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The following topics are covered under Message Translator EIP.

Introduction to Message Translator

Different Applications typically use different data types. Therefore, for two applications to successfully communicate, we should intermediately translate the messages that pass from one application to the data type compatible with the receiving application. A translator changes the context of a message from one interface to another, allowing message to adhere to message context rules of the back-end service.

The Message Translator EIP is responsible for message translating to ensure compatibility between applications supporting different data types. For more information, refer to http://www.eaipatterns.com/MessageTranslator.html

 

 

 

 

 

Figure 1: Message Translator EIP

Example Scenario for the EIP

The rest of this document explains, through an example scenario, how the Message Translator EIP can be simulated using WSO2 ESB. The example scenario is an inventory for stocks. It illustrates how the sender sends a request in one format, which is then transformed into another format compatible with the receiver. The format of the request is as follows.

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
   <soapenv:Header>    
   </soapenv:Header> 
   <soapenv:Body>
        <ser:Code>Foo</ser:Code>
   </soapenv:Body>
</soapenv:Envelope>

 The message format compatible with the receiver is as follow.

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
   <soapenv:Header/>
   <soapenv:Body>
      <ser:getQuote>
         <!--Optional:-->
         <ser:request>
            <!--Optional:-->
            <ser:symbol>Foo</ser:symbol>
         </ser:request>
      </ser:getQuote>
   </soapenv:Body>
</soapenv:Envelope>

All requests in the first format should be translated to the second through the WSO2 ESB.

Implementing the Example Scenario in WSO2 ESB

Getting Started

The diagram below depicts how to simulate the example scenario using the WSO2 ESB.

Figure 2: Example Scenario of the Message Translator EIP

Before digging into implementation details, let's take a look at the relationship between the example scenario and the  Message Translator  EIP by comparing their core components.

Figure 1: Message Translator EIPFigure 2: Message Translator Example Scenario

Incoming Message

Stock Quote Request

Translator

 

The translation is done through the Payload Factory Mediator

Environment Set up

1. Download and install the WSO2 ESB from http://wso2.com/products/enterprise-service-bus. For a list of prerequisites and step-by-step installation instructions, refer to Getting Started in the WSO2 ESB documentation.

2. Start an instance of Axis2 server. For instructions, refer to section ESB Samples Setup - Starting Sample Back-End Services in the WSO2 ESB Documentation.

ESB Configuration

3. Start the ESB server and log in to its management console UI (https://localhost:9443/carbon). In the management console, navigate to Main Menu, click Service Bus and then Source View. Next, copy and paste the following configuration, which helps you explore the example scenario, to the source view.

<definitions xmlns="http://ws.apache.org/ns/synapse">
   <sequence name="fault">
      <log level="full">
         <property name="MESSAGE" value="Executing default &#34;fault&#34; sequence"/>
         <property name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
         <property name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
      </log>
      <drop/>
   </sequence>
   <!-- Will trigger when a request is sent to the ESB --> 
   <sequence name="main">
      <in>
		 <!-- Will transform the incoming message to the format specified below --> 
		 <payloadFactory>
            <format>
               <m:getQuote xmlns:m="http://services.samples">
                  <m:request>
                     <m:symbol>$1</m:symbol>
                  </m:request>
               </m:getQuote>
            </format>
            <args>
               <arg xmlns:m0="http://services.samples" expression="//m0:Code"/>
            </args>
         </payloadFactory>
         <send>
            <endpoint>
               <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
            </endpoint>
         </send>
      </in>
      <out>      
      	<send/>
	  </out>
   </sequence>
</definitions>

Simulating the Sample Scenario

4. Send a request using a SOAP request client (ex :- SOAP UI) to WSO2 ESB in the following manner,

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
   <soapenv:Header>    
   </soapenv:Header> 
   <soapenv:Body>
        <ser:Code>Foo</ser:Code>
   </soapenv:Body>
</soapenv:Envelope>

After sending the request to the ESB through the client, the client should be able to notice that the request is successfully generated in the stock quote server.

How the Implementation Works

Let's investigate the elements of the ESB configuration in detail. The line numbers below refer to the ESB configuration in step 3 above.

  • main sequence [line 12 in ESB config] - The default sequence which triggers when the user invokes the ESB server.
  • in [line 13 in ESB config] - Once the message hits the main sequence, it will be diverted to in sequence.
  • out [line 33 in ESB config] - Will be triggered after execution of steps defined through the in sequence.
  • payload factory [line 15 in ESB config] - Will transform the message to the format denoted within the mediator.
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