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This example demonstrates how the ESB uses messaging to invoke the functionality provided by an application. A command message can be in any form, including a JMS serialized object or a text message in the form of an XML or SOAP request. In this example, the ESB will pass the message as a document to a sample Axis2 server and invoke the operation directly using the Callout mediator.

The following diagram below depicts how to simulate the example scenario this example can be simulated using the ESB.:

Figure 2: Example scenario of the Command Message EIP

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The configuration elements

Let's investigate the elements of the configuration in detailThe elements used in the above ESB configuration are explained below.

• <callout> - The callout mediator specifies a particular method to invoke in the back-end service. This invocation is blocking.  
• <source> - The source specifies the payload for the method invocation using xPath expressions. 
• <target> - The target specifies the location where the response should be concatenated.

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You need to set up the ESB, and the back-end service:

1. Download the Command-Message_1.0.0.zip file, which includes the ESB configuration described above. 

2. See Setting up the Environment for instructions on setting up the ESB and the back-end service.

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   When you set up the environment, note that you only need to start one instance of the back-end service (Stock Quote Service) to simulate this example.

Executing the sample

Let's send a request to the ESB using the Stock Quote Client application. Find out more about the Stock Quote Client from the ESB documentation.

1. Open a new terminal, and navigate to the <ESB_HOME>/samples/axis2Client/ directory. The Stock Quote client application is stored in this directory.

2. Execute the following command to send the request to the ESB.

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   ant stockquote -Dtrpurl=http://localhost:8280/services/command-message-proxy

Analyzing the output

The client receives the stock quote as the response. 
Stock Quote Client response: 

Standard :: Stock price = $85.09378162206208

Axis2 server response: 

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When you execute the command above, the ESB first receives the message and then routes it to the back-end service (StockQuoteService). The following output will be printed on the Axis2 server's console: 

samples.services.SimpleStockQuoteService :: Generating quote for : IBM

The generated stock quote will then be sent to the client application (Stock Quote Client). The following output will be printed on the client application's console:

Standard :: Stock price = $85.09378162206208