Java Web Service HttpServletRequestWrapper Issue: IllegalStateException

Question

I am currently developing a RESTful Webservice in Java using the Jersey library.

For security reasons, we want a custom authentication similar to Amazons Simple Storage Service. This requires, however, that I calculate an MD5 hash of the body (if there is any) to authenticate the request.

So far, I have used a custom Authenticator and Realm and plugged them into my context. Upon trying to calculate the hash I first used the request itself resulting in an IllegalStateException, since the body can only be read once.

After investigating the problem I tried to wrap the request inside a HttpServletRequestWrapper but hasn't been successful so far.

I am basically using a wrapper like the one shown here: http://forums.oracle.com/forums/thread.jspa?threadID=2156814&tstart=0

Inside my realm, where I do the authentication, I am first creating the wrapper like so:

MyRequestWrapper requestWrapper = new MyRequestWrapper(request);

then I am calculating the MD5 using the requestWrapper and finally forwarding it

request.getRequestDispatcher("/*").forward(requestWrapper, response);

The processing works fine but I get an error like this after that:

Servlet.service() for servlet Jersey REST Service threw exception
java.lang.IllegalStateException
    at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:407)
    at com.sun.jersey.spi.container.servlet.WebComponent$Writer.finish(WebComponent.java:285)
    at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:241)

Note that there is no mentioning of the getReader or getInputStream being called before (like I got without using any wrapper at all).

Now I am sure I am doing something wrong here but I really don't know much about this and would be really glad if someone could help me out here :)

Best Regards, Lukas