Sample 16: Introduction to Dynamic and Static Registry Keys

Introduction

This Sample demonstrates the use of dynamic keys with mediators. Here the XSLT Mediator is used to demonstrate the difference between the static and dynamic usage of keys.

Prerequisites

For a list of prerequisites, see Prerequisites to Start the ESB Samples.

Building the sample

The XML configuration for this sample is as follows: 

<definitions xmlns="http://ws.apache.org/ns/synapse">
    <!-- the SimpleURLRegistry allows access to a URL based registry (e.g. file:/// or http://) -->
    <registry provider="org.wso2.carbon.mediation.registry.ESBRegistry">
        <!-- the root property of the simple URL registry helps resolve a resource URL as root + key -->
        <parameter name="root">file:repository/samples/resources/</parameter>
        <!-- all resources loaded from the URL registry would be cached for this number of milli seconds -->
        <parameter name="cachableDuration">15000</parameter>
    </registry>
    <sequence name="main">
        <in>
            <!-- define the request processing XSLT resource as a property value -->
            <property name="symbol" value="transform/transform.xslt"/>
            <!-- {} denotes that this key is a dynamic one and it is not a static key -->
            <!-- use Xpath expression "get-property()" to evaluate real key from property -->
            <xslt key="{get-property('symbol')}"/>
        </in>
        <out>
            <!-- transform the standard response back into the custom format the client expects -->
            <!-- the key is looked up in the remote registry using a static key -->
            <xslt key="transform/transform_back.xslt"/>
        </out>
        <send/>
    </sequence>
</definitions>

This configuration file  synapse_sample_16.xml is available in the <ESB_HOME>/repository/samples directory.

To build the sample

1. Start the ESB with the sample 16 configuration. For instructions on starting a sample ESB configuration, see Starting the ESB with a sample configuration.
   
   The operation log keeps running until the server starts, which usually takes several seconds. Wait until the server has fully booted up and displays a message similar to "WSO2 Carbon started in n seconds."

2. Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.

3. Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.

   Now you have a running ESB instance and a back-end service deployed. In the next section, we will send a message to the back-end service through the ESB using a sample client.

Executing the sample

The sample client used here is the Stock Quote Client, which can operate in several modes. For further details on this sample client and its operation modes, see Stock Quote Client.

According to the configuration file synapse_sample_16.xml, the first registry resource transform/transform.xslt is set as a property value. 

 Inside the XSLT mediator, the local property value is looked up using the Xpath expression get-property(). Similarly, any XPath expression can be enclosed within curly braces to denote that it is a dynamic key. Then the mediator evaluates the real value for that expression.

The second XSLT resource transform/transform_back.xslt is simply used as a static key. It is not included within curly braces since the mediator directly uses the static value as the key.

To execute the sample client

• Run the following command from the <ESB_HOME>/samples/axis2Client directory.

  ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService -Dtrpurl=http://localhost:8280/ -Dmode=customquote

Analyzing the output

When you analyze the debug log output on the ESB console, you will see an output similar to that of Sample 8: Introduction to Static and Dynamic Registry Resources and Using XSLT Transformations.