It is therefore becoming more important than ever that information displays are updated when the data they show changes.
So far we've discussed simple local database access from Java using JDBC, and various approaches for connecting Java agents to remote databases.
Some simple extensions to these approaches allow you to connect a Java agent to multiple remote databases, and create some interesting possibilities for applications in data analysis and management.
Interested objects can inform the Account DAO object that they want to be informed about changes, and it will then call them back with details of each Account object it stores in the database.
Listing 3: Account DAO changes (); private Account make Account (Result Set result Set) throws SQLException public boolean create (Account account) throws SQLException public boolean update (Account account) throws SQLException public List get By Customer Updated Since (int id, Date since) throws SQLException public void add Listener (Account Change Listener listener) public void remove Listener (Account Change Listener listener) private void notify Change (Account changed) static String projection () } Each method has been updated to take into account the existence of the new balance Updated column, and I have added the listener interface Account Change Listener (which has only the single method account Changed(Account)) and the methods to manage the set of listeners.
In this article, I will describe a few of the possible methods of implementing this kind of feature, but before beginning we need to ensure we have a suitable application.
I will describe the variation in more detail later, but for now you may consider it important to understand the basic approach that I describe in that article.There are two basic approaches we can use: we can add a timestamp field to each record and update it whenever we update the record, or we can use a sequentially-incremented number.I have chosen the former, because it is simpler to implement, but it is worth bearing in mind that this approach has a few drawbacks: it only works if all the servers the application runs on have synchronized clocks, and it can become confused if updates occur multiple times within the resolution of your clock.For an application with a single server, infrequent updates, and a tolerance for occasional failures, it is appropriate however.Update sequence numbers are more complicated to implement, because you need a source of sequence numbers that is guaranteed to increase monotonically.Whether supporting executives in business decision making, providing customer support operatives with up-to-date status information, or allowing customers to make purchase decisions, accurate data is essential.