How the attribute field of a HttpServletRequest maps to a raw HTTP request?

Question

In Java, the attribute field of a HttpServletRequest object can be retrieved using the getAttribute method:

String myAttribute = request.getAttribute("[parameter name]");

Where the HttpServletRequest attribute data is stored in a raw HTTP request? Is it in the body of the request?

For example, I'm trying to create a raw GET HTTP request that will be sent to my servlet using some client program. My servlet.doGet() method would be something like this:

public void doGet(HttpServletRequest request, HttpServletResponse response)
{
     String myAttribute = request.getAttribute("my.username");
     ...
}

Where should I put the 'my.username' data in the raw HTTP request so that the 'myAttribute' String receives the value "John Doe" after the attribution?

Answer 1

Just to be clear as I think @Jon's answer doesn't make it perfectly clear. The values for getAttribute and setAttribute on HttpServletRequest are not present on what is actually sent over the wire, they are server side only.

// only visible in this request and on the server
request.getAttribute("myAttribute"); 

// value of the User-Agent header sent by the client
request.getHeader("User-Agent"); 

// value of param1 either from the query string or form post body
request.getParameter("param1"); 

Answer 2

To add to @gid's answer, attributes are not present in any way in the HTTP request as it travels over the wire. They are created (by your code) when processing the request. A very common use is to have a server set (aka create) some attributes and then forward to a JSP that will make use of those attributes. That is, an HTTP request arrives and is sent to a Servlet. The Servlet attaches some attributes. Additional server-side processing is done, eventually sending the page to a JSP, where the attributes are used. The response is generated in the JSP. The HTTP request and the HTTP response do not contain any attributes. Attributes are 100% purely server-side information.

When a single given HTTP request has completed, the attributes become available for garbage collection (unless they are persisted in some other location, such as a session). Attributes are only associated with a single request object.