I understand that web containers like jboss have a parameter to mention the number of threads of the servlet to create, which is the maximum number of threads the container can create to run on a Single instance of the servlet.
My question however is, is there a way to specify the number of instances of a servlet to be created? If yes, what is the purpose? The need for this may be to handle requests, when say a thread or threads running on the single instance somehow corrupt that servlet data or destroy() it - Redundancy purposes.
EDIT: Watch out ! As of Servlet Specification 2.4, interface
javax.servlet.SingleThreadModel is deprecated, with no direct replacement.
The specification is unclear as to whether containers should then create several instances of the same servlet, or always only a single instance.
From Servlet Specification 2.4 http://download.oracle.com/otndocs/jcp/servlet-2.4-fr-spec-oth-JSpec/
SRV.2.2 Number of Instances
The servlet declaration which is part of the deployment descriptor of
theWeb application containing the servlet, as described in Chapter
SRV.13, “Deployment Descriptor”, controls how the servlet container
provides instances of the servlet. For a servlet not hosted in a
distributed environment (the default), the servlet container must use
only one instance per servlet declaration. However, for a servlet
implementing the SingleThreadModel interface, the servlet container
may instantiate multiple instances to handle a heavy request load and
serialize requests to a particular instance.
In the case where a
servlet was deployed as part of an application marked in the
deployment descriptor as distributable, a container may have only one
instance per servlet declaration per Java Virtual Machine (JVMTM).
However, if the servlet in a distributable application implements the
SingleThreadModel interface, the container may instantiate multiple
instances of that servlet in each JVM of the container.
You can found in the document more information about Single Thread Model
