The best and most popular technique of specifying such
configuration information is to define it in a XML file. The
Trader object can then parse this XML file and load the
appropriate configuration information to look for the
appropriate component instance form the class libraries provided
to its access. As the Trader object demands a particular set of
information that should always be present in the configuration
XML file, it is a good strategy to define an XML Schema for the
same.
We start with the XML Schema definition for the Trader
configuration.
Listing 1 presents the XML schema that we came up
with.
View Listing 1
Note that the Schema defines the following items.
- The root element is <component-definition> .
- The <component> element has a required attribute "name".
- The <component> element has required child elements
<inteface> , <instance> and <service-type>.
A sample XML file following the trader.xsd Schema definition may
look like the following in listing 2.
View Listing 2
This configuration XML file defines a component named "Account".
The component implementation follows an interface definition in
sam.services.IAccount. Also, the concrete implementation of that
interface is sam.ejb.AccountHome and the Trader object should
create an instance of the AccountHome object and return it to
the client. The <service-type> defined has a value "ejb" which
indicates the Trader object that the component requested is an
EJB component.
Hold on a minute. How does the Trader know where to look for
this EJB component! Yes, there is a clue. We need to define
it somewhere. We decide to define the service configuration in a
separate configuration file. Listing 3 shows a sample service
configuration file.
View Listing 3
This XML file provides the required information for the EJB
lookup for the specified object. Notice that, the component in
question is identified with the unique name attached to them. As
you can see, this configuration file can be used to define other
configuration parameters that a particular service may need to
know about. For example, for a normal Java implementation of the
Account component, you may decide to supply the database
connection information. Of course, the Trader object
implementation grows with such requirements in place. However,
it might be useful to employ some helper classes to achieve the
configuration settings on the component instance.
In the next section, we take a closer look at parsing and
caching the information provided in the configuration files in
order to develop a Trader object.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
