1-by-1 black pixel for creating lines
1-by-1 black pixel for creating lines
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No Cookies Required

As explained in How This Site Works, the HTML pages on this site are dynamically generated. This allows me to do some interesting things, such as automatically switching between a screen-friendly and a printer-friendly version of the site without writing two sets of pages. To do this kind of thing, however, my web application needs to track state information about your browser session. Normally, this is done using cookies, which are little pieces of server-generated data that get stored locally on your machine. Your browser sends the data back to the server every time it requests a page.

Encoding Session Information

While convenient, some people find cookies objectionable, for various reasons. HTTP, though, is a sessionless protocol, so if cookies are not available then you must do session tracking using other means.

One alternative to using cookies is to encode some kind of session identifier (ID) in the URL of the page. For example, given a URL like:


You could add a session ID using a query parameter:


Or you could add extra "path" information:


The latter approach is preferable, because then the session information doesn't get mixed up with the query parameters used by the site's forms. As it turns out, the HTTP specification makes this approach very easy to do because it allows the URL to append extra information to a URL path by separating it with a semicolon, like this:


URL Encoding in Java

The servlet specification makes it trivial to add this session information to the URL:

String url = "/about/index.html";
HttpServletResponse res = .... // some response

url = res.encodeURL( url );

From a JSP page, you can do this very easily using the JSTL <c:url> tag:

<c:url value="/about/index.html">

For the session tracking to work, though, you must encode every internal link in your site. In other words, every link you generate in your markup that goes to another page in your site must run through the encoding procedure. You can't do this kind of thing with static pages.

Note: this site will use cookies if they are available. But it will work just as well without them. If the servlet container (Tomcat, in this case) detects that cookies are enabled, the HttpServletResponse.encodeURL method simply returns the URL that was passed to it, without any additional encoding. It makes things pretty seamless!

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This page was last modified on September 3, 2003
1-by-1 black pixel for creating lines
1-by-1 black pixel for creating lines