POST required header info

I'm attempting to have some java code send a post request to a php script, but the variables are not being assigned correctly. The request comes through fine, but the vars keep coming up empty. The java code works fine with a perl script that grabs the post vars, as well as from a simple html form submitting post requests to the script. The only possible answer we've come up with some missing header information. Does anyone know where I can find a list of header requirements, or have encounter this type of problem before. Using GET is not an option.