Implementing a JSONP interceptor in Jersey

Question

I would like to implement a JsonP interceptor, and I'm using Jersey. (I am using AsyncResponses with Long-polling, and my REST method returns 'void' therefore I can't annotate it with @JSONP)

My problem is I don't know how to get the query params. I need to know the 'callback' method name.

I also tried a regular Servlet filter. It worked, but strangely I got methodname() {my json} instead of medhodname({my json}).

So I tried the Jersey way. Seems like I need a WriterInterceptor, but how do I get the query param?

Here's my code:

@Provider
public class JsonpResponseFilter implements WriterInterceptor {

    @Override
    public void aroundWriteTo(WriterInterceptorContext context) throws IOException, WebApplicationException {
        final String callback =  (String)context.getProperty("callback");
        if (null != callback) {         
            context.getOutputStream().write((callback+"(").getBytes());
        }
        context.proceed();
        if (null != callback) {         
            context.getOutputStream().write(')');
        }
    }
}

Edit:

I found a way to get the query params, but it seems like hacking to me (see below). There's got to be something simpler or more elegant. Any ideas?

@Provider
public class JsonpResponseFilter implements WriterInterceptor {

    @Override
    public void aroundWriteTo(WriterInterceptorContext context) throws IOException, WebApplicationException {

        final ServiceLocator locator = ServiceLocatorClientProvider.getServiceLocator(context);
        ContainerRequestContext tmp = locator.getService(ContainerRequestContext.class);
        List<String> callbacks = tmp.getUriInfo().getQueryParameters().get("callback");
        String callback = (null == callbacks)? null:callbacks.get(0);
        ...

Answer 1

A less hacky solution is to inject a Provider as a field in your class:

@Inject
private Provider<ContainerRequest> containerRequestProvider;

From here, you can access the query params like this:

final ContainerRequest containerRequest = containerRequestProvider.get();
final UriInfo uriInfo = containerRequest.getUriInfo();
final MultivaluedMap<String, String> queryParameters = uriInfo.getQueryParameters();
final List<String> queryParameter = queryParameters.get("q");
...