Required @QueryParam in JAX-RS (and what to do in their absence)

Question

I deploy a web-services component to JBoss Application Server 7 using the RESTEasy JAX-RS implementation.

Is there an annotation available to declare required, mandatory @QueryParam parameters in JAX-RS ? And, if not, what is the 'standard' way to deal with situations where such parameters are missing?

My web service (resource) methods return JSON-stringified results when properly invoked with all the mandatory arguments, but I'm not sure what is the best way to indicate to the caller that a required parameter was missing.

Answer 1

Good question. Unfortunately (or maybe fortunately) there is no mechanism in JAX-RS to make any params mandatory. If a parameter is not supplied it's value will be NULL and your resource should deal with it accordingly. I would recommend to use WebApplicationException to inform your users:

@GET @Path("/some-path") public String read(@QueryParam("name") String name) {   if (name == null) {     throw new WebApplicationException(       Response.status(Response.Status.BAD_REQUEST)         .entity("name parameter is mandatory")         .build()     );   }   // continue with a normal flow } 

Answer 2

You can use javax.validation annotations to enforce that the parameters are mandatory by annotating them with @javax.validation.constraints.NotNull. See an example for Jersey and one for RESTeasy.

So your method would simply become:

@GET @Path("/some-path") public String read(@NotNull @QueryParam("name") String name) {   String something =    // implementation   return something; } 

Note that the exception gets then translated by the JAX-RS provider to some error code. It can usually be overridden by registering your own implementation of javax.ws.rs.ext.ExceptionMapper<javax.validation.ValidationException>.

This provides a centralized way to translate mandatory parameter to error responses and no code duplication is necessary.