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xiaolin yu

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since Nov 17, 2002
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Recent posts by xiaolin yu

The answer of the following question maybe is d. Could anybody give me some explanation? Thanks!!
When designing a primary key generator for your J2EE application, which of the following would be the BEST option?
a) Depend on database specific key generation support, accessible through stored procedure
b) Build custom key generation engine deployed to database, accessible through stored procedure
c) Use a local primary key generation algorithm to eliminate synchronization delays
d) Use local management and delivery of centrally generated primary keys
Single Select - Please select the best answer (one and only one choice must be selected).
WebSphere Application Server provides a service that transfers data or events among WebSphere Application Server servers. The service is called WebSphere Internal Replication, or replication for short.
The replication service transfers both J2EE application data and any internal data used to maintain the application data among WebSphere run-time processes in a cluster of application servers.
Currently, the Web container in WebSphere Application Server leverages replication.
The replication service can replicate HttpSession data among processes and retrieve the HttpSession if the process that currently maintains the HttpSession fails. Using replication for HttpSession failover provides a potentially lower cost and more easily administrable alternative to storing HttpSession in a relational database. Further, the service can distribute across a WebSphere cluster information on invalid data and actual cached data maintained by a Web container's dynamic caching.
URL link:
Really don't know the answer, please give me a help. Thanks in advance!!
While testing a Session bean configured with "Bean Managed", a developer discovers that a TransactionRolledBackException is being thrown by a call to a method on an Entity Bean. The Session bean, prior to calling the method, explicitly started the transaction. Possible causes for the exception are that the:
a) entity bean method is throwing a checked exception.
b) entity bean method is throwing an un-checked exception.
c) entity bean is configured with a transaction attribute of "Not Supported".
d) entity bean method is throwing an exception and the entity bean is configured with a transaction attribute of "Requires New"
Multiple Select - Please select all of the correct answers (this question has 2 correct choices).
The answer of the question below is d. Could anybody tell me why?
Thanks in advance.
A Servlet must perform 3 operations that are independent of one another. They are time consuming with each operation consuming about 10
msec of CPU. The Servlet's response depends on the completion of all three operations. The developer decides to perform each operation
on a separate worker thread to run them concurrently. Which of the following describe important parts of this implementation?

a) The Servlet should implement MultiThreadModel.
b) The Servlet should implement SingleThreadModel.
c) Access to the HttpSession must be synchronized.
d) The worker threads must not write to the ServletOutputStream.
e) The worker threads must not read from the ServletInputStream.
I think to know why and how Singleton works, we need to know Java Virtual Machine structure. I don't know it either. I only know classes run in the same JVM calling Singleton class work on the same instance.
It provides a function similar to database. For example, we can use Singleton as the service locator to cache the class instance.
Front Controller is the controller processes the Http request. Web Controller is the business delegate in web tier. EJB Controller is the session facade in EJB tier.
The reason you feel confused is that Sun used the command pattern to hide the transfer objects.
I spent a lot of time to analysis the Pet Store example. Sun should give us detailed UML pictures and code(JSP included).
Hi, Chris:
Thanks for your replay, but I think what I thought will affect the architecture a little bit.
So I think to use a log out function which let users log out the account by clicking the "log out" button or the system log out the user account automatically in 15 minutes from the time the user log in. This will be better.
Please give me some suggestion.
Your message was edited since you quoted content from the actual assignment. Please read our policy on SCEA questions and refrain from discussing actual assignment issues.
Thank You!

[ August 13, 2003: Message edited by: Ajith Kallambella ]
From weblogic:
"Local interfaces allow enterprise javabeans to work together within the same EJB container using different semantics and execution contexts. The EJBs are usually co-located within the same EJB container and execute within the same Java Virtual Machine (JVM)."
Is it possible that web container and EJB container use the same JVM? If it could be, then servlet can call EJB methods from local interface without network headache. Is that right?
[ January 03, 2003: Message edited by: xiaolin yu ]
Sorry for posting original words. I think I have got the answer.
Thanks a lot for your help. It depends on the firewall filtering configuration.
I have another question: in the background there is a requriement about "Frequent Flyer Mileage System"
--"..., but would like to have the content available to the customer using the web and the travel agent using an application. This system was developed using Perl, HTML, CGI and an Oracle database."
Should we get content of "Frequent Flyer Mileage System" from EJB tier or not?
Thanks again!
Should the FBN system use the firewall? If it does, then travel agent could not communicate with the EJB tier directly by RMI. Because the RMI-IIOP could not break through the firewall. The only possible way is to use HTTP. Is that possible that travel agent inside the firewall?
It will be retired in 2003 and it's the reason why he give us 2000 free vouchers. Right now the companies are using at least J2ee 1.3 version. So the Websphere application server 5.0 is the best choice in IBM's products. Don't spend any time to prepare the certification tests of the old version, it will give you nothing except a useless IBM certificate. WebLogic application server 7.0 is the better product, so it's certificate is better and you can take it right now. IBM spend more time and energy on certification tests than on upgrading their products.
I passed IBM 141, 157 and 158 mock tests 5 days ago, but still has not received e-mail notification. I am not sure if it was too late.