This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
A URL is used in a request, not a response. Assuming your really mean request header, look at the JavaDocs for the javax.servlet.http.HttpServletRequest interface. There you will find methods such as: getHeader( String hdrname ); and other related methods. Anybody working with servlets should have a copy of the related JavaDocs - they come with Tomcat installations automatically.
If on the other hand you are talking about the URLConnection class in the java.net package, you will find methods such as getHeaderField( String name). JavaDocs for the java.net package can be downloaded from the same place as the SDK - everybody working with Java should have them. Bill