Creating Etags via ContainerResponseFilter

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Creating Etags via ContainerResponseFilter


I have been having some difficulty implementing etags in a ContainerResponseFilter and was hoping I can get some assistance.  So far I have implemented the following filter method. 

public ContainerResponse filter(ContainerRequest containerRequest, ContainerResponse containerResponse) { 
        logger.debug("request URI: "+containerRequest.getAbsolutePath()); 
        if (isEligibleForEtag(containerRequest, containerResponse)) { 

                Object entity = containerResponse.getEntity(); 
                Object originalEntity = containerResponse.getOriginalEntity(); 
                java.lang.reflect.Type entityType = containerResponse.getEntityType(); 
                if (entity != null) { 
                        EntityTag etag = generateETag(originalEntity); 
                        Response.ResponseBuilder responseBuilder = request.evaluatePreconditions(etag); 
                        if (responseBuilder != null) { 
                            logger.debug("entity has not changed so returning unmodified response code"); 
                        } else { 
                            responseBuilder = containerResponse.getResponse().fromResponse(containerResponse.getResponse()); 

        return containerResponse; 

The first problem is that the filter is called before the serialization of the entity so there isn't a good way to get the bytes required to calculate a strong etag.  I could create a ServletFilter to manage this instead, but wanted to confirm I wasn't missing something in the Jersey framework as that is the preferred approach. 

The next problem is with setting the etag in the ConatainerResponse.  I didn't see a straightforward way to do this, but I certainly could have missed something.  As you can see in the example above I made a shallow copy of the ContainterResponse Response object to create a Response.ResponseBuilder to add the etag.  Is there a better way? 

Thanks in advance for your assistance as we really enjoy Jersey.