Validation does client side validation, so we need both sources.
http://gwt-code-reviews.appspot.com/1047802/diff/3001/4002 File samples/validation/build.xml (right): http://gwt-code-reviews.appspot.com/1047802/diff/3001/4002#newcode23 samples/validation/build.xml:23: <include name="javax/validation/validation-api-1.0.0.GA-sources.jar" /> It uses gwt-servlet-deps.jar, but it also needs sources because it does client side validation. http://gwt-code-reviews.appspot.com/1047802/diff/3001/4002#newcode25 samples/validation/build.xml:25: <include name="hibernate/validator/hibernate-validator-4.1.0.Final-sources.jar" /> GWT user provides super source versions of hibernate validator, which the sample uses, so we need the sources to compile. http://code.google.com/p/google-web-toolkit/source/browse/#svn/trunk/user/src/org/hibernate/validator%3Fstate%3Dclosed http://gwt-code-reviews.appspot.com/1047802/show -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
