Application scope variables ... an easier way or not ?

Instead of sharing application scope variables through the
          servletContext()/application I am using a normal singleton class (or maybe
          static class) to share all my application varaiable. It works fine and it
          takes a lot less code to write.
          It seamed logical to do this a static classes or singletons are shared
          within a single servletContext/application (which there seems to be only one
          per WL instance anyway). (singleton is quite nice pattern coz. all
          jsp:useBeans with the application scope are by definition singletons)
          Has anoyne tried something similar or maybe know of the problem with this
          approach. I assume that server will never reinitialise application level
          variables ...... hope the assumption is correct. ....

When you specify application scope, the JSP stores/retrieves the value
 into/from the servlet context. You may already know this, but it sounded
 like what you thought you were somehow avoiding.
 Cameron Purdy
 http://www.tangosol.com
 "Bohinc D" <[email protected]> wrote in message
 news:[email protected]..
 > Instead of sharing application scope variables through the
 > servletContext()/application I am using a normal singleton class (or maybe
 > static class) to share all my application varaiable. It works fine and it
 > takes a lot less code to write.
 >
 > It seamed logical to do this a static classes or singletons are shared
 > within a single servletContext/application (which there seems to be only
 one
 > per WL instance anyway). (singleton is quite nice pattern coz. all
 > jsp:useBeans with the application scope are by definition singletons)
 >
 > Has anoyne tried something similar or maybe know of the problem with this
 > approach. I assume that server will never reinitialise application level
 > variables ...... hope the assumption is correct. ....
 >
 >
 >

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Accessing Application Scope from an EJB

I'm not sure of the best way of doing this:
The set up:
We have a rather large J2EE application that is composed of only servlets and JSPs at the moment (When the application began development EJB was in its infancy and not feasible for the development of the app). Some of the new deployments of the app involve distributed webserver over 4 JVMs and 2 machines. When a user connects the servers load balancing decides which particular JVM they should be connected to. We perform large data caching into the servlet application scope to avoid having to access the database every time a change is made by a user to certain tables in our database. The data caches are stored in hashtables in the servlet application scope.We seem to have no way to determine what other JVMs are running or which JVM a user is currently connected to.
The problem:
Apparently the application scope is for a particular JVM. This means that when a user makes a change to a data cache the change doesn't effect users in the other 3 JVMs of the application, only the users who, due to load balancing, happened to be connected to the same JVM as the one where the change was made.
Our possible solution:
We were thinking that we could set up a queue (such as MQSeries from IBM) and any time a change is made to one of these data caches put a message on the stack saying that the particular table had been updated. Then a MDB would be listening asynchronously and digest the message from the Queue and recache the tables from the database.
So here are my questions:
1. Would this work? Would putting a MDB in the EJB Container give each JVM the MDB in the first place, or would this mean it would pick one of the JVMs to deploy the MDB on and still not fix our problem.
2. If this does work, how do I access the hashtables stored in the Servlet Application scope from the MDB. I can't seem to find any method available to the MDB (or any EJBs for that matter) that can access the servlets Application scope.
3. Is this the best way to do this? Or is there a better way to share data between seperate JVMs that I don't have a URL to (It's all ambiguous and handled by the server as to which JVM actually gets the connection.)
Just in case this is needed:
We are running IBM WebSphere 5 Application Server and the database could be anything from DB2 to Oracle.
Thanks in advance for any possible help.

You wont get any api for directly accessing Servlet application objects from any ejb. I dont think MDB either solves your problem directly. Indirectly you can place a request to some servlet (should be there for each JVM and web application ) and update your application scope variable. I would suggest you to cache the data in database if the size of cache is large. otherwise any open caching tools may help you.

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300 requests per hour reading from Application scope Good/Bad idea

I am saving some html in application scope & reading with
<cflock readonly.
Will it be a problem if more than 5 requests are made per
second?
Does deadlocks occurs with readonly-cflock?
Thanks

While creating/changing application scope variables in a
lock, I think there must be an exclusive lock. You must be careful
not to set any shared variable such as application inside a read
only cflock tag.
I also would suggest to check the usage of Application.cfc
and onApplicationStart method. You can set application default
variables and constants in onApplicationStart method in your
Application.cfc.

Application Scope within onSessionEnd

Hi,
Can someone enlighten me as to why application scope variables cannot be directly referenced from onSessionEnd? I can understand session variables being unavailable in onSessionEnd, but shouldn't application scope vars still be available? Why do we need to pass them as arguments into onSessionEnd?

Dave Watts wrote:
If onSessionEnd is single-threaded, the value of Application will be the same throughout the function unless the function itself changes it. So, again, no, there's no coarse- vs fine-grained distinction to be made here.
OnSessionEnd can not be single-threaded, at least, not in this respect. I don't need Adobe to tell me that.
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You wont get any api for directly accessing Servlet application objects from any ejb. I dont think MDB either solves your problem directly. Indirectly you can place a request to some servlet (should be there for each JVM and web application ) and update your application scope variable. I would suggest you to cache the data in database if the size of cache is large. otherwise any open caching tools may help you.

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Hi All,
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I was thinking of using ContextListener, but you dont have access to the faces context in the listener.
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Any ideas on how this can be achieved.
Thanks for your help!!

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try{
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sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
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sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
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Gedomir,
Thanks for the reply. But unfortunately it did not work. I was using the default initial context. I tried setting the properties as well. Even then it did not work.
I am trying this with oc4j_extended.
Thanks again.

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Application scope variables ... an easier way or not ?

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