Architecture
of Oracle9i Advanced Queuing Sample
Table Of Contents
Imagine that there exists a Retail Shop which serves
various customers all over the world. This retail shop sells several different
products in several different categories. To do so, this retail shop has
tied with several product manufacturers which essentially form business
partners of this shop. These business partners include manufacturers of
Computers, Mobile Phones, Printers, Handheld Devices, etc...
Our Retail Shop has direct contact with these companies and sells their
product directly to customers.
Each of these manufacturers maintain their own databases
which is at a different physical location than our retail shop's database.
So, both of these databases will communicate to each other through Message
Propagation.
As the Retail Shop sells products all over the world,
the currency involved is different depending on the country the customer
belongs to. For our enterprise to serve all these customers effectively,
business transaction has to be done in the customers own currency. For
this, we will use the feature of Message Transformation provided in AQ.
For the delivery of purchased products there is a
Delivery module. This module gets automatically notified about the product
to be delivered through the use of PLSQL Notification.
Now, let us go into each of these in more detail.
Please refer to the block diagram provided ( Figure 1 ).
Figure 1
Whenever there is a change in a product price or a
new product has been manufactured, the manufacturer just updates its own
local Database. Through Message Propagation, this change will be
communicated to the Retail Shop's Database automatically and the tables
will be updated accordingly. For this, the sample will use the feature
of "Automatic Message Propagation" in AQ.
Now, when the customer enters the Retail Shop's web
site, he/she can see all the products that can be ordered. These products
can be from different manufacturers under different categories. The prices
will be displayed in US Dollars. When the user orders for a single or
multiple products, corresponding XML message will be generated and enqueued
in the Database Queue using IDAP Protocol and AQ Servlet. This entry will
be inserted in the Queue.
When a new order comes, an E-mail Notification will
be sent by the queue to the delivery module about the purchase. Through
a PLSQL notification, the required tables will be updated. During PLSQL
Notification, a Message Transformation will be applied and the price will
be converted in the User's local currency. The payment will be made by
the customer on delivery of the products. This will be simple as the entered
price is already converted to the users local currency.
No charges will be made for the delivery.
To see the database design used in the sample, please
refer to Figure 2.
Figure 2
The sample is divided into five layers namely; Presentation
Layer, Controller Layer, Event Manager layer, Business Layer and DataBase
Layer. You will find the layers similar to the MVC (Model-View-Controller)
Architecture. Let us look into these layers in more detail. Please refer
to the diagram provided (Figure 3)
Figure 3
Presentation Layer : This layer consists
entirely of JSP's. This is the layer which will actually interact with
the user. Every request will come from this layer and the response will
also be submitted to this layer. Each request from this layer is considered
an event. In other words, we can say that every click on a button ( in
a JSP ) generates an event which is then handled by the subsequent layers.
The JSP's here will not at any time interact directly with any of the
Java Classes, Beans or the underlying database. In essence, this layer
forms the view of the MVC Architecture.
Controller Layer : This is the layer from which
each and every request or response has to pass. This layer consists of
a single servlet namely, ControllerServlet.java and a XML file namely,
Control.xml. Control.xml is a XML file that consists information about
different parameters to be called on a particular event.
Event Manager Layer : This is the layer where
all the different type of events are managed. It consists of different
Java classes and XML files. All the methods in the Java files take the
HttpServletRequest object as one of the parameters. These methods call
the Business Layer with appropriate parameters which return some object
(Boolean, String, Vector or HashTable) depending on the event. This layer
then updates the HttpServletRequest and HttpSession object, if required.
Then the control is passed back to the ControllerServlet.java which forwards
the request to a JSP page
Business Layer : This Layer contains various
Business and Helper classes. All the classes in this layer will be stateless
and will not have any global variables associated. For every event that
can occur in this sample, a corresponding method will be contained in
the classes here. Almost every event generated by the customer/admin,
the flow will come to this layer as the actual processing will occur here.
This is the layer that will contain all the business methods for the sample.
The methods here will construct the database queries and pass it on to
the DataBase Layer. The methods in Business Layer will get the Vector
object from the DataBase Layer and will parse it and store the values
in a HashTable, Enumeration etc.. as and when required. These object then
will be returned to the Event Manager Classes which will act further on
them appropriately.
DataBase Layer : This layer will connect to
the DataBase physically. No other layer can connect to the database directly.
Every request pertaining to the database has to go through this layer.
For more information on various XML and Java Classes
contained in the layers, please refer to the comments/JavaDoc provided
in the files. For creating JavaDoc for the files, please refer to Install.html.
Revision history: May 29, 2002
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