Custom error message containing parameter names when validation fails

Question

I would like my API to return errorMessage when the request lacks of required parameters. For example let's say there is a method:

@GET
@Path("/{foo}")
public Response doSth(@PathParam("foo") String foo, @NotNull @QueryParam("bar") String bar, @NotNull @QueryParam("baz") String baz)

where @NotNull is from package javax.validation.constraints.

I wrote an exception mapper which looks like this:

@Provider
public class Mapper extends ExceptionMapper<ConstraintViolationException> {

  @Override
  public Response toResponse(ConstraintViolationException) {
    Iterator<ConstraintViolation<?>> it= exception.getConstraintViolations().iterator();
    StringBuilder sb = new StringBuilder();
    while(it.hasNext()) {
      ConstraintViolation<?> next = it.next();
      sb.append(next.getPropertyPath().toString()).append(" is null");
    }
    // create errorMessage entity and return it with apropriate status
  }

but next.getPropertyPath().toString() returns string in format method_name.arg_no, f.e. fooBar.arg1 is null

I'd like to receive output fooBar.baz is null or simply baz is null.

My solution was to include -parameters parameter for javac but to no avail.

Probably I could somehow achieve it with the use of filters:

public class Filter implements ContainerResponseFilter {

@Override
public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext) {

    UriInfo uriInfo = requestContext.getUriInfo();
    UriRoutingContext routingContext = (UriRoutingContext) uriInfo;

    Throwable mappedThrowable = routingContext.getMappedThrowable();

    if (mappedThrowable != null) {
        Method resourceMethod = routingContext.getResourceMethod();
        Parameter[] parameters = resourceMethod.getParameters();

      // somehow transfer these parameters to exceptionMapper (?)
    }
  }
}

The only problem with the above idea is that ExeptionMapper is executed first, then the filter is executed. Also I have no idea how could I possibly transfer errorMessage between ExceptionMapper and Filter. Maybe there is another way?

Answer 1

You can inject ResourceInfo into the exception mapper to get the resource method.

@Provider
public class Mapper extends ExceptionMapper<ConstraintViolationException> {

    @Context
    private ResourceInfo resourceInfo;

    @Override
    public Response toResponse(ConstraintViolationException ex) {
        Method resourceMethod = resourceInfo.getResourceMethod();
        Parameter[] parameters = resourceMethod.getParameters();
    }
}