is that it doesn't create any Eclipse stuff and that the generated Ant build file is a tiny bit cleaner. Don't use this task. 8-)
• gwt:applicationCreator is similar to the corresponding script but creates an Ant build file which includes the compile, clean and package targets projectCreator would have created but also contains a bunch of additional targets leveraging the other tasks.

  This task has an optional dir attribute pointing to the directory that you want to hold your GWT project structure and a mandatory className attribute (corresponding to the className argument the applicationCreator script of GWT requires).

  There also is an optional boolean attribute that controls the -eclipse command line argument of the applicationCreator script that is called under the covers.

  The outDir is only used while writing the build file, it provides the value for the next two tasks' outDir attributes and defaults to "www"./p>

  Finally there is a template attribute that can be used to point to a build file template if you don't like the one created by this task. The token @PROJECT@ will be replaced by the last part of the className attribute, @GWT_HOME@ will point to gwtHome, @CLASS_BASE@ is className without ".client" and @OUT@ is the outDir attribute.

• gwt:compile runs the Java -> JavaScript compiler.

  The outDir and classBase attributes make up the output directory - in the script generated by the applicationCreator script they are "www" and className without ".client" repectively.

  There is an optional dir attribute if your GWT application's src directory is not directly below your basedir.

• gwt:shell starts the GWT shell and takes the same arguments as the compile task - only classBase is replaced by startPage which is built by appending the unqualified class name to what would be compile's classBase plus a slash and adding an ".html" extension.

Reading this a second time, it is a bit confusing, I guess.

You must provide a class name to Google's applicationCreator script, let's say you've chosen de.samaflost.client.Dummy (the .client. piece is recommended by Google), then gwt:compile's classBase would be de.samaflost.Dummy and 's startPage would be de.samaflost.Dummy/Dummy.html.

Putting the stuff together. To seed a new GWT application you'd use

  <target name="applicationCreate">
    <mkdir dir="project"/>
    <gwt:applicationCreator dir="project"
      gwtHome="C:/OSS/gwt-windows-1.0.20/"
      className="de.samaflost.client.Dummy"/>
  </target>

This will generate the initial directory structure in the project subdirectory and will also generate an Ant build file that contains (among other things)

  <target name="gwt-compile" depends="compile">
    <gwt:compile outDir="www" gwtHome="C:\OSS\gwt-windows-1.0.20"
      classBase="de.samaflost.Dummy"/>
  </target>

  <target name="gwt-shell" depends="compile">
    <gwt:shell outDir="www" gwtHome="C:\OSS\gwt-windows-1.0.20"
      startPage="de.samaflost.Dummy/Dummy.html"/>
  </target>

This means you don't need to worry about classBase or startPage at all. It also means you now have the Java -> JavaScript step as part of your Ant build process and available to your continuous integration runs.

I haven't found the time for an actual RPC example yet, but expect it will lead me to a special gwt:war task that knows what to package where.

Finally, it may be worth noting that three of the four tasks are implemented in Ant, not Java (i.e. they are <macrodef>'s hidden in the antlib descriptor.

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• Java
• GWT