As of the 6.1 release, Sun Java System Web Server extends the Netscape Server Application Programmer's Interface (NSAPI) to support NSAPI filters.
Filters enable the custom processing of HTTP request and response streams, allowing a function to intercept and potentially modify the content presented to or generated by another function. For example, a plug-in could install an NSAPI filter to intercept an XML page generated by another plug-in's Server Application Function (SAF), then transform that XML page into an HTML, XHTML, or WAP page appropriate for the client. Alternatively, an NSAPI filter could decompress data received from a client before presenting it to another plug-in.
For more information, see Sun Java System Web Server 6.1 SP4 NSAPI Programmer’s Guide.