When a Servlet creates a response which contains a relative URL, e.g. a hyperlink in an HTML document, you have to make sure that the URL points to the right directory.
Example. The following document is mounted on a server as /shop/preview/form.html:
<HTML><HEAD><TITLE>Form</TITLE></HEAD><BODY> <FORM ACTION="/servlet/PreviewServlet" METHOD=GET> ... </FORM> </BODY></HTML>
There are also product images in the same directory, e.g. /shop/preview/foo.gif, /shop/preview/bar.gif, …
The Servlet which is mounted as /servlet/PreviewServlet evaluates the form data and creates an HTML page with IMG tags to the appropriate product images, e.g. <IMG SRC="foo.gif">. But this naive approach does not work. The images are in the same directory as the form but the page is created by the Servlet, so the client sees it as /servlet/PreviewServlet. The base name of this URL is /servlet/, thus the image foo.gif from the above image tag is expected at /servlet/foo.gif and not /shop/preview/foo.gif. If /servlet/ is a pure Servlet directory it can only contain Servlets and no other data (like GIF images). It is therefore not possible to move the images to the Servlet directory (/servlet/). Instead the image tags need to be modified to include the full path to the images, relative to the server root, i.e. <IMG SRC="/shop/preview/foo.gif"> for the foo.gif image.
