Java Thread Management and Application Flow

Question

I have a Java application that downloads information (Entities) from our server. I use a Download thread to download the data.

The flow of the download process is as follows:

1. Log in - The user entity is downloaded
2. Based on the User Entity, download a 'Community' entities List and Display in drop down
3. Based on Community drop down selection, Download and show 'Org Tree' in a JTree
4. Based on Node selection, download Category entities and display in drop down
5. Based on Category selection, download Sub Category entities and display in drop down
6. Based on Sub Category selection download a large data set and save it

The download occurs in a thread so the GUI does not 'freeze'. It also allows me to update a Progress Bar.

I need help with managing this process. The main problem is when I download entity data I have to find a way to wait for the thread to finish before attempting to get the entity and move to the next step in the app flow.

So far I have used a modal dialog to control flow. I start the thread, pop up a modal and then dispose of the modal when the thread is finished. The modal/thread are Observer/Observable the thread does a set changed when it is finished and the dialog disposes. Displaying a modal effectively stops the flow of the application so it can wait for the download to finish.

I also tried just moving all the work flow to Observers. All relevant GUI in the process are Observers. Each update method waits for the download to finish and then calls the next piece of GUI which does its own downloading.

So far I found these two methods produce code that is hard to follow. I would like to 'centralize' this work flow so other developers are not pulling out their hair when they try to follow it.

My Question is: Do you have any suggestions/examples where a work flow such as this can be managed in a way that produces code that is easy to follow?

I know 'easy' is a relative term and I know my both my options already work but I would like to get some ideas from other coders while I still have time to change it.

Thank you very much.

Answer 1

You might want to look into using the Future interface. Stop by http://download.oracle.com/javase/6/docs/api/java/util/concurrent/package-summary.html It has all you might need to make these tasks easier.