replace clunky format override with a cleaner filter

[denevers]

GSIP content negotiation can override the Accept header by passing a f= parameter using a list of well known format key (stored in the configuration). right now, it's clunky code in each handler that tests this override before invoking the code.

A cleaner way to do this is to implement a PreMarcher change the Accept header

import java.io.IOException;
import java.util.ArrayList;

import javax.ws.rs.container.ContainerRequestContext;
import javax.ws.rs.container.ContainerRequestFilter;
import javax.ws.rs.container.PreMatching;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.ext.Provider;

@Provider
@PreMatching
public class FormatRequestFilter implements ContainerRequestFilter {

	@Override
	public void filter(ContainerRequestContext requestContext) throws IOException {
		String format = requestContext.getUriInfo().getQueryParameters().getFirst("f");
		ArrayList<String> mediaTypes = new ArrayList<>();
		if ("application/json".equals(format) || "json".equals(format))
			mediaTypes.add(MediaType.APPLICATION_JSON);
		if ("text/html".equals(format) || "html".equals(format))
			mediaTypes.add(MediaType.TEXT_HTML);
		if (mediaTypes.size() > 0)
			requestContext.getHeaders().put("Accept", mediaTypes);
		
	}

}

this will override the header before routing the call to the right handler