using util class that create thread in servlet

[zhiming jia]

Is it ok to call a utility class which creates threads to do its job in a servlet's doGet/doPost method? Any input appreciated.

[Vishal Pai]

Should not be a problem. I have done this a couple of times.

[Sripathi Krishnamurthy]

there is no case where a thread has to be created and used in a servlet.
Each servlet request has its "own" dedicated thread. This thread manages the entire cycle(doget/dopost) of a servlet.
Once the doget/dopost/service is complete, the request and response objects will no more be available. So cant use any of the objects which are of request and responce type.

[Ben Souther]

It's not recommended but it's done all the time.
Make sure to use daemon threads.

[Sripathi Krishnamurthy]

Ben,
Can you please give me instances where there is a requirement to create thread inside a servlet? and also how to create a thread as daemon?

Thanks

[James Carman]

How about a situation where you want to kick off a long-running process and you don't want to bog down the user's browser waiting for it (it might even time-out anyway)? In that situation, maybe you're going to email the user when you're finished to let them know that the results are available for review or just that the operation is finished. As for creating daemon threads, it's simple...

 
Thread t = new Thread( new OperationExecutor() );
t.setDaemon( true );
t.start();

The trick is what to do with this daemon thread. One idea might be...

  
public class OperationExecutor implements Runnable
{
  private final LinkedList queue;
 
  public OperationRunner( LinkedList queue )
  {
    this.queue = queue;
  }
 
  public void run()
  {
    while( true )
    {
      Runnable operation = null;
      synchronized( queue )
      {
        while( queue.isEmpty() )
        {
          try
          {
            queue.wait();
          }
          catch( InterruptedException e )
          {
            return;  
          }
        }
        operation = ( Runnable )queue.removeFirst();
      }   
      operation.run();
    }
  }
}

In your servlet code, then, you would do something like...

  
synchronized( queue )
{
  queue.addLast( new LongRunningOperationWhichImplementsRunnable() );
  queue.notify(); 
}