In an enterprise application, clients are always required to
interact with various service components, such as Enterprise Javabeans (EJB)
and Java Message Service (JMS) as they provide the business methods to run the
service. This is possible only after locating a business service (referred as
a lookup operation). J2EE uses the JNDI tree to lookup, access and invoke business
services on passing a unique registered JNDI name. If the service is used by
various clients, then the code for looking up the object gets duplicated in
various forms which makes it difficult to maintain the application.
The Service Locator Design Pattern solves this issue by abstracting the complexities
and network dependencies into a single Service Locator class. This service layer
pattern can be used for storing lookup values for all services and provide it
on request. A caching mechanism can also be incorporated within the service
to enhance performance as the JNDI lookup is made once only.
Application Overview
This application demonstrates the implementation of Service
Locator design pattern. In an enterprise application, generally there is a module
for getting the feedback from the customer. The sample application targets this
scenario to explain how to implement the Service Locator pattern.
In this application, the customer provides the feedback with his/her name and
e-mail ID. Using an Entity bean (Feedback), the application first
enters the feedback in the database table. After this is successfully executed,
the information is entered in a queue (MailQueue). The lookup for
the EJB, QueueConnectionFactory and the Queue is done through a Service Locator
class. An MDB (MailMDB) is registered to listen to the queue. The
MDB is asynchronously invoked and sends an e-mail to the customer thanking for
the feedback.
The objects are also cached within the Service Locator class which improves
performance as the lookup is done only once during the first request and not
for subsequent requests.
The following class diagram shows the important classes in the
Service Locator pattern.
The following sequence diagram depicts the interactions in this sample application.
Software Requirements
Following is the list of software's required for configuring
and running this sample application.
Directory where OC4J is installed. For example. D:\oc4j10g
<JAVA_HOME>
Directory where JAVA is installed
<ANT_HOME>
Directory where Apache Ant is
installed
<SAMPLE_HOME>
The directory where the sample
application is extracted.
Configuring the
Application
Unzip the provided ServiceLocator.zip. This creates
ServiceLocator folder with all the source files.
We will refer to this folder as <SAMPLE_HOME>.
Install the database table. Connect to the SCOTT
user in the database and run the following command
SQL> @<SAMPLE_HOME>/sql/Install.sql
Edit <SAMPLE_HOME>/config/mail.properties
file in your favorite editor. Change the value of SMTPServer to connect
to your mail server.
To setup the database connection, edit the data-sources.xml
file in the <SAMPLE_HOME>\src\META-INF directory and edit
the following connection information within the <data-source>...</data-source>
tags.
Replace <dbHostName>:<dbPort>:<dbSID> in the
url, with your database values and save the file. If required, replace the
username and password attributes. where,
dbHostName
=
hostname of the machine
where Oracle database is running
dbPort
=
port on the host machine
on which the database listener is listening
dbSID
=
SID of the database
Deploying and Running
the Application
This section describes the steps required
in deploying this application to the Standalone OC4J using ANT Tool and running
using the browser.
Note:
Make sure that the environment variables[<JAVA_HOME>, <ANT_HOME>/bin
in the PATH;, <JAVA_HOME>/bin in the PATH] have been set before proceeding
further. For more information on how to setup these environment variables, please
refer environment set up readme
document.
Edit <OC4J_HOME>/j2ee/home/config/jms.xml
in your favorite XML editor. Add the following lines under the <jms-server>
tag.
Ensure that OC4J is up and running. To start the OC4J
server, navigate to <OC4J_HOME>/j2ee/home and execute
the following command,
> java -jar oc4j.jar
Open the <SAMPLE_HOME>/config/server.properties
in a text editor. Change the following parameters to with your OC4J details.
OC4J_HOME
=
Folder where OC4J is installed. Ex: D:\oc4j10g
OC4J_HOST
=
Machine name or IP address on which OC4J is running
OC4J_PORT
=
ORMI port on which your OC4J listens for ORMI
requests
OC4J_USERNAME
=
User name of OC4J server, default is admin.
OC4J_PASSWORD
=
Password of OC4J server.
Build and deploy the EAR file
using ANT. From <SAMPLE_HOME> directory, execute the
command,
> ant
Open your favorite browser and access the sample application,
using the following URL,
http://hostName:port/locator/Feedback.jsp
where,
<host_name> is the machine on which OC4J is running and <port>
is Port in which the OC4J server listens to HTTP requests. By default OC4J
listens for HTTP requests in port # 8888
Example: http://localhost:8888/locator/Feedback.jsp
Sample Application
Files
This section provides a tabular listing of the sample application
files, along with their respective directory locations and a description of
what they do in the overall scheme of the application.
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