Sample 380: Writing your own Custom Mediation in Java

Objective: Demonstrate the use of Class mediator to extend the mediation functionality.

<definitions xmlns="http://ws.apache.org/ns/synapse">

    <sequence name="fault">
        <makefault>
            <code value="tns:Receiver" xmlns:tns="http://www.w3.org/2003/05/soap-envelope"/>
            <reason value="Mediation failed."/>
        </makefault>
        <send/>
    </sequence>

    <sequence name="main" onError="fault">
        <in>
            <send>
                <endpoint name="stockquote">
                    <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
                </endpoint>
            </send>
        </in>
        <out>
            <class name="samples.mediators.DiscountQuoteMediator">
                <property name="discountFactor" value="10"/>
                <property name="bonusFor" value="5"/>
            </class>
            <send/>
        </out>
    </sequence>

</definitions>

Prerequisites:

Make sure the synapse-samples-1.0.jar is in your class path (by default this jar is placed in the lib directory when installing ESB).
Start ESB with the sample configuration 380 (i.e. wso2esb-samples -sn 380)
Start the sample Axis2 server and deploy the SimpleStockQuoteService.

In this configuration, ESB hands over the request message to the specified endpoint, which sends it to the Axis2 server running on port 9000. But the response message is passed through the class mediator before sending it back to the client. Two parameters named "discountFactor" and "bonusFor" are passed to the instance mediator implementation class (i.e. samples.mediators.DiscountQuoteMediator) before each invocation. Code of the mediator implementation class is shown below.

package samples.mediators;

import org.apache.synapse.MessageContext;
import org.apache.synapse.Mediator;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.soap.SOAPFactory;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import javax.xml.namespace.QName;

public class DiscountQuoteMediator implements Mediator {

    private static final Log log = LogFactory.getLog(DiscountQuoteMediator.class);

    private String discountFactor="10";

    private String bonusFor="10";

    private int bonusCount=0;

    public DiscountQuoteMediator(){}

    public boolean mediate(MessageContext mc) {

        String price= mc.getEnvelope().getBody().getFirstElement().getFirstElement().
                getFirstChildWithName(new QName("http://services.samples/xsd","last")).getText();

        //converting String properties into integers
        int discount=Integer.parseInt(discountFactor);
        int bonusNo=Integer.parseInt(bonusFor);
        double currentPrice=Double.parseDouble(price);

        //discounting factor is deducted from current price form every response
        Double lastPrice = new Double(currentPrice - currentPrice * discount / 100);

        //Special discount of 5% offers for the first responses as set in the bonusFor property
        if (bonusCount <= bonusNo) {
            lastPrice = new Double(lastPrice.doubleValue() - lastPrice.doubleValue() * 0.05);
            bonusCount++;
        }

        String discountedPrice = lastPrice.toString();

        mc.getEnvelope().getBody().getFirstElement().getFirstElement().getFirstChildWithName
                (new QName("http://services.samples/xsd","last")).setText(discountedPrice);

        System.out.println("Quote value discounted.");
        System.out.println("Original price: " + price);
        System.out.println("Discounted price: " + discountedPrice);

        return true;
    }

    public String getType() {
        return null;
    }

    public void setTraceState(int traceState) {
        traceState = 0;
    }

    public int getTraceState() {
        return 0;
    }

    public void setDiscountFactor(String discount) {
        discountFactor=discount;
    }

    public String getDiscountFactor() {
        return discountFactor;
    }

    public void setBonusFor(String bonus){
        bonusFor=bonus;
    }

    public String getBonusFor(){
        return bonusFor;
    }
}

All classes developed for class mediation should implement the Mediator interface, which contains the mediate(...) method. mediate(...) method of the above class is invoked for each response message mediated through the main sequence, with the message context of the current message as the parameter. All the details of the message including the SOAP headers, SOAP body and properties of the context hierarchy can be accessed from the message context. In this sample, the body of the message is retrieved and the discount percentage is subtracted from the quote price. If the quote request number is less than the number specified in the "bonusFor" property in the configuration, a special discount is given.

Now run the client using the following command.

ant stockquote -Dsymbol=IBM -Dmode=quote -Daddurl=http://localhost:8280

You will see the below output in the client console with the discounted quote value.

[java] Standard :: Stock price = $138.77458254967408

Now check the console running Synapse. You will see the original value and the discounted value for the requested quote as follows.

Quote value discounted.
Original price: 162.30945327447262
Discounted price: 138.77458254967408