In a multiple JVM’s environment, each of them will have their own copy of the singleton object which can lead to multiple issues specially in a clustered environment where the access to the resource needs to be restricted and synchronized.
To achieve clustering across multiple JVM’s, one can use multiple techniques (JMS, DB, Custom API, 3rd party tools), but each of them have an impact on the business logic.
- Application server’s also provide some level of custom API’s to circumvent this problem.
- Terracotta, Oracle Coherence are good options. These work on the concept of providing an in memory replication of objects across JVMs in effect providing you singleton view or making use of any of the cluster-aware cache provider’s like Swarm Cache or JBoss TreeCache should work as cache entries are singletons and clustering is built in.
- Also, there is product called JGroups – which uses mulch-cast communication (TCP/UDP). It allows to form a group and Applications (JVM’s) can participate and JGroups will send messages to everyone in the group so that they can be in sync.
- JBoss has has Singleton Service ( based on MBeans) which is meant to solve this problem. Check hereand here
- Weblogic has the concept of Singleton Service – where only instance runs within the cluster and all clients will look up to the same instance.
- WebSphere supports the concept of singleton across cluster in the WebSphere version of the application server as the partition facility – ObjectGrid