Document Message

This section explains, through an example scenario, how the Document Message EIP can be implemented using the WSO2 ESB. The following topics are covered:

Introduction to Document Message

The Document Message EIP is used to reliably transfer a data structure between applications. The Command Message EIP allows you to invoke only a specific client through the ESB, while the Document Message EIP sends the entire data unit to the receiver. For more information, see http://www.eaipatterns.com/DocumentMessage.html.

Figure 1: Document Message EIP

Example scenario

This example demonstrates how the ESB transmits an entire message from a client to a sample Axis2 server as a document message. Then the Axis2 server processes the message and identifies which operation to invoke.

The following diagram depicts this process.

Figure 2: Example scenario of the Document Message EIP

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

Document Message EIP (Figure 1)	Document Message Example Scenario (Figure 2)
Sender	Stock Quote Client
Document Message	Proxy Service
Receiver	Simple Stock Quote Service

The ESB configuration

Given below is the ESB configuration for simulating the example scenario explained above.

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="http://ws.apache.org/ns/synapse">
   <proxy name="DocumentMessageProxy" transports="https http" startOnLoad="true" trace="disable">
      <target>
         <inSequence>
            <send>
               <endpoint>
                  <address uri="http://localhost:9000/services/SimpleStockQuoteService" />
               </endpoint>
            </send>
         </inSequence>
         <outSequence>
            <send />
         </outSequence>
      </target>
   </proxy>
</definitions>

The configuration elements

The elements used in the above ESB configuration are explained below.

Proxy Service - The proxy service takes a request and forwards it to the back-end service, abstracting the routing logic from the client. In this example scenario, the proxy service just forwards the request to the back-end service, following the Document Message EIP.

Simulating the example scenario

Now, let's try out the example scenario explained above.

Setting up the environment

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

Download the Document-Message_1.0.0.zip file, which includes the ESB configuration described above.
See Setting up the Environment for instructions on setting up the ESB and the back-end service.

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.

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

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

ant stockquote -Dtrpurl=http://localhost:8280/services/DocumentMessageProxy

Analyzing the output

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 = $72.42070059233666