How to POST to REST api from Mule Flow?

I need some help with Mule 3 esb. I am reading a message from a JMS Queue and then I want to POST some parts of this message to an external REST api and handle the response. I have only used Mule to talk to databases before and never for web services. Can you help me figure out what I need to do to correctly POST to this api and handle the response. Should I use a java component instead of doing it in the flow?

Here is a sample XML message from the JMS queue

<longUrl>http://www.cnn.com</longUrl>

Here is my flow

<flow name="myFlow" doc:name="myFlow">

    <jms:inbound-endpoint queue="input" connector-ref="jmsConnector" doc:name="JMS">
        <jms:transaction action="ALWAYS_BEGIN"/>
    </jms:inbound-endpoint>        

    <logger message="#[payload]" level="INFO" doc:name="Logger"/>

    <choice doc:name="Choice">
        <when expression="payload.size() &gt; 0" evaluator="groovy">
            <processor-chain>
                <logger message="****** Create short url *******" level="INFO" doc:name="Logger"/>                                        
                <https:outbound-endpoint method="POST" exchange-pattern="request-response" address="https://www.googleapis.com/urlshortener/v1/url" contentType="application/json" doc:name="HTTP"/>
            </processor-chain>
        </when>
        <otherwise>
            <processor-chain>
                <message-properties-transformer doc:name="Message Properties">
                    <add-message-property key="Content-Type" value="text/plain"/>
                </message-properties-transformer>
                <expression-transformer doc:name="Expression">
                    <return-argument evaluator="string" expression="no parameter is given!"/>
                </expression-transformer>
            </processor-chain>
        </otherwise>
    </choice>      

</flow>

Solution

You need to transform the XML into JSON before POSTing to the Google API.

I did this in two steps:

extract the long URL with XPath and create a map out of it,
transform the map to JSON.

Here is the relevant configuration bit:

<processor-chain>
    <logger message="****** Create short url *******"
        level="INFO" doc:name="Logger" />
    <expression-transformer expression="['longUrl':xpath('/longUrl').stringValue]" />
    <json:object-to-json-transformer />
    <https:outbound-endpoint
        method="POST" exchange-pattern="request-response"
        address="https://www.googleapis.com/urlshortener/v1/url"
        contentType="application/json" doc:name="HTTP" />
</processor-chain>

With this in place, I get a correct JSON response:

{
 "kind": "urlshortener#url",
 "id": "http://goo.gl/2ViC",
 "longUrl": "http://www.cnn.com/"
}