GWT Deobfuscator Builder ClassCastException - gwt

Question

I have a GWT webapp which uses a RequestFactory - the app seems to launch just fine, but as soon as I try to open it in a browser, it blows up with this exception:
com.google.web.bindery.requestfactory.server.RequestFactoryServlet doPost
SEVERE: Unexpected error
java.lang.ClassCastException: class com.myapp.console.shared.MyAppRequestFactoryDeobfuscatorBuilder
at java.lang.Class.asSubclass(Class.java:3126)
at com.google.web.bindery.requestfactory.vm.impl.Deobfuscator$Builder.load(Deobfuscator.java:52)
at com.google.web.bindery.requestfactory.server.ResolverServiceLayer.updateDeobfuscator(ResolverServiceLayer.java:43)
at com.google.web.bindery.requestfactory.server.ResolverServiceLayer.resolveRequestFactory(ResolverServiceLayer.java:176)
at com.google.web.bindery.requestfactory.server.ServiceLayerDecorator.resolveRequestFactory(ServiceLayerDecorator.java:172)
at com.google.web.bindery.requestfactory.server.ServiceLayerDecorator.resolveRequestFactory(ServiceLayerDecorator.java:172)
at com.google.web.bindery.requestfactory.server.ServiceLayerDecorator.resolveRequestFactory(ServiceLayerDecorator.java:172)
at com.google.web.bindery.requestfactory.server.ServiceLayerDecorator.resolveRequestFactory(ServiceLayerDecorator.java:172)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.web.bindery.requestfactory.server.ServiceLayerCache.getOrCache(ServiceLayerCache.java:233)
at com.google.web.bindery.requestfactory.server.ServiceLayerCache.resolveRequestFactory(ServiceLayerCache.java:198)
at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:215)
at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:135)
at com.google.web.bindery.requestfactory.server.RequestFactoryServlet.doPost(RequestFactoryServlet.java:133)
....
The MyAppRequestFactoryDeobfuscatorBuilder class is auto-generated (my class is MyAppRequestFactory), so it's proving very difficult to debug. This didn't used to happen a few weeks ago when I last used this app. What's causing this error and how do I fix it? I'm not a GWT expert, so small words and understandable explanations would be appreciated!

Answer 1

This is likely a classloader issue, Deobfuscator.Builder being loaded from a different (and sibling or child, not parent) classloader than MyAppRequestFactoryDeobfuscatorBuilder, so the Deobfuscator.Builder parent class of MyAppRequestFactoryDeobfuscatorBuilder is not the same as the Deobfuscator.Builder class that tries to load it.
Did you change anything between the time it worked and now?
(note: GWT 2.6.0's DevMode has a classloader issue, so if you updated to GWT 2.6.0 and don't strictly follow the expected project layout –i.e. some libs missing from your WEB-INF/lib and/or your compiled classes not being in WEB-INF/classes– then you could run on such issue)