You need to create the public folder at the same level as the module configuration file <module_name>.gwt.xml . I.e:
+src/main/resources |-<module_name>.gwt.xml |-+public |-<static resources>
Thus, after compiling gwt, all resources will go to src/main/webapp/<module_name>/ . This folder is the one that maven (through the plugin), or you (manually) will use to create the final webapp.
Hope this helps.
Relations
source share