I believe that adding support for Glassfish will help promote the adoption of Seam. In my mind, Tomcat is not nearly as important because it is not a Java EE-compliant environment and seam-gen is all about creating compliant projects.
Supporting Glassfish is actually quite straightforward. There are a couple of assumptions that are made by seam-gen that render it incompatible with a generic Java EE-compliant application server. Here is what needs to change:
1. The java:/ prefix on the data source causes problems with other servers. This can be easily brought into compliance by adding <use-java-context>false</use-java-context> to the
ds.xml files and removing the java:/ prefix from the persistence.xml files in the seam-gen/resources/META-INF directory
2. Glassfish does not use Hibernate EntityManager as the default JPA provider, and therefore does not have any of its jar files. Of course, we could just make everyone copy necessary hibernate jar files into the glassfish installation directory, but that just isn't going to go over well. I think a better approach is to modify the build.xml file to copy the following three libraries if the property hibernate.needed=true is set:
jboss-archive-browsing.jar (not currently in the seam distribution, but stuck inside the jboss-embedded-all.jar file)
3. Make the hibernate.transaction.manager_lookup_class parameterized, perhaps asking during setup
4. Removing the .war suffix on the exploded archive directory (so that Glassfish can deploy the directory using asadmin deploydir)
That's it! Then you can have Glassfish working.