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From Albert Kam <>
Subject Re: [OT] Observer pattern?
Date Wed, 13 Jun 2012 04:12:48 GMT
If you are talking about how to notify other webapps, i think you're
actually talking about integration between existing applications here,
which can be done using RMI (java only and using a specific port),
Hessian/Burlap (support several languages + http, but not java
serialization) , or even Spring's HttpInvoker (java + spring + use
But i think it's more usual for people to just implement web services,
either the RESTful way or the SOAP way, which makes use of HTTP (which
doesnt normally get blocked by firewall).

But if the weight of your question is on the observer pattern, which
is kinda like publish / subscribe,
for example, publishing change event, and the listener of that type of
event will execute some code (perhaps invoking external web services),
i suggest you to look at google guava's EventBus

Updating the view without user intervention is about realtime user
experience, which could involve polling or pushing changes. I am not
quite familiar in this, but i think polling is about using a smart
timer in javascript to fetch any data changes and then update the view
For pushing data from backend to frontend, perhaps html 5's websocket
could do, and perhaps comet also ?

On Wed, Jun 13, 2012 at 5:00 AM, Leo Donahue - PLANDEVX
<> wrote:
> Could someone point me in the right direction.
> If three different web applications all rely on knowing when a piece of data changes,
how does webapp #1 who makes the update, notify webapp #2 and webapp #3 that they need to
make a request to update their view?
> For example:
> User of webapp #1 updates the status of something in a database and needs to inform the
users of webapp #2 and webapp #3, who are updating other data yet watching for that status
to change, that they need to update their view (fetch updated data from a database, or call
some other method based on the changed status value).
> It sounds like the Observer pattern, but I don't know.
> Leo

Do not pursue the past. Do not lose yourself in the future.
The past no longer is. The future has not yet come.
Looking deeply at life as it is in the very here and now,
the practitioner dwells in stability and freedom.
(Thich Nhat Hanh)

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