Thanks Christian, Let me give you a specific example of what I am trying to do.
I have several different sets of label/value pairs that are stored in database tables. These label/value pairs make up the select options and other interface options for web pages in the application. The options do not change that often, so rather than going back to the database each time a page is displayed, I'd like to store the options in maps that are stored in application scope and easily accessible through JSTL. On the occasion that the options do change, I'd like to reload the applicable maps to all servers in the cluster. It seems like this would be a good feature for Tomcat to have, but from reading the documentation it seems that the feature is not there. Perhaps some sort of JMS broadcast service would do the trick. Does any one have any suggestions? Mike --- Christian Bollmeyer <[EMAIL PROTECTED]> wrote: > On Saturday 10 April 2004 21:48, Mike Duffy wrote: > > Hi, > > > I've read documentation for The Tomcat 5 Servlet/JSP Container: > > Clustering/Session Replication HOW-TO > > http://jakarta.apache.org/tomcat/tomcat-5.0-doc/cluster-howto.html > > > > I understand clustering for individual user sessions. Are there any > > correlated methods for clustering application scope objects? > > AFAIK there's nothing in the Servlet API specifications in this > direction. Sessions may be swapped in and out by several > different means (serialization or database), but application > scope information is kept individually for each JVM. > > > The J2EE API for the Interface ServletContext states, "In the case of > > a web application marked "distributed" in its deployment descriptor, > > there will be one context instance for each virtual machine. In this > > situation, the context cannot be used as a location to share global > > information (because the information won't be truly global). Use an > > external resource like a database instead." > > Yes. But then, it makes no difference whether your application > is marked as 'distributable' or not when considering application > scope objects. Application scope is always limited to a single > JVM. 'Distributed' is about sessions only. > > > Rather than use a database, what I would like to be able to do is > > make a call to > > > > servlet.getServletContext().setAttribute(key, object); > > > > and have the object stored in the application scope of all servers in > > the cluster. > > That surely would be desirable, but I don't know of any > 'official', declarative means to achieve such behavior. > Then: automatically synchronizing application scopes > between several JVM instances would cause a lot of > additional synchronization troubles - who determines > what's the actual system state at a given point, e.g. > if you update an application scope object (that is > globally shared) on one server, and another user > does likewise on a second one, what should be > the end result? And so on. > > > I know that EJBs were designed to serve this purpose; however, I > > would like to bypass the overhead and complexities of EJBs. > > EJBs live in the backend and are independant from > the web tier. Looking at the problem from a > web tier view (which is what Struts is about), > it should not make any difference whether the > information comes directly from a database > in the end or from an EJB tier in-between. > That's transparent. Anyway, using EJBs > won't solve your problem in the end, for > it's an entirely web tier specific issue, > and EJBs are not part of that. > > > If there isn't a switch that can be flipped in Tomcat, there might be > > a way to create a lightweight JMS administration class to serve this > > purpose. Has anyone tried this? > > There is no switch (remember the spoon > boy in Matrix I ? :-). But the JMS idea is > interesting. Never actually tried it, but > of course, you can always handle > application specific logic programma- > tically, including using JMS for updating > application scopes in a distributed > environment. But I never tried. > > > If the answer to this question is RTFM, please send a link; I've > > looked through the documentation and I can't seem to find a clear > > reference. > > > > Thanks for your time and consideration. > > Just some thoughts that came to me > on early Easter Sunday :-) Let's better > say: night; it's 2:16 local time here. So > I should better go to bed. > > > Mike > > HTH, > -- Chris. > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/ --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
