Progress

The callback object ProgressListener is used to report on long running operations and provide a chance for the end user to cancel them.

There are several implementations available in GeoTools:

  • ProgressWindow - provides a swing dialog showing operation progress
  • ProgressPrinter - reports operation progress to standard out
  • ProgressMailer - will email when the operation is completed

As you can see these really are intended for operations that may take minuets to complete.

There are a couple implementations of direct interest to implementors:

  • NullProgressListener - null object to use when you are not interested
  • SubProgressListener - used by implementors when delegating a portion of work to a sub operation
  • DelegateProgressListener

Example use:

public void doSomething( ProgressListener progress ){
    if( progress == null ) progress = new NullProgressListener();

    progress.started();
    progress.setDecsription("Connect");

    ..connect to data store and obtain feature collection...

    progress.progress( 20 ); // connecting represents 20% of the work

    progress.setDescription("Process features");
    featureCollection.accepts( visitor, new SubProgress( progress, 80 ) );

    progress.completed();
}

This code could be called using:

  • doSomething( new ProgressWindow( null ) ); // from a Swing Application
  • doSomething( new ProgressMailer( mailserver, emailAddress ) ); // from a web application
  • doSomething( new ProgressPrinter() ); // for a command line application
  • doSomething( new NullProgressListener() ); // if you don’t care

Additional adapters for SWT project are available in the uDig project.

Using ProgressListener to Cancel

The ProgressListener is a general user interface callback object; as such it allows the a user to cancel a long running operation.:

final ProgressListener progress= new ProgressWindow( null );
Thread worker = new Thread( new Runnable(){
    public void run(){
        doSomething( progress );
    }
});
cancel.addActionListener( new ActionListener(){
    public void actionPerformed( ActionEvent e ) {
       progress.setCanceled( true );
    }
});