Thursday, January 4, 2018

Re: Problem compiling GWT code with Java9

If you aren't using java 9 modules, the latest release will work.  It does this by reading the classpath from System.getProperty("java.class.path"), so if you are using standard tools for creating classpath, everything should work fine.  If you are doing anything non-standard for assigning classpaths, or if you are using java 9 modules (i.e. you supply a modulepath instead of classpath), this will very likely not work for you.

Per my previous comments, my colleagues (Colin Alworth and Justin Hickman) and I did start a GWT-based services company,  If you want to chat, you can send an email to or come chat in  We generally help anyone for free in the public chat room, since it helps everyone to learn about fixes, but for anything requiring dedicated engineering effort, we prefer to do a support contract.

While I cannot say what the team at Google has in store for java 9 in gwt 2, I do have a prototype fix for java 9 modules on an old branch, so if you do run into trouble, feel free to post here, but you'll likely get a much faster response in gitter.  I have the jars pushed to a public-facing artifactory, and can give out coordinates if you have more exotic needs (and are willing to use coarse workarounds while a better solution is developed).  My fix resorts to reflection to access new java 9 classloader types, needs a bunch of ugly flags to open modules for reading by classloaders, and even had to unpack all of gwt-user and gwt-dev to avoid overloaded packages (no longer legal to have the same package in more than one jar in java 9).

Getting a prototype "this can work" was pretty easy, but getting it fully cleaned up with necessary modularization / refactoring is a potentially large chunk of work that could affect many files.  

So, I hope the "java.class.path" workaround works for you.  If it doesn't, come see us in gitter, or post back here (if you are ok waiting a few days for a response).

You received this message because you are subscribed to the Google Groups "GWT Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to
To post to this group, send email to
Visit this group at
For more options, visit

No comments:

Post a Comment