STEP: Create Dynamic Web Project with JAX-RS Support STEP: Create class ParamConverterProvider @Provider public class Converter implements ParamConverterProvider { @Override public <T> ParamConverter<T> getConverter( Class <T> arg0, Type arg1, Annotation[] arg2) { // TODO Auto-generated method stub return null ; } } STEP: Change return value to new ParamConverter<T>() { } @Provider public class Converter implements ParamConverterProvider { @Override public <T> ParamConverter<T> getConverter( Class <T> arg0, Type arg1, Annotation[] arg2) { // TODO Auto-generated method stub return new ParamConverter<T>() { }; } } STEP: Use quick fix "Add unimplemented methods" ASSERT: No error in Error log FAIL: There is an error "org.eclipse.jdt.internal.core.TypeParameter cannot be cast to org.eclipse.jdt.core.IType" org.jboss.tools.common Error Mon Jun 30 12:28:44 CEST 2014 org.eclipse.jdt.internal.core.TypeParameter cannot be cast to org.eclipse.jdt.core.IType org.jboss.tools.common.validation.JBTValidationException: org.eclipse.jdt.internal.core.TypeParameter cannot be cast to org.eclipse.jdt.core.IType at org.jboss.tools.common.validation.AsYouTypeValidatorManager.validate(AsYouTypeValidatorManager.java:187) at org.jboss.tools.common.validation.AsYouTypeValidatorManager.validateString(AsYouTypeValidatorManager.java:205) at org.jboss.tools.common.validation.AsYouTypeValidatorManager.validateString(AsYouTypeValidatorManager.java:200) at org.jboss.tools.common.validation.java.JavaDirtyRegionProcessor.endProcessing(JavaDirtyRegionProcessor.java:498) at org.eclipse.wst.sse.ui.internal.reconcile.DirtyRegionProcessor$BackgroundThread.run(DirtyRegionProcessor.java:697) Caused by: java.lang.ClassCastException: org.eclipse.jdt.internal.core.TypeParameter cannot be cast to org.eclipse.jdt.core.IType at org.jboss.tools.ws.jaxrs.core.jdt.SourceType.from(SourceType.java:79) at org.jboss.tools.ws.jaxrs.core.jdt.JdtUtils.getReturnType(JdtUtils.java:1143) at org.jboss.tools.ws.jaxrs.core.jdt.JdtUtils.resolveMethodSignature(JdtUtils.java:1067) at org.jboss.tools.ws.jaxrs.core.jdt.JdtUtils.resolveMethodSignatures(JdtUtils.java:1037) at org.jboss.tools.ws.jaxrs.core.jdt.CompilationUnitsRepository.recordAST(CompilationUnitsRepository.java:112) at org.jboss.tools.ws.jaxrs.core.jdt.CompilationUnitsRepository.getAST(CompilationUnitsRepository.java:76) at org.jboss.tools.ws.jaxrs.ui.internal.validation.JaxrsMetamodelValidator.validate(JaxrsMetamodelValidator.java:413) at org.jboss.tools.common.validation.AsYouTypeValidatorManager.validate(AsYouTypeValidatorManager.java:183) ... 4 more