GWT multi-module project and development mode

David Vree

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Dec 9, 2011, 11:44:38 AM12/9/11

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My team is currently converting a web-app to GWT and we would like to break our client code into at least 2 and maybe as many as 4 separate Maven modules/projects.

When doing this is it possible to use development mode and allow hot code editing of the dependent modules?

Google provided me with the following links, but they seem to be inconclusive.

http://groups.google.com/group/codehaus-mojo-gwt-maven-plugin-users/browse_thread/thread/8d073905c5ec2663
http://stackoverflow.com/questions/5236181/how-to-be-productive-in-a-gwt-maven-multi-module-project
http://jira.codehaus.org/browse/MGWT-76

I am hoping somebody already does this and can provide some useful tips.

Thomas Broyer

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Dec 9, 2011, 2:59:45 PM12/9/11

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On Friday, December 9, 2011 5:44:38 PM UTC+1, David Vree wrote:

My team is currently converting a web-app to GWT and we would like to break our client code into at least 2 and maybe as many as 4 separate Maven modules/projects.

When doing this is it possible to use development mode and allow hot code editing of the dependent modules?

Yes, absolutely. Not sure you can do it in a "Maven way" though (it looks to me like Maven is not designed for such things; not that you cannot do it, but it'll be a bit "hackish")

Google provided me with the following links, but they seem to be inconclusive.

http://groups.google.com/group/codehaus-mojo-gwt-maven-plugin-users/browse_thread/thread/8d073905c5ec2663
http://stackoverflow.com/questions/5236181/how-to-be-productive-in-a-gwt-maven-multi-module-project
http://jira.codehaus.org/browse/MGWT-76

I am hoping somebody already does this and can provide some useful tips.

We're using Eclipse with m2e and the Google Plugin for Eclipse, and, in addition to "resolving artifacts from the workspace", we just add each project's source so the Eclipse launcher's classpath (yes, it has to be done manually, but you can easily share the .launcher file between computers, at least as a template).

If you also have server-side classes in your modules, it becomes much more trickier: I don't think there's another solution than running an external servlet container, point it to your packaging=war project's target/<final-name>, and add the other projects' target/classes to the webapp extra-classpath. We have a *-context.xml file for Jetty 7 that does just that; something like:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">

<Set name="contextPath">/myapp</Set>

<Arg>

<Item><SystemProperty name="project.root"/>/project-webapp/src/main/webapp/</Item>

<Item><SystemProperty name="project.root"/>/project-webapp/target/project-webapp-${project.version}/</Item>

</Array>

</Arg>

</New>

</Set>

<Set name="copyWebDir">false</Set>

<Set name="copyWebInf">false</Set>

<Set name="extractWAR">false</Set>

<Set name="defaultsDescriptor"><Property default="." name="jetty.home"/>/etc/webdefault.xml</Set>

<Set name="extraClasspath"><SystemProperty name="project.root"/>/project-webapp/target/classes/;<SystemProperty name="project.root"/>/project-module1/target/classes/;<SystemProperty name="project.root"/>/project-module2/target/classes/</Set>

</Configure>

And you launch your Jetty with -Dproject.root="" pointing to the location of your maven parent folder (where all your modules live) and -Dproject.version="" with your project's version (unless you configured the final name of the project-webapp to *not* include the version).

Eclipse will compile your java files into each project's target/classes, which are in the extraClasspath of the webapp (just like if there were in the webapp's WEB-INF/classes, or a JAR in WEb-INF/lib). To refresh the server-side code, simply "touch" the context file and Jetty will reload it (we setup Jetty to check for changes every second when developping; this is done through a Maven profile in another project which packages everything together, including some Jetty configuration files; but if you don't need such things, just change the file manually in Jetty's configuration, on each developer's computer)

This is our setup for development and it works pretty well, for almost a year now (we previously tried Eclipse WTP but had issues with it: it sometimes failed to deploy some classes, or even JARs)

In a few words: it requires a bit of time to setup everything in the beginning, but then all you have to do is: launch your local Jetty, launch the DevMode in "-noserver" from Eclipse. To debug the server-side code, make sure you launch Jetty with the debug agent (you just have to uncomment a line in the default start.ini file), and then connect to it from Eclipse as if it's a "remote app".

David Vree

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Dec 11, 2011, 12:18:24 PM12/11/11

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Thanks for the great answer. With this final issue out of the way, I am ready to have my company jump into GWT with both feet!

Even though we are a big Maven shop, I 100% agree that short-cycle rapid-development is an arena of the IDE, and not your build tool. That said, we do make extensive use of Cargo to launch our own Jetty and Tomcat instances so that we can rapidly code-test-debug on the server side. When we were doing Flex development, we would have the Flex Builder configured to drop the SWF/SWC files in the exploded WAR directory of these locally running servlet containers. Sounds like we could do the same with GPE.

The key part that I was missing was adding the source directories to the classpath in the launcher. The Google web application launcher documentation is rather sparse:

http://code.google.com/eclipse/docs/running_and_debugging_2_0.html

Whats a good resource to get schooled on this thing?

Raphael André Bauer

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Dec 12, 2011, 1:47:54 AM12/12/11

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Hi David,

I did several projects with GWT on a "larger" Maven setup involving
10+ people. Some time a go a wrote about it at:
http://ars-codia.raphaelbauer.com/2011/01/gwt-project-layout-part-2-large.html

Maven and GWT is really stable and usable, and you can do all stuff
like hot code swapping / debugging and so on once it's properly
configured.

I am 100% sure that Maven is a great tool to speed up things. But with
my experience now I am not 100% sure if it is clever having "many"
modules to split things up.

In my current projects I am trying to use as less Maven and GWT
modules as possible. Makes management of the project nicer and
simpler. If you really need more GWT / maven modules you can always do
that - but don't do stuff too complex at the beginning - premature
optimization is the root of all evil...

Another tip for large projects: Maven and a multi module setup might
be important - but it is imho more important having a working DVCS
setup - especially if you are working with many teams (I also wrote
about that at http://ars-codia.raphaelbauer.com/2011/01/git-branching-workflow.html
/ http://ars-codia.raphaelbauer.com/2011/07/mercurial-branching-workflow.html
.

Hope that helps - feedback much appreciated :)

Best,

Raphael

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David Vree

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Dec 12, 2011, 9:41:52 AM12/12/11

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@ra -- thank for the info, your article was very helpful...can't believe I didn't find it earlier....

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