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Along huang

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Recent posts by Along huang

I am developing a SMS(short message) system, it relate to send millions of messages to user's mobile phones, so I use JMS to keep the messages temporaryly, and the system must load data from database into JMS Server group by group.

When first group messages is nearly consumed over, the system must detect the status of JMS server(how many messages remain), so that it can load second group messages in time.

The problem is that how can I know how many messages remain in Queue?

Along
If a comapny's HR manager interview with me and require me offering something to certify my cerificates, but I can't show something except the paper.

I want to how if somewhere HR department can find my certificates conveniently, such website?

best regards
Along
I just read through the instruction two times, and think of the below problems about the Mileage System:

1. How is the table schema in Mileage System?
2. What is the awarding regulation?
3. Do it use the same database as the new system? If the database is different, should the transaction implement two-phase committing?

Could anyone give me any proposals?

best regards
[ May 24, 2005: Message edited by: Along huang ]
According to some stuffs, the 2-tier architecture has some faults, but following two confuse me:
1) Potential network bottleneck;
2) poor scalability. As the business is tightly coupled with data store.

To 1), I can't understand at all. Why do there exist this problem? In comparison with the 3-tier architecture, here is no any special case when clients connect server, whatever you use 2-tier or 3-tier, the network traffic from client to server is equivalent.

as to 2), it make more confusion to me, in terms of the the book Sun Certified Enterprise Architect Study Guide, here are two ways to improve the scalability of system, first is Vertical, such as increasing CPU and momery, second is horizontal, such as cluster technique.
But, in 2-tier, it can be added CPU or hot backup server to improve performance, so as to achieve the goal of scalability.

Who can give me a sound explanation? I will thanks a lot

best regards

[ April 01, 2005: Message edited by: Along huang ]
[ April 01, 2005: Message edited by: Along huang ]
I want to know how to implement this functionality in coding sight, both net-address and document are appropriate.

Thank you in advanced!

Best regards
[ March 31, 2005: Message edited by: Along huang ]
Thank you for your direction!

In another scenario, during a transaction processing, the application suddenly crash.

In this case, if the transcation will be rocked back? if ture, what system process it? it is obvious that it is not application server because it have crashed. The only answer is database server, is it?

best regards
Ravi,

I am sorry, I don't understand what J2EE client container mean. or could you explain it?

best regards
In a mock question:
When a call is made to a single-entity find method in an entity bean, the
ObjectNotFoundException is thrown indicating that the requested entity was not found.
What happens to the transaction?(Select 1 correct choice)
a) It is automatically rolled back since it is an application exception.
b) It is not automatically rolled back since it is a system exception.
c) It is not automatically rolled back since it is an application exception.
d) It is automatically rolled back since it is a system exception.
e) It may or may not automatically rollback based on container specific implementation.

The correct answer is c).

Here are two problem confusing me:

1. How can I know a exception is System exception or Application exception? As ObjectNotFoundException, I really don't know it belong to which type.

2. In a transaction, does it really not roll back automatically when meeting a application exception? what happen when it meeting a SQL exception that is defind by developer(such as a exception included in store procedure)?

best regards
I think that it is possible, but whether it may be used or not due to the architecture of your application. In the architecture "Swing + EJB + Database", I strongly recommend that you don't use FrontController, it will make more complex to introduce it, I perfer to use a Proxy.

But in the architecture "Swing + web + EJB + Database", it is appropriate to use FrontController as all client request data must be translate into Stream. This FrontController will communicate with another FrontController locating web tier.

best regards
[ March 24, 2005: Message edited by: Along huang ]
Hi, Ravi,

Does this mean you planning on using Java webstart to connect the EJB container and the Swing application?



Sure is, I perfer that client swing directly access EJB overleaping web tier, but the precondition is firewall don't become a barrier.

best regards
I meet the question:
What is the difference between composite aggregation and normal aggregation.
a) Aggregation defines a part of relationship but both objects can exist independently.However, with composite aggregation if one part is removed, then the other part will also be removed. Think of a plane the wings have a composite aggregation relationship with the body of the plane.
b) Composite Aggregation defines a part of relationship but both objects can exist independently. However, with aggregation if one part is removed then the other part will be removed. Think of a plane, the wings have an aggregation relationship with the body of the plane.

The correct answer is a), but I can't fullly comprehend the concept, where can I find more stuff on this subject?

thanks in advanced
hi,Ravi,

I had adopted Java Webstart framework in my past project, which use Swing + WebServer + AppServer + Database structure.

I found that it is very boring to use this framework, as client tier must communicate with web tier over Socket, it means that you have to modify some classes of Structs framework so that web tier can receive and send stream data to client tier, it result in losing the integrality of the Structs.

So, I don't enjoy this kind of architecture, I prefer to the two architecture as below:
1) thick client: Swing + AppServer(EJB) + Database (i.e. java webstart, it needs also to bypass firewall)
2) thin client: Browser(IE) + WebServer + AppServer + Database

How is your Java Webstart structure? it is like mine?

I never try the Tunnelling technique so I don't know the exact performance.
hi Lim, first, thank you for reply!

As far as know, a technique named tunnelling can solve the problem, which use http protocol and 80 port. But, one book I had looked recommend that people don't use this technique commonly as its terrible performance.

best regards
it is a mock quiz as below:
19. Which two of the following statements correctly describe the Publish/Subscribe
Messaging model and the Point-To-Point Messaging model respectively?(Select 2 correct
choices)
a) Publish/Subscribe Messaging is a message queue system.
b) Publish/Subscribe Messaging = One sender and one receiver.
c) Point-To-Point Messaging = N senders and one receiver.
d) Publish/Subscribe Messaging = 1 sender and n receivers.
e) Point-To-Point Messaging is a message queue system.
f) Point-To-Point Messaging = One sender and one receiver.

the answer is d) and f).

Why e) is incorrect? who can get me a explanation?

Best regards