Object serialized many times - code in finalizer runs multiple times

Question

          Using on Solaris:
          Weblogic Version 5.1 sp 8
          JDK version: java full version "1.3.0-RC"
          Clustering with:
          weblogic.httpd.session.persistentStoreType=replicated
          I have an object that stores information in a linkedList member.
          The first time a user passes through a servlet, one of these
          objects is created for them. It is stored in session.
          The object implements serializeable. Upon finalization, this
          object is supposed to flush its data once and only once to a log file.
          The object's constructor runs once. It is set and retrieved once from HttpSession.
          As WebLogic shuts down, the object is then serialized and deserialized many times.
          The finalizer of this object then runs many times as weblogic shuts down (17 or
          so times), duplicating the logging of the information
          each time. Each time, doing a this.toString() in the finalizer prints out a different
          object reference.
          I tried setting and incrementing both a static and
          instance level variable and printing them out during finalization. The static
          class variable gets incremented as you would expect, the non-static instance variable
          is always incremented from 0 to 1 each time a finalizer runs. So there is no linkage
          between the instances at the non-static level.
          We are using clustering (though only one app server was running during the test),
          JSPs, servlets, etc.
          We need to have the finalizer for each original instance of the object execute
          its logging functionality once and only once regardless of serialization/deserialization.
          Any ideas as to how this can be done or another place to put the logging code
          so it will be executed after a user session ends?
          Thanks!
          Peter
          

Answer 1

Using finalization is a very bad idea, both from the performance and program
          correctness points of view.
          I think you can look into using javax.servlet.http.SessionBindingListener
          (valueUnbound(event) will be called when object is unbound from the
          HttpSession) instead.
          Peter Gluck <[email protected]> wrote:
          > ---------------------------
          > Using on Solaris:
          > Weblogic Version 5.1 sp 8
          > JDK version: java full version "1.3.0-RC"
          > Clustering with:
          > weblogic.httpd.session.persistentStoreType=replicated
          > -------------------------
          > I have an object that stores information in a linkedList member.
          > The first time a user passes through a servlet, one of these
          > objects is created for them. It is stored in session.
          > The object implements serializeable. Upon finalization, this
          > object is supposed to flush its data once and only once to a log file.
          > The object's constructor runs once. It is set and retrieved once from HttpSession.
          > As WebLogic shuts down, the object is then serialized and deserialized many times.
          > The finalizer of this object then runs many times as weblogic shuts down (17 or
          > so times), duplicating the logging of the information
          > each time. Each time, doing a this.toString() in the finalizer prints out a different
          > object reference.
          > I tried setting and incrementing both a static and
          > instance level variable and printing them out during finalization. The static
          > class variable gets incremented as you would expect, the non-static instance variable
          > is always incremented from 0 to 1 each time a finalizer runs. So there is no linkage
          > between the instances at the non-static level.
          > We are using clustering (though only one app server was running during the test),
          > JSPs, servlets, etc.
          > We need to have the finalizer for each original instance of the object execute
          > its logging functionality once and only once regardless of serialization/deserialization.
          > Any ideas as to how this can be done or another place to put the logging code
          > so it will be executed after a user session ends?
          > Thanks!
          > Peter
          Dimitri