Introduction

There are a variety of models for messaging in a distributed computing environment. The fundamental concept behind these models differs in the degree to which the two systems are synchronized. At one end, it is the synchronous model in which a system sends a message and waits for response. At the other end, it is the asynchronous model in which a system sends the message and continues processing (Fire-and-forget message exchange). Sending a message does not always require both systems to be up and ready at the same time. Participants in an asynchronous messaging system don't have to wait for a response from the recipient, because they can rely on the messaging infrastructure to ensure delivery. Asynchronous messaging is the strategy of choice for loosely coupled, Service-Oriented Architecture (SOA) because it overcomes the inherent limitations of remote communication, such as latency and unreliability.

The core of asynchronous messaging is Message-oriented middleware (MOM) like IBM MQSeries®. Let's look at how this works: To send a message, System A puts the message in the MOM using APIs exposed by MOM. System B, which wants to receive the message, can get the message from MOM using APIs exposed by MOM. If you don't have MOM libraries to use MOM APIs at your end, we can use a generic Web service, which exposes a method to put messages in MOM. The system which wants to send messages will need a Web service client. This client will be invoked when the system wants to send a message, and it will invoke the Web service and a message will be put into the MOM by the Web service.

Back to top

Configure WebSphere Application Server Version 6 for default messaging

To demonstrate the concept for this article, we need to configure WebSphere Application Server, version 6 (here after called WAS). To configure the WAS, perform the following steps:

• Create a bus
• Create a bus member
• Create a Destination
• Create a JMS connection factory
• Create a JMS queue
• Create a JMS activation specification

For detailed information on how to follow these steps, refer to the article "Deploying message-driven beans and JMS applications into the Service Integration Bus" in the Resources section.

Back to top

Using Web services to put messages into MOM

The Web service will have a method which, when invoked, will put a message into a queue. For the purpose of demonstration, we’ll use a text message, although the Web service can be written for any JMS message type. For information on how to write Java Web services, refer to the Redbook "WebSphere version 6 Web Services Handbook Development and Deployment", which is noted in the Resources section. Listing 1 shows the putMessage method of a sample Web service used for testing the code for this article.

        
public void putMessage(String message){
 try {
	Properties prop = new Properties();
	prop.put(InitialContext.INITIAL_CONTEXT_FACTORY,
		"com.ibm.websphere.naming.WsnInitialContextFactory");
	prop.put(InitialContext.PROVIDER_URL,
		"corbaloc:iiop:localhost:2809");
	InitialContext context = new InitialContext(prop);
			
	    //Do the lookup for Queue connection factory.	
	QueueConnectionFactory 
	  factory =(QueueConnectionFactory)context.lookup("JMS/MyQueue_CF");
			
		//Do the lookup for Queue. 	
	Destination queue = (Destination) context.lookup("JMS/queue");
			
		//Create connection and start it.	
	Connection connection = factory.createConnection();
	connection.start();
	System.out.println("connection created");
			
		//Create session and message producer.	
	Session session = connection.createSession(false,Session.AUTO_ACKNOWLEDGE);
	MessageProducer producer=session.createProducer(queue);
	System.out.println("producer created");
	System.out.println(producer.getDestination().toString());
			
		//Prepare the text message.	
	TextMessage msg=session.createTextMessage();
	msg.setText(message);
			
	    //Send the message.	
		producer.send( msg);
	    System.out.println("sent message : "+msg.getText());
		        
   } catch (Exception e) {
	e.printStackTrace();
  }
}

      

The putMessage method looks for a Connection Factory, JMS Destination objects into JNDI. Then it creates the connection, session and finally a message producer for the JMS destination, puts the text message into the queue.

Back to top

Configuring the database

The database configuration is required to automatically invoke the Web service client. This can be done in a number of ways. For example, you could write a Trigger and Trigger calling User Defined Function, or write a Trigger and Trigger calling a Java Stored Procedure. For the purpose of demonstration we use Trigger and Java Stored Procedure combination and DB2 database. Perform the following steps to configure your database.

Create a sample table

Run the following SQL command to create a table:

        
		CREATE TABLE customer 
(
	pkey INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START 
        WITH 1, INCREMENT BY 1, NO CACHE ) PRIMARY KEY,
	fname		VARCHAR(20),
	lname		VARCHAR(20),
	ccode		VARCHAR(10)
);
		
        

Create a Java SP

This Java Stored Procedure (Java SP) is the key behind the concept of this article. The Java class which will be invoked when this Java SP is called, will have code to invoke the Web service. Run the following SQL command to create a Java SP.

        
CREATE PROCEDURE MyPROCEDURE ( IN var0 INTEGER,IN var1 VARCHAR(20) )
    SPECIFIC SQL060622110835012
    DYNAMIC RESULT SETS 1
    NOT DETERMINISTIC
    LANGUAGE Java
    EXTERNAL NAME 'MyPROCEDURE.invokeWS'
    FENCED
    THREADSAFE
    PARAMETER STYLE JAVA
		

The below code listing shows the MyPROCEDURE Java class. This class has a method called invokeWS. This method takes three parameters, the primary key, the action performed on the table (create, update, delete) and a result set. I have used Axis APIs to write the Web service client code in this method. For compiling and running this class, make sure Axis jars are in your class path.

        
import java.sql.*;
import java.io.FileOutputStream;
import java.io.PrintStream;
import javax.xml.rpc.ServiceFactory;
import javax.xml.rpc.Service;
import javax.xml.rpc.Call;
import javax.xml.rpc.ParameterMode;
import javax.xml.namespace.QName;

public class MyPROCEDURE
{
  public static void invokeWS ( int var0, String var1, ResultSet[] rs1 )
  throws SQLException, Exception
   {
      try{
	  //create service factory
	    
	    ServiceFactory factory = ServiceFactory.newInstance();
   // define qnames
	    
	   String targetNamespace = "http://asyncmessage.ibm.com";
	   QName serviceName = new QName(targetNamespace,"AsynchronousMessageWSService");
	   QName portName = new QName(targetNamespace,"AsynchronousMessageWS");
	   QName operationName = new QName(targetNamespace,"putMessage");
	    
  // create service
	    Service service = factory.createService(serviceName);
	    
  // create call
	  Call call = service.createCall();
	    
  // set port and operation name
	  call.setPortTypeName(portName);
	  call.setOperationName(operationName);
	    
  // add parameters
	  call.addParameter("message", 
	  new QName(targetNamespace,"string"),ParameterMode.IN);
	  call.setReturnType(new QName("",""));
	    
  // set end point address
	   call.setTargetEndpointAddress("http://localhost:9080/AsyncMessagingSamples
	    /service/AsynchronousMessageWS");
	           
  // invoke the remote web service
	    call.invoke(new Object[]
	    { "Message from DB2 : a row with primary key"+var0+" is "+var1+"d"});
	          
       }catch(Exception e)
     {
        try{
                	      
          FileOutputStream fout=new FileOutputStream("errors.txt");
           e.printStackTrace(new PrintStream(fout));
                              
		}catch(Exception e1){}
      }
   }
}

	

Create Triggers on the sample table

In the sample code, we have created three Triggers on the customer table for Insert, Update, and Delete. This is used, for example, whenever a row is inserted, updated or deleted in the customer table. When one of these things occurs, Triggers will be executed. These Triggers will then call the Java SP, which in turns invoke the invokeWS method. Run the following SQL command to create Triggers. Let’s see how this works:

        
//Trigger for row insertion
	CREATE TRIGGER event_create 
	AFTER INSERT ON CUSTOMER REFERENCING NEW AS N  
	FOR EACH ROW MODE DB2SQL 
	call MYPROCEDURE(N.pkey,'create') ;

//Trigger for row updation
	REATE TRIGGER event_udpate 
	AFTER UPDATE ON CUSTOMER REFERENCING NEW AS N  
    FOR EACH ROW MODE DB2SQL 
	call MYPROCEDURE(N.pkey,'update') ;

//Trigger for row deletion 
	CREATE TRIGGER event_delete 
	AFTER DELETE ON CUSTOMER REFERENCING OLD AS O
	FOR EACH ROW MODE DB2SQL 
	call MYPROCEDURE(N.pkey,'delete') ;

		

Back to top

Create a MDB

To complete the scenario, we need to create a Message Driven Bean (MDB). This MDB will subscribe to the Queue, in which our Web service will put the messages. For detailed information on how to configure the MDB, refer to the article "Deploying message-driven beans and JMS applications into the Service Integration Bus", which you can find in the Resources section. Listing 6 shows snippets from ibm-ejb-jar-bnd.xmi file and the onMessage method of sample MDB used for this article.

Note: some parts of ibm-ejb-jar-bnd.xmi file have been truncated for easy reading and important attributes have been marked bold.

        
.........................................................
<ejbBindings .....
	activationSpecJndiName="eis/MyQueue_activation_spec" destinationJndiName="JMS/queue">
	..........................................................
	<resRefBindings ......... jndiName="JMS/MyQueue_CF">
	..........................................................
	<resRefBindings ..... jndiName="JMS/queue">
	...........................................................
</ejbBindings>
		
		
public void onMessage (javax.jms.Message msg)
	{
           try {		
                 System.out.println("***********************************");
		 System.out.println("***********************************");
                 System.out.println("***"+((TextMessage)msg).getText()+"***");
		 System.out.println("***********************************");
		 System.out.println("***********************************");
               } catch (JMSException e) 
                       {
			 // TODO Auto-generated catch block
			    e.printStackTrace();
		   	}
	}

		

Back to top

Putting it all together

We've completed the required setup. Deploy the web service in WebSphere Application Server. Now whenever we create, update or delete a row in a customer table, a message will be written in SystemOut.log file of WebSphere Application Serverby MDB. If you create a row with primary key 100 in a customer table, the message will look like "Message from DB2: a row with primary key 100 is created".

Back to top

Conclusion

In this article, we learned how we can enable asynchronous messaging over HTTP using Web services. The major benefit of this approach is that this is platform and language independent and it gives you freedom from writing JMS clients to send messages to MOM.

Author's note

The author would like to thank Krishnakumar Balachandar (KK), WebSphere Community Edition/Geronimo L3 Support Lead, Shishir Narain, WebSphere Partner Gateway development, and Shaji Vaidyan, WebSphere Adapter for JDBC, Support and Development for their reviews and comments on this article.

Back to top

Download

Information about download methods

Resources

• "Deploying message-driven beans and JMS applications into the Service Integration Bus" (developerWorks, April 2005) shows how WebSphere Application Server V6 makes it easy to build message buses and deploy applications, and how IBM Rational®Application Developer enables developers to create and test JMS applications that communicate using the message bus.
  
  
• "Solve common problems with DB2 UDB Java stored procedures" (developerWorks, October 2005) shows working examples and common solutions to help you get up and running, problem free, with your own Java routines.
  
  
• The IBM Rebook "WebSphere Version 6 Web Services Handbook Development and Deployment" describes the concepts of Web services from various perspectives.
  
  

About the author

Comments (Undergoing maintenance)

Back to top

Trademarks  |  My developerWorks terms and conditions

Table of contents

• Introduction
• Configure WebSphere Application Server Version 6 for default messaging
• Using Web services to put messages into MOM
• Configuring the database
• Create a MDB
• Putting it all together
• Conclusion
• Download
• Resources
• About the author
• Comments

Next steps from IBM

• Try: DB2 Enterprise
• Demo: DB2 serving ATOM feed
• Webcast: A smarter way to successful SOA - Information as a trusted strategic asset
• Briefing: Information on Demand
• Buy: DB2 Enterprise

My developerWorks community

Dig deeper into SOA and Web services on developerWorks

Rate a product. Write a review.

Write a review for Rational products today!

Special offers