Sending POST request to Cougaar Servlet

[Todd Wright]

This is due to the way HTTP POST redirects work, and you'd see this in Tomcat 
if your servlet required redirection:

Cougaar Developers' Guide 10.2 page 105 (section 5.2 bullet 8):
   8. Here  are some important notes on the use "GET v.s. POST v.s. PUT"
       as the HTTP request method:

       HTML-generating  servlets  should only use "doGet(..)", where HTML
       "<a  hrefs=..>" are the same as before, but HTML FORMs should look
       like:
            <form method="GET" .. />  not POST!
            ... various "input" and "select" statements
            </form>
       Java clients that simply use URL-parameters can without writing to
       the  servlet  can  remain  as-is,  since HTTP GET works fine. Java
       clients  that  need  to  upload  data  to  the  servlet,  such  as
       serialized  Java  Objects  or  a streamed 'dialog', should use PUT
       instead of the default POST method:
             UrlConnection uc = ...;
             ((HttpUrlConnection) uc).setRequestMethod("PUT");
              OutputStream os = uc.getOutputStream();
              ...  // usual "upload-data" code
       and  the  servlet should support the "doPut(..)" method. Note that
       the  UrlConnection's  setting of the "GET v.s. POST" method is not
       well documented in the Sun javadocs.

       The  reason  for  the  above  "use  GET & use PUT instead of POST"
       nonsense  is  that  POST  requests  will not be redirected between
       nodes  (typically the POST data is lost), whereas GET and PUT will
       be  correctly  redirected.  The exact redirection rules are in the
       HTTP  specification  and built into the browser/URLConnection code
       itself:

       HTTP/1.1 spec on request methods:
           http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html

       Further notes on POST redirection:
           http://ppewww.ph.gla.ac.uk/~flavell/www/post-redirect.html

POST works fine if you find the specify the *correct* host:port in the URL 
(i.e. zero redirects are needed).  This is awkward if you have a multi-node 
society.

I haven't tried this, but I think you can turn off automatic 
HttpURLConnection redirection and do your own redirect if necessary.  Set the 
HttpURLConnection's "setInstanceFollowRedirects(false)", then check the 
HttpURLConnection's response code.  If the response is in the 300's (e.g. 
302), then your POST data was dropped and the HTTP response should include a 
"Location:" header with the redirect URL.  Then make a new connection to the 
redirect's URL and try the POST again.

You'll still need to handle the case where the agent *just* moved, in which 
case the POST parameters will be lost again.  This is usually better than 
having the UI attempt to cache these redirect URLs.

If there's lots of POST data then you may want to use an explicit "check for 
redirect" HTTP GET request before attempting the POST.

Todd

On Tuesday 11 March 2003 16:54, Stute, Nick J. wrote:
> I am trying to programmatically send a POST request to a Servlet running on
> one of my agents. I cannot seem to get the parameters to the Servlet. The
> sample code below works fine for a similar servlet running in Tomcat (not
> in Cougaar).
>
> I successfully connect to the servlet, but the parameters don't seem to
> make it.
>
> Here is the code that accesses the Servlet:
>
>       URL url = new URL( "http", "localhost", 8800, "/TestServlet");
>       URLConnection connection = url.openConnection();
>       ((HttpURLConnection)connection).setRequestMethod( "POST");
>       connection.setDoInput( true);
>       connection.setDoOutput( true);
>       OutputStreamWriter out = new OutputStreamWriter(
> connection.getOutputStream());
>       out.write( "MODE=AIRCRAFTASSETS&OUTPUT=HTML");
>       out.write( "\r\n");
>       out.flush();
>       out.close();
>       BufferedReader br = new BufferedReader( new InputStreamReader(
> connection.getInputStream()));
>       while ( br.ready()) {
>         System.out.println( br.readLine());
>       }
>
> Nick Stute
> Northrop Grumman Information Technology, DES
> Email: nstute at northropgrumman.com
> Phone: 937.431.5918
> Fax: 937.426.8888
>
>
>
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