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public class CellQuotes extends HttpServlet
{
   public void doGet(...) throws ServletException
   {
      // return HTML Form to user
      // We do this by simply reading a local file and dumping it
      // to the response stream
   }

   public void doPost(...) throws ServletException
   {
      // extract profile information from POST
      // assume its already been validated by JavaScript on client
      // save parameters as new Profile object
      ...
      // Write the profile to disk
      writeProfile(profile);
      ...

      // clean up
      ...
   }

   private void writeProfile(Profile p)
   {
      // synchronize on some static object, so that multiple servlet
      // instances don't corrupt profiles file

      synchronized(obj)
      {
         // check for existence of LockFile
         if(Constants.lockFile.exists())
         {
         // waiting and timeout code goes here
         }

         // Since access is available, create lockfile and write to
         // transaction file
         ProfileWriter pw = new ProfileWriter(Constants.transactionFile);
         prw.writeProfile(p);
         ...
      }
   }
}

public class TimeWorker
{
   private static int counter = 0;

   public static void main(String argv[])
   {
      // we want the application to run continuously, so enter an
      // infinite loop

      while(true)
      {
         // check if Transaction file exists
         // if yes, then new profiles must be merged with main store
         if(Constants.transactionFile.exists())
         {
            // check if lockfile exists
            if(Constants.lockFile.exists())
            {
            // waiting and timeout code goes here
            ...
            }

            // We have access to transaction file, so create lockfile
            // and merge profiles
            ...
         }

         // Main store is up-to-date

         while(...) // loop to read all user profiles
         {
            // read next profile
            // check if user is "eligible" to be sent quotes
            if(...)
            {
               // get quotes for user's stock symbols from quote.yahoo.com
               // get CellProvider implementation from CellProviderSelector
               // factory
               CellProvider prov = CellProviderSelector.getCellProvider(profile.getProviderID());

               // send quotes to this handler, which then sends SMS message
            }
         }

         // All user-profiles have been dealt with, sleep now

         counter++;
         try
         {
            // sleep for an hour
            Thread.sleep(1000*60*60);
         }
         catch(InterruptedException ie)
         {
            ...
         }
      }
   }
}

Resources
Download the source code that accompanies this article:
http://www.javaworld.com/javaworld/jw-03-2001/sms/jw-0330-sms.zip

Global mobile phone growth report:
http://home.intekom.com/cellular/stats/statistics_global_handset_sales_2000.htm

The Internet Economy Indicators report, June 1999:
http://www.internetindicators.com/features.html

"What Services Do Wireless Data Users Want?" (internet.com, March 23, 2000):
http://www.allnetdevices.com/marketdata/000323wireless.htm

A comprehensive introduction to SMS:
http://www.anywhereyougo.com/ayg/ayg/sms/Index.po

The Lycos Free SMS Service page:
http://www.lycos.co.uk/service/sms/agb.html

The WAP Forum:
http://www.wapforum.com

"Companies Seek to Bridge 'WAP Gap,'" (internet.com, March 24, 2000):
http://www.allnetdevices.com/news/0003/000324wap.htm

See the findings of the Tamkang University department of mass communications's survey of WAP-enabled cell users -- "Taiwan Survey: WAP Considered Expensive & Slow," Steve Crook (internet.com, April 11, 2000):
http://www.allnetdevices.com/news/0004/000411taiwan.htm

To find out why SMS still rocks -- "SMS Still the Killer App," Jørgen Berner Ross (wap.com, November 14, 2000):
http://www.wap.com/cgi-bin/view.cgi?id=300302&cat=7

To find out why Microsoft rejected WAP -- "Microsoft Compares WAP with DOS," John Leyden (vnunet.com, July 6, 2000):
http://thebusiness.vnunet.com/news/1105882

Read this article to learn why WAP fails -- "One Wireless Viewpoint: 'WAP is Crap,'" Nicole Manktelow (ZDNet UK, June 30, 2000):
http://www.zdnet.co.uk/news/2000/25/ns-16330.html

"WAP for Java Developers," Qusay H. Mahmoud (JavaWorld, June 2, 2000):
http://www.javaworld.com/jw-06-2000/jw-0602-wap.html

"Give WAP a Break," Joanie Wexler (ITworld.com, January 17, 2001):
http://www.itworld.com/Net/3025/NWW00319216/

For more articles on wireless technologies, browse the Embedded Java section of JavaWorld's Topical Index:
http://www.javaworld.com/javaworld/topicalindex/jw-ti-embedded.html

Talk more about SMS and WAP in the Device Programming discussion, moderated by Qusay Mahmoud:
http://www.itworld.com/jump/jw-0330-sms/forums.itworld.com/webx?230@
@.ee6b808!skip=155

Sign up for the JavaWorld This Week free weekly email newsletter and keep up with what's new at JavaWorld:
http://reg.itworld.com/cgi-bin/subcontent12.cgi

Read more from Sonal Bansal and Gaurav Pal: "Exceptions in Java: Nothing Exceptional About Them," (JavaWorld, August 18, 2000):
http://www.javaworld.com/jw-08-2000/jw-0818-exceptions.html

Read more from Gaurav Pal: "HMVC: The Layered Pattern for Developing Strong Client Tiers," (JavaWorld, July 21, 2000):
http://www.javaworld.com/jw-07-2000/jw-0721-hmvc.html