How do I write a J2EE/EJB Singleton?
- by Bears will eat you
A day ago my application was one EAR, containing one WAR, one EJB JAR, and a couple of utility JAR files. I had a POJO singleton class in one of those utility files, it worked, and all was well with the world:
EAR
|--- WAR
|--- EJB JAR
|--- Util 1 JAR
|--- Util 2 JAR
|--- etc.
Then I created a second WAR and found out (the hard way) that each WAR has its own ClassLoader, so each WAR sees a different singleton, and things break down from there. This is not so good.
EAR
|--- WAR 1
|--- WAR 2
|--- EJB JAR
|--- Util 1 JAR
|--- Util 2 JAR
|--- etc.
So, I'm looking for a way to create a Java singleton object that will work across WARs (across ClassLoaders?). The @Singleton EJB annotation seemed pretty promising until I found that JBoss 5.1 doesn't seem to support that annotation (which was added as part of EJB 3.1). Did I miss something - can I use @Singleton with JBoss 5.1? Upgrading to JBoss AS 6 is not an option right now.
Alternately, I'd be just as happy to not have to use EJB to implement my singleton. What else can I do to solve this problem? Basically, I need a semi-application-wide* hook into a whole bunch of other objects, like various cached data, and app config info. As a last resort, I've already considered merging my two WARs into one, but that would be pretty hellish.
*Meaning: available basically anywhere above a certain layer; for now, mostly in my WARs - the View and Controller (in a loose sense).
