JMS Messagen Store and JMS Message Processor Behavior - WSO2 ESB - Part 3

So why did we meet the EVIL in the my last blog post? Why? yes that is the main reason behind this blog series!!

Now we have to take a deep breath before we dive into the WSO2 ESB and see why this has happened!!

If you carefully study the illustration shown in Figure 1, You will understand whats goes wrong ;)

Figure 1

Anyway, let me take some more time to explain little bit further.
Client sends message to Proxy. "Message Store" persist the message in the message store(JMS Queue). "Message Store" does not persist the message as it is in the JMS Queue. it serializes the message and other information into java serialized object and put it into JMS Queue.When "Message Processor" processes the message, it pulls Messages from JMS Queue and deserializes the java serialized object to further process.

So why did we encounter some exception and other problems in issue 1?
When Message Processor Pull the message from JMS Queue and try to deserialize, Deserilzation process fails since the fetched message is not Serialized by Message Store.

So is that possible to put message into Message Stores's "JMS Queue" ?? NO it is not possible!!!


So whats wrong with Issue 2?
Different JMS listener dose not know how to deserialize the message that fetched from JMS Queue(Message Store)!

Conclusion   

Messages that are put into "JMS Queue" by "Message Store" are can be read only by "Message Processor" and "Message Processor" only capable of understanding the messages that are put by "Message Store".





  

Hello JAX-RS

In my last post i have given a brief  introduction to JAX-RS. Before look into this further It would be great if we do a hands on session to understand the usage and development procedure.

For the change, I will start with “Hello JAX-RS” instant of “Hello World”!!!!

In order to do this i am using maven as a builder, Tomcat Server as application server and Idea intellij as IDE. Most importantly I am using jersey 1.17.1 as the JAX-RS implementation.

First of all we have to create a web application project. This task can be achieved by maven.

mvn archetype:generate -DgroupId=com.area51.rest -DartifactId=RESTfulExample -DarchetypeArtifactId=maven-archetype-webapp -DinteractiveMode=false

After project created by maven, the folder structure looks like. If you see carefully "java" folder is not there in the folder structure.

Folder Structure

Thu i have manually added a folder under src/main/java and ran mvn idea:idea (if you are using eclipse use mvn idea:idea)

I have share the complete project here 

Given pom.xml I have added the  dependency for  jersy and set the source as java 1.6.
HelloJaxRsService.java is the implementation for "Hello JAX - RS"demonstration.

If you carefully study into the code that i have given, you can understand that "@Path("/hello")" annotation indicate the context of the class "HelloJaxRsService.java". "@GET" indicate the methods classify the methods as GET request method (HTTP vocabulary of request operation).  @Path("world/{param}") annotation is a resource in the "hello" context with the parameter.


Okay, Lets up and run this code.

First of all! compile the code using maven!,  get the "war" file! and configure the apache tomacat server with it.

In this example, web request from “projectURL/rest/hello/” will match to “HelloJaxRsService“, via @Path("/hello").

http://localhost:9000/RESTfulExample/rest/hello/world/human request hits the hello context and world resource.

http://localhost:9000/RESTfulExample/rest/hello/home/Vanjikumaran request hits the hello context and home resource.

Java API for RESTful Services

Java API for RESTful Services (JAX-RS)

JAX-RS: Java API for RESTful Web Services is a Java API that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern. Furthermore JAX-RS uses annotations to simplify the development and deployment of web service clients and endpoints.

To Understand further about JAX-RS refer the document provided by oracle[1] which contain compressible information about JAX-RS.


You can find various implementation that are available in industry and well known implementation are

1) Apache CXF - an open source Web service framework provided by Apache Software Foundation.
2) Jersey - an implementation from Oracle.
3) ESTeasy - an implementation from JBoss.
4) Apache Wink, Apache Software Foundation Incubator project, the server module implements JAX-RS.


I will provide a sample implementation for REST Web Service using JAX-RS in near future blog.
Until that please keep on reading :)


[1] http://docs.oracle.com/javaee/6/tutorial/doc/giepu.html
[2] http://en.wikipedia.org/wiki/Java_API_for_RESTful_Web_Services