[jaxrs-dev] HeaderDelegate

[Niklas Mehner <niklas.mehner@xxxxxxxxx>]

Hi,

I have a question regarding the header classes (CacheControl, EntityTag, ...) in JAX-RS. They all implement the pattern of having a static reference:

private static final HeaderDelegate<EntityTag> HEADER_DELEGATE =
        RuntimeDelegate.getInstance().createHeaderDelegate(EntityTag.class);

and implementing valueOf/toString methods:

public static EntityTag valueOf(final String value) {
    return HEADER_DELEGATE.fromString(value);
}

public String toString() {
    return HEADER_DELEGATE.toString(this);
}

What is this actually for?

RestEasy implements adding a header in org.jboss.resteasy.plugins.server.servlet.HttpServletResponseHeaders:

protected void addResponseHeader(String key, Object value)
{
   if (value == null)
   {
      return;
   }
   RuntimeDelegate.HeaderDelegate delegate = factory.getHeaderDelegate(value.getClass());
   if (delegate != null)
   {
      //System.out.println("addResponseHeader: " + key + " " + delegate.toString(value));
      response.addHeader(key, delegate.toString(value));
   }
   else
   {
      //System.out.println("addResponseHeader: " + key + " " + value.toString());
      response.addHeader(key, value.toString());
   }
}

Ans Jersey in org.glassfish.jersey.message.internal.HeaderUtils:

public static String asString(final Object headerValue, RuntimeDelegate rd) {
    if (headerValue == null) {
        return null;
    }
    if (headerValue instanceof String) {
        return (String) headerValue;
    }
    if (rd == null) {
        rd = RuntimeDelegate.getInstance();
    }

    final HeaderDelegate hp = rd.createHeaderDelegate(headerValue.getClass());
    return (hp != null) ? hp.toString(headerValue) : headerValue.toString();
}

In both cases the toString() method of the header classes will not be used since createHeaderDelegate() is required to return a value for them.

And I don't see any use case for them as a user of the JAX-RS Api.
Could we just deprecate/remove them?
The static variable makes testing a lot harder and only causes problems e.g. when more than one implementation is on the classpath and is not a very nice design.

If rendering/parsing a header is required the HeaderDelegate could be used directly.

Is there any use case I am not seeing?

Best regards,

  Niklas