Mule ESB HTTP POST Request with URL-Form-Encoded Body - http

Question

I'm new in Mule ESB and trying to send a post request to a REST Service. The body of the request is in String form and the request should be x-www-form-urlencoded. I set the payload to my parameters and send the request to the REST Service but I get an exception:
Failed to invoke REST service "http://username:password#192.168.10.252/api/rest/session/login.json". Message payload is of type: String
My Rest URL is: (#[restURL]) ${dms.host}/api/rest/session/login.json
My parameter is (set as payload #[restBody]): username=user&password=pass
<sub-flow name="RESTrequestToDMS" doc:name="RESTrequestToDMS" processingStrategy="synchronous">
<set-variable variableName="originalMessage" value="#[payload]" doc:name="Backup original message"/>
<logger message="#[restBody]" level="INFO" doc:name="Logger"/>
<choice doc:name="Choice">
<when expression="restHTTPmethod == 'POST'">
<processor-chain>
<set-payload value="#[restBody]" doc:name="Set Payload"/>
<http:rest-service-component httpMethod="POST" serviceUrl="http://${dms.user}:${dms.pass}##[restURL]"></http:rest-service-component>
</processor-chain>
</when>
<when expression="restHTTPmethod == 'GET'">
<processor-chain>
<http:rest-service-component httpMethod="GET" serviceUrl="http://${dms.user}:${dms.pass}##[restURL]?#[restBody]"></http:rest-service-component>
</processor-chain>
</when>
<otherwise>
<processor-chain>
<logger message="Unknown http method type is provided! " level="ERROR" doc:name="Logger"/>
</processor-chain>
</otherwise>
</choice>
<json:json-to-object-transformer returnClass="java.util.Map" doc:name="JSON to Object"/>
<echo-component doc:name="Echo"/>
<set-variable variableName="RESTResponse" value="#[payload]" doc:name="set RESTResponse"/>
<set-payload value="#[flowVars['originalMessage']]" doc:name="Restore Original Message"/>
</sub-flow>
Can somebody help me figure this out please?
Thanks a lot in advance.
Note: Updated according to David's reply.
-------------------UPDATE--------------------
So now, for testing purposes, I have modified the flow like this:
<set-payload value="#[restBody]" doc:name="Set Payload"/>
<custom-transformer class="de.mfg.osii.http.StringToURIParametersMapTransformer" doc:name="String To URI Parameters"/>
<http:rest-service-component httpMethod="POST" serviceUrl="http://${dms.user}:${dms.pass}##[restURL]">
<http:requiredParameter key="username" value="#[payload.get('username')]" />
<http:requiredParameter key="password" value="#[payload.get('password')]" />
</http:rest-service-component>
So now the payload is: {username=user, password=pass}
But now when I try to run this, I get the following error:
1. Failed to invoke REST service "http://user:pass#192.168.10.252/api/rest/session/login.json". Message payload is of type: LinkedHashMap (org.mule.transport.http.components.RestServiceException)
Update: The above problem, the exception, has just been solved by adding a message-property "Content-Type" with the value "application/x-www-form-urlencoded".
Still the last part, below, remains a mystery for me :)
The other thing is, as I stated in the comment to David's answer, can I add the required parameters for the rest component in an adaptive way? To be more clearer, I do not want to create different flows for every different request. I have the parameter map in the payload, so I want to iterate over them and put them in the required parameters. Is something like this possible?
Thanks a lot in advance!
-------------------UPDATE--------------------
So, I've modified my flow and used David's suggestions. However, now, I'm getting an HTTP 405 error (Method not allowed). But I'm sure I'm posting to the correct address with correct content-type. What is the reason for this? Does anybody have an idea?
My payload coming into this flow is a string (url encoded parameters) such as ->
sessionId=9eub9gm7k7oc1ub81dhef6t46q&xml=%3CObjectList%3E%3CFolderObject%3E%3CAddToFolder%20RefType%3D%22Path%22%20ClassName%3D%22FolderObject%22%3E%3C!%5BCDATA%5B%2FfolderPath%5D%5D%3E%3C%2FAddToFolder%3E%3CName%3E%3C!%5BCDATA%5Baaa%5D%5D%3E%3C%2FName%3E%3CDescription%3E%3C!%5BCDATA%5BRequests%20from%20user%20aaa%20are%20stored%20in%20this%20folder%5D%5D%3E%3C%2FDescription%3E%3CNoErrorIfExist%2F%3E%3C%2FFolderObject%3E%3C%2FObjectList%3E
<flow name="RESTrequestToDMS" doc:name="RESTrequestToDMS" processingStrategy="synchronous">
<set-variable variableName="originalMessage" value="#[payload]" doc:name="Backup original message"/>
<choice doc:name="Choice">
<when expression="restHTTPmethod == 'POST'">
<processor-chain>
<set-payload value="#[restBody]" doc:name="Set Payload"/>
<logger message="The payload before http post is: #[message.payload]" level="INFO" doc:name="Logger"/>
<http:outbound-endpoint exchange-pattern="request-response" doc:name="HTTP" address="http://#[restURL]" user="${dms.user}" password="${dms.pass}" contentType="application/x-www-form-urlencoded">
</http:outbound-endpoint>
</processor-chain>
</when>
<when expression="restHTTPmethod == 'GET'">
<processor-chain>
<http:outbound-endpoint method="GET" exchange-pattern="request-response" doc:name="HTTP" address="http://#[restURL]?#[restBody]" user="${dms.user}" password="${dms.pass}" contentType="application/x-www-form-urlencoded">
</http:outbound-endpoint>
</processor-chain>
</when>
<otherwise>
<processor-chain>
<logger message="Unknown http method type is provided! " level="ERROR" doc:name="Logger"/>
</processor-chain>
</otherwise>
</choice>
<echo-component doc:name="Echo"/>
<choice doc:name="Choice">
<when expression="payload != null && payload != empty && payload != ''">
<processor-chain>
<json:json-to-object-transformer doc:name="JSON to Object" returnClass="java.util.Map"/>
<set-variable variableName="RESTResponse" value="#[payload]" doc:name="set RESTResponse"/>
</processor-chain>
</when>
<otherwise>
<processor-chain>
<logger message="The payload is null or empty! HTTP response code is: #[message.inboundProperties['http.status']]" level="INFO" doc:name="Logger"/>
<set-variable variableName="RESTResponse" value="#[message.inboundProperties['http.status']]" doc:name="Set HTTP Status Code"/>
</processor-chain>
</otherwise>
</choice>
<set-payload value="#[flowVars['originalMessage']]" doc:name="Restore Original Message"/>
</flow>

Answer 1

Here is how you pass parameters to be URL encoded with the rest-service-component:
<http:rest-service-component httpMethod="POST"
serviceUrl="http://${dms.user}:${dms.pass}##[restURL]">
<http:requiredParameter key="username" value="user" />
<http:requiredParameter key="password" value="pass" />
</http:rest-service-component>