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JBridge: Certification Question Of The Day
JBridge Home >> Certification Questions >> Question for Friday May 23rd 2003 Friday May 23rd 2003
Identify which of the following statements about servlet containers are false (2 correct answers).

A A servlet container that does not support clustering will still start even if the deployment descriptor web.xml contains the <distributable/> marker.
B Sessions for a web application can be distributed across several JVMs, but any one session must remain attached to a single JVM.
C All objects placed in a session must invariably implement java.io.Serializable.
D There are four standard architectures relating to servlet containers and their distributable qualities.
E Session migration (if supported) is guaranteed to occur between user requests.
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The Answer

Answers B and C are the correct answers, as they are false statements. Both statements are in fact true for some (but not all) levels of servlet container architecture. Answer B is true for servlet containers which support clustering, but not session migration or session failover. Answer C is true for servlet containers which DO support session migration (but it's not compulsory to serialize session data for lesser containers).
It is true that a servlet container not supporting clustering will still start even when tagged as distributable. I have tested this against the standalone version of Tomcat.
There are four standard distributable architectures:

  1. Level 1 - no clustering.
  2. Level 2 - clustering, no session migration, no session failover.
  3. Level 3 - clustering, session migration, no session failover.
  4. Level 4 - clustering, session migration, session failover.
And finally, where session migration is supported, the servlet specification does guarantee that session migration will occur between the processing of user requests.

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