About the PIA's Servlet implementations

The PIA includes two implementations of the Servlet interface: PIAServlet and DPSServlet.

1. PIAServlet is as faithful an implementation of the PIA server as is feasible within a Servlet engine environment: it reads a PIA configuration file, sets up the Site structure, and essentially takes over. It should be mapped onto the root of the server's URL (virtual path) tree. About the only thing it doesn't do is run agents on proxied requests.
2. DPSServlet assumes that its context can map a URL onto a file, and simply runs that file through the DPS. The only complication is the need to construct the table that maps filenames into tagsets.

Configuration

So far, PIAServlet has only been tested in Apache-JServ and Sun's servletrunner in JSDK2.0. Because PIAServlet is still highly experimental, it should be configured with a path to a file that it uses as a log file. Configuration files for JServ can be found in PIA/Config/Servlet. If you run the PIA under servletrunner you must tell it where to find the tagsets (the home initialization parameter), otherwise it will fail with a null pointer exception whenever it tries to load a tagset.

The biggest problem with PIAServlet so far is that a Servlet is effectively a subdirectory, and JServ has no way to ``mount'' a Servlet on the server's root. There are two main ways of dealing with this:

1. Use mod_rewrite or the equivalent to map pathnames onto the PIA servlet. This pretty-well renders your server useless for serving ordinary files, so you may as well just use the PIA server.
2. Use the PIA:url and PIA:rootPath entities in your .xh files to refer to the Servlet root. The entities are defined correctly both in the standalone PIA and in the PIAServlet. This allows a PIA-based application to co-exist with other applications in your server.

Testing

Assuming you have JSDK2.0 and servletrunner, you can start the server with the command:

 /usr/local/JSDK2.0/bin/servletrunner -r ~/PIA

and point your browser to:

 http://localhost:8080/servlet/org.risource.servlet.PIAServlet/

To-Do list

• Impr URL space for include, etc. still rooted at /
  ... instead of PIA:rootPath, which might be more consistent. Right now paths used for tagsets and include files that start with "/" are relative to the servlet rather than the server. (2000-04-18)
• Impr Logging uses a PrintStream.
  really need to have a logger class that can pass the buck to the servlet. There should be a static pointer to it, i.e. Log.logger, so that classes like tagset.Loader and TopProcessor can find it. (2000-04-05)

done

• 2000-04-12 Bug DPSServlet has no tagset mapping.
  Should take tagset.ext=tsname and type.ext=mime-type initialization parameters. (2000-04-05)
• 2000-04-13 Bug No PIA namespace in PIAServlet
  (2000-04-05)
• 2000-04-14 Bug Site cannot be a subdirectory.
  currently need to use mod_rewrite to map /xxx to /PIA/xxx. (2000-04-05)
• 2000-04-18 Bug Doesn't handle queries.
  This one's serious. (2000-04-18)