Asynchronous continuous polling of data from DB pushed to Java-client

Question

Could someone suggest what’s the best approach to go about this:

What I like to do is draw a continuous poll (or query) of a database table. And anytime a new update has occurred, I want to push this to the client in a Java application. The idea is users can suggest what data they want to subscribe to and define an event-handler to handle any incoming data.

I therefore need to have the polling being done in the background. But I seem to having trouble with doing this correctly. I’m looking at using a simple event bus for local JVM pub/sub, but I can’t seem to get the asynchronous continuous polling going.

@Jonas At the moment it is just a Java library. Where I want users to define an event-handler to handle events they want to subscribe to. On the publishing side, new entries in the table act as events coming in. — Larry
– Larry, Commented Jul 24, 2011 at 15:50
@toto What’s the differences between this and what jiggy suggested below (i.e using a ScheduledThreadPollExecutor)? — Larry
– Larry, Commented Jul 24, 2011 at 16:00

Hovercraft Full Of Eels · Accepted Answer · 2011-07-24 15:49:10Z

2

Your solution has a lot of disadvantages.
A better solution is to create business logic that is responsible for saving data in the database and for notifications. You can for example create an application that is subscribed to JMS topic. Another component receives calls to process and save data. It stores data and then sends notification of this action. All components subscribed to the topic receive this notification and react accordingly.

edited Jul 24, 2011 at 15:49

Hovercraft Full Of Eels

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answered Jul 24, 2011 at 15:45

AlexR

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3 Comments

jiggy Over a year ago

That'a assuming his app is also responsible for populating the data.

Larry Over a year ago

Thanks, but JMS seems too complicated to implement. Is there a more simple solution? That is why I was thinking of a simple ESB like code.google.com/p/simpleeventbus, but I’m stuck trying to get a continuos poll/read of the DB?

Larry Over a year ago

@jiggy That is right, populating the Data happens via a different app. I am aiming for this to be a client-side application connected to the DB to get events, via new entries in the DB table.

jiggy · Accepted Answer · 2011-07-24 15:50:38Z

1

Have a look at java.util.concurrent. You can create a scheduler to run at a given interval utilizing a thread pool like with a ScheduledThreadPoolExecutor.

answered Jul 24, 2011 at 15:50

jiggy

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2 Comments

Larry Over a year ago

thanks, do you happen to know of any good examples/sample code on the web for this?

jiggy Over a year ago

@Larry, just look a this javadoc for a good example of a scheduled job. Instead of beeping, you can read your DB. Note that the Runnable class is defined inline for terseness, but it can be defined in it's own .java file and just instantiated here.

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