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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.

Before digging into implementation details, let's take a look at the co-relation of 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 Setup

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 Installation Guide 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 WSO2 ESB and copy the following configuration to the "Source View" in the management console (Main Menu -> Service Bus -> Source View), using which the example scenario can be explored.

 

<?xml version="1.0" encoding="UTF-8"?>
<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>

When the above request was sent to the ESB through the client. the client will be able to notice that the request was 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 are mapped with the ESB configuration illustrated in step 3 above.

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