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Singleton Pattern in Cluster

 
Abhishek Arya
Greenhorn
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Hi,
Can any body tell me the behaviour of Singleton Class in a Clustered Environment.
Let us suppose there are thee servers in a cluster, then whether the Singleton Class will be instanciated in each of the Cluster??
Regards,
 
eammon bannon
Ranch Hand
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Yes. The rule for a singleton is that it guarentees one intance per JVM. There are patterns out there which can make sure there is only one instance of a singleton in a cluster, but for most normal cases where you would use a singleton (i.e. a small amount of read-only data needs cached for your app) having an instance per JVM is not really a problem. If you have an occasion where you must have only one instance per clustered application, you can do this with RMI - deploying the singlton as a RMI service, and looking it up through JNDI.
 
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