Jersey ParamConverter exceptions not handled by ExceptionMapper - exception

Question

Per title, exceptions thrown from a ParamConverter are NOT handled the way I expect.
With an ExceptionMapper:
#Provider
public class MyExceptionMapper implements ExceptionMapper<MyException> {
#Override
public Response toResponse(MyException exception) {
return Response.serverError().entity( "It triggered" ).build();
}
}
and ParamConverter:
#Provider
(boilerplate junk)
#Override
public DateTime fromString(String value) {
throw new MyException("convert");
}
It does NOT return the "It triggered" text in a 500 error, but rather a 404.
Anticipated question : Are both providers registered?
Yes - If I throw "MyException" from a resource (within 'regular' code) it works as expected. I can also convert see the stacktrace with the "convert" message.
Is there any way to make exceptions from ParamConverters be handled by the ExceptionMapper?
I am using jersey 2.3.1, along with spring-jersey, launched in a jetty container 9.1.0.RC0

Answer 1

Seem from reading this, the JAX-RS spec says the implementor should wrap unhandled exceptions in a NotFoundException (404) for #QueryParam and #PathParam, and from what I tested a 400, (I'm guessing BadRequestException) for #FormParam.
"if the field or property is annotated with #MatrixParam, #QueryParam or #PathParam then an implementation MUST generate an instance of
NotFoundException (404 status) that wraps the thrown exception and no entity"
A couple ways I can see handling the exception, is to
Just handle it in the ParamConverter, e.g.
return new ParamConverter<T>() {
#Override
public T fromString(String string) {
try {
return (T)new MyObject().setValue(string);
} catch (MyException ex) {
Response response = Response.serverError().entity("Boo").build()
throw new WebApplicationException(response);
}
}
#Override
public String toString(T t) {
return t.toString();
}
};
Or just have your exception extend WebApplicationException, and return the Response there. e.g.
public class MyException extends WebApplicationException {
public MyException(String message) {
super(Response.serverError().entity(message).build());
}
}

Answer 2

I experienced the same behavior in Jersey 2.26.
Any Exception that extends RuntimeException gets mapped to a ParamException, which is itself a sublcass of WebApplicationException.
Assuming your MyException extends RuntimeException, it's not getting caught because your ExceptionMapper only handles MyException.
Regarding the Jersey docs saying to throw a NotFoundException: I would argue a 404 does not apply when a queryParam can't be converted. A BadRequestException seems more appropriate. And also, I can't see anything unique in the Jersey frame work when a NotFoundException is thrown besides setting the response code
To get exceptions thrown from a ParamConverter end up in an ExceptionMapper, you'll have to have your ExceptionMapper catching a more global exception, like Throwable.
Another answer suggests returning a WebApplicationException. This should be a fine solution but will NOT work if the Response object has an entity. See here: https://github.com/jersey/jersey/issues/3716