Java Desktop Application For Network users [closed]

is there a way to update user B screen with the new value?

Yes. This could be done in one of two ways:

1. The client application polls the data source and displays the results. This is pretty simple to implement, but the downside is the client must request new data every n seconds and then determine if there is any difference and refresh the display if there is.

2. The client subscribes to be notified by the server if something changes. Harder to implement - I think you'd have to build a server-side process to handle this.

if user A start updating Record, then prevent user B from updating at same time.

I will assume that it could take several minutes for User A to update the record by modifying data in a form. In this case, when a user chooses to edit a record, you need to mark it in the database as being edited. You could do this by explicitly locking the record in the database, though how to do this will depend on what database you're using.

You could also use soft locks. This would involve having a table to indicate which records are locked and when another client tries to edit a record, it must first check that there is no lock recorded:

customers
---------
  ID (PK)
  (other fields)

customer_locks
--------------
  ID (PK)
  customer_id (FK to customers.id)
  client_id (String to identify which client system has locked the record)
  lock_timestamp

So when a client system wants to edit a customer with some ID, it must first check that there is no existing record in customer_locks. Then it creates a record for itself (if there are no locks - if there are, the client must be notified). Then it (eventually) does an UPDATE... for the customer in question, then it must delete the lock record.

Of course, then you have questions about what happens if a client is disconnected after they create a lock? You can use lock_timestamp to time out any old locks with a scheduled job.

Really, you're best off writing a small server-side process to handle all of this. I once tried to do similar stuff purely on the client-side (with the help of a couple of small stored procedures) and it worked but it was painful and complicated. A proper server-side process would have been much better.