Register the StringParamUnmarshaller interface
The setAnnotations() method is called by resteasy to initialize the unmarshaller. package org.jboss.resteasy.spi; public interface StringParameterUnmarshaller { void setAnnotations(Annotation[] annotations); T fromString(String str); } You can add this by creating and registering a provider that implements this interface. You can also bind them using a meta-annotation called org.jboss.resteasy.annotationsStringParameterUnmarshallerBinder.