JMS Chat Sample Application 

Table of Contents

• Overview of the Sample Application 
• User Notes with Screen Shots 
• Installation and Configuration 
• Description of Sample Files 

JMS (Java Messaging Service) is a strategic technology for J2EE. JMS works in concert with other technologies to provide reliable, asynchronous communication between components in a distributed computing environment. Enterprise messaging is now recognized as an essential mechanism for building enterprise applications. By combining Java technology with enterprise messaging, the JMS API provides a new, powerful tool for solving enterprise computing problems. 

The OC4J JMS provider allows the user to choose either in-memory or file system based message persistence. This sample application demonstrates the use of in-memory queues which are configured in jms.xml.

An MDB (Message Driven Bean) is a stateless, server-side, transaction-aware component that is driven by a Java message (javax.jms.Message). It is invoked by the EJB Container when a message is received from a JMS Queue or Topic. It acts as a simple message listener. 

This sample application demonstrates the features and usage of in-memory JMS queues and MDB. The sample uses the scenario of a Chat Application for demonstrating these features. Using this application, a user can login to a Chat Room and send/receive messages to/from other registered users. 
 

User Notes with Screen Shots

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The sample application consists to two components. They are described as follows :
 

• Server Component : This component is an ear file and runs on OC4J. It constitutes of two servlets (for receiving and sending messages) and an MDB (for listening to the enqueued messages). Any operation on the queue (single receiver) or the topic (multiple receiver) can be done through the classes present in this component.

 
• Client Component : This component is a jar file and constitutes of Java classes that generate a swing interface to help the logged in user to chat with other registered users. When the user first starts the application, then he/she will see the following screen

 


Through this window, the user specifies where the Chat Server is running. The user also specifies the ChatID that he/she is going to use. If you have previously logged into the application, then the application will remember your ChatID. In this case, please select I am an existing user. The application will remember the ChatID until the OC4J server is restarted. Please note that the UI of the window may change according to the system settings. 
After he/she has successfully registered the ChatID on the Chat Server, then the following window will appear.
 




The User will now chat through this window. All the messages from other users will appear on the top TextArea. The User can send a message to other users by typing it in the bottom TextArea and then pressing the Send button or by pressing the Return key on the keyboard.
The application also stores offline messages. This means that if a registered client is not active and there is some chatting going on during this time, then this user will receive all the messages when he/she logs in the next time. The messages will be stored in the server till either all the subscribers have received it or the server restarts.

Please refer to Installing the sample for step-by-step instructions on extracting the files, deploying and running the application successfully. 
 

Description of Sample Files

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The directory structure of the deliverable JMSChatSample.jar is as shown below.  Please note that the important files for the JMS functionality are located on the server; namely the files SendMessage.java, GetMessage.java, ChatSubscriber.java and ListenerMBDBean.java.
 

Directory	Files	Description
ChatSample\doc	Readme.html	This file
	Install.html	This file has instructions required to install and deploy the sample application.
ChatSample\server\Chat\src\oracle\otnsamples\oc4jjms	SendMessage.java	This Servlet is used by the Chat Client to send the message.
	GetMessage.java	This Servlet is used by the Chat Client to receive a message.
	ChatSubscriber.java	This Java class has the important methods for adding a subscriber and dequeing the message. The methods in this class are used by the GetMessage.java servlet.
ChatSample\server\Chat\src\oracle\otnsamples\oc4jjms\impl	ListenerMDBBean.java	This MDB listens to the messages sent by the Chat Clients.
ChatSample\client\src\oracle\otnsamples\oc4jjms	All Java Files	These files together constitute the Client Swing Application to access the Chat Server.

Please enter your comments about this sample in the OTN Sample Code Discussion Forum.