In GWT, what does the "[...].java' is removed due to invalid reference(s)" mean?

Question

I have converted a GWT Eclipse based project to GWT-Maven but when I run the command

mvn clean gwt:compile

I get an awful lot of errors that specify:

[class name].java' is removed due to invalid reference(s):

My pom.xml dependencies are:

• dom4j-1.6.1
• commons-httpclient-3.1
• gwt-servlet-1.6.4
• gwt-user-1.6.4
• junit-4.3.1
• gwtext-2.0.5
• GWTx-20070605

What do these errors mean and how do I go about diagnosing the source of the problem?

Answer 1

That's because the removed class refers to a method that is implemented as part of the GWT JRE emulation library :

http://library.igcar.gov.in/readit2007/tutori/tools/gwt-windows-1.4.10/doc/html/jre.html

If your software makes use of reflection it is very probably the cause.

Answer 2

Typically this means that something higher up in the calling chain was invalid, either because of a compile error, or because it was, or was using, a class that can't be 'compiled' by the GWT compiler. So, if you have class A which references class B, and class B cannot be compiled, class A will be removed due to an invalid reference.