Saturday 9 June 2007

GWT and Maven 2, OH the pain!

GWT - Maven2 and Eclipse .. Ouch!

Using GWT for all of 3 weeks now, I am finding it is nice. It's logical, well thought out and simple.

But, I think there is a little way to go when it comes to using some de jure standards. I am a big Maven 2 fan because in an Enterprise (captial E for 'ooh' fancy) environment, standards go a LONG way and Maven 2 dictates a nice and well understood way of doing things.

So, what's me beef with GWT ? Simply this, gosh it has been hard to get it working with Maven 2.

Now, part of this is because I am still trying to get my head around how it works. I have been using the applicationCreator script to setup a quick hello world sample, then move that into the src/main/java and src/main/resources folders.
But what does that do to my src/main/webapp ? where do the images get pulled from ? why don't index.jsp load in the GWTShell (when it's tomcat underneath) ? So many questions.

So, there is a maven 2 plugin. I am currently using the 1.5.2 version of it.

Google Code Homepage :
Maven 2 Plugin Doc :
A list of some problems :
Maven Repo :
SVN Repository :

and as it turns out, there are a few bugs and features which need some work. (I wish I saw that FAQ page first before diving in)

The first issue I cam across was the "plural" vs "singular" naming convention. In Maven 2, a configuration item for a plugin that requires more than one value is pluralised .. ie



What's the problem ?

Well, the com.totsp.gwt plugin needs a configuration line like


However, this config value in the plugin source needs an [] array or targets. (logical yes) but m2 plugins, dictate that the property name is then plural (compileTargets) otherwise you get this kind of error message.

[INFO] Failed to configure plugin parameters for: com.totsp.gwt:maven-googlewebtoolkit2-plugin:1.5.3-SNAPSHOT

(found static expression: 'org.sobbo.ui.client.Home' which may act as a default value).

Cause: Cannot assign configuration entry 'compileTarget' to 'class [Ljava.lang.String;' from 'org.sobbo.ui.client.Home', which is of type class java.lang.String

so .. the AbstractGWTMojo has to change to have a plural of configurationTargets (there must be a way else how would they be using it right now ?

It turns out there is an issue logged for this ..

Anyways, what's the next pain ? well to checkout the src from the subversion repository, you get this nice little gem.

$ svn co

svn: REPORT request failed on '/svn/!svn/vcc/default'
svn: REPORT of '/svn/!svn/vcc/default': 400 Bad Request (

BANG, and there is my pain. This looks like a straight up Google SVN problem. Funny enough, I have an SVN downloaded script that works to "download" src from SVN repositories using wget.

See the end of this post for the shell script.

So .. my third issue ? Well there was some unusual "Java Execution Mojo Bootstrapping" stuff going on, and it's broken. Essentially when trying to launch java to compile (testing, shell etc) it (the GWT maven plugin) couldn't find it (java) and died. I found the problem (after downloading the src and corrected it) and logged this issue with a patch @ GWT M2 Plugin Issue 43

So .. is it ready ? This Maven 2 plugin really needs to be working, maven 2 is big and GWT / M2 / Spring / Eclipse is pretty important (to me at least).

I'll keep battling with it because this way I can probably make it a little better. I hope that it gets better.

So, that SVN downloader script, it's not completely "safe" because the revision could change by a third party part way through your download, but hey, it works.
# Author: Ramon Buckland
# Quick hack script to pull the latest SVN Revision version from a repo repo when you have no SVN tools
# or SVN through ISA proxy servers are just not working ..

function usage {
echo "$0 "
echo "svn-url: SVN URL is a URL to the trunk or a tag you interested in"
echo " eg:"
echo "product-name: A short name of the product so that we can create a directory for you"
echo " eg: servicemix"
echo "(also, set the http_proxy=http://hostrunning-ntlmaps:port)"

if [ "X$1" == 'X' ]; then

if [ "X$2" == 'X' ]; then

if [ "X$http_proxy" == 'X' ]; then
echo "WARNING: http_proxy is not set. Do you need it ?"


mkdir ${PRODUCT_NAME}-svn-pid-$$
cd ${PRODUCT_NAME}-svn-pid-$$

# nv=non-verbose
# nH=noHost directory created
# -np=no ascend to paremt dirs
# --cut-dirs=3
# -erobots=off .. don't look at robots.txt to see what you are and aren't allowed to do
# -m mirror

wget -nv -nH -np --cut-dirs=3 -erobots=off -m ${SVN_REPO}

NEWDIR=`grep Revision index.html | grep h2 | cut -d':' -f1 | cut -d'>' -f2 | tr ' ' _`
cd ..
mv ${PRODUCT_NAME}-svn-pid-$$ ${PRODUCT_NAME}-svn-${NEWDIR}
find . -type f -name index.html | xargs rm

Hope that helps someone. I use it a bit here and there.


ahhughes said...

Hi Ramon - Good postings! I'm in a very similar position to you. I would like to get GWT + Maven + Eclipse integrated. I've followed all the doco I can find. It would be great to see a settings.xml, and pom.xml because I can't figure this one out. I'm in #gwt on freenode if you use IRC.

Stefan Siprell said...

Hi Ramon,
I am totally with you, that GWT seems to be a great technology. I am quite astonished finding out, that I am not the only person having issues integrating GWT with Maven. I would have thought that every good developer would be using maven for java projects with more than 5 classes. Have you stumbled across something similiar to my problem:
Issue 63 (Just reported the issue)
Thanks again for the blog entry!

Humberto said...

I am going thru the same issues. I really believe in GWT and Maven2. But I have been having a hard time.

Unknown said...

I just knocked down another one - putting the google.webtoolkit.extrajvmargs value of "-XstartOnFirstThread"
in the settings.xml causes the gwt:compile goal to fail miserably. Remove it and the goal runs fine!
Actual error is:

[INFO] [gwt:compile]
[FATAL_ERROR] Maven Embedder execution error: org.codehaus.plexus.util.cli.CommandLineUtils.translateCommandline(Ljava/lang/String;)[Ljava/lang/String;

Unknown said...

We had a lot of difficulty getting GWT working with Maven correctly, and found the gwt-maven plugin difficult to use.

Netbeans, on the other hand has a great plugin that is very easy to use, but doesn't integrate with maven.

We build our own maven plugin that takes a similar approach to netbeans. We also included an archetype to jumpstart your application. Check it out here:

Current 5 booksmarks @