What's covered: creating API prototypes using mediation policies for APIM 1.10.0
WSO2 API Manager comes with API prototyping capability OOTB. However if you are in need of advanced prototyping capabilities or feel restricted by the available implementation for the time being you could tap into the underlying mediation engine (WSO2 ESB) to meet your prototyping need.

1) Create a Mediation Policy With the Prototype Logic

The mediation policy should be such that it responds back to the client with the configured response rather than passing the message back to the backend. We can achieve this requirement using Respond [1] and Payload Factory mediators [2].

 <sequence xmlns="http://ws.apache.org/ns/synapse" name="prototypesequence">
   <header name="To" action="remove"></header>
   <header name="CustomHeader" scope="transport" value="test123"></header>
   <property name="RESPONSE" value="true"></property>
   <property name="NO_ENTITY_BODY" action="remove" scope="axis2"></property>
   <payloadFactory media-type="json">
      <format>               {"id":"101","name": "dumiduh","desc": "hard coded json"}            </format>
   </payloadFactory>
   <class name="org.wso2.carbon.apimgt.usage.publisher.APIMgtResponseHandler"/>
   <respond></respond>
</sequence>

The example above is using a hardcoded response body and headers, you could also populate the response with variables as required [3]. Find the example mediation policy here [4].

2) Attach Mediation Policy to API in Flow

Start creating an API with required HTTP methods etc, select Manage API from implementation and from Message Mediation Policies section upload the prototype mediation policy. Publish the API.

3) Invoke

Invoke the API as you would any other managed API [5].

[1] - https://docs.wso2.com/display/ESB490/Respond+Mediator
[2] - https://docs.wso2.com/display/ESB490/PayloadFactory+Mediator
[3] -https://docs.wso2.com/display/ESB490/PayloadFactory+Mediator#PayloadFactoryMediator-Example3:Addingarguments
[4] -  https://drive.google.com/file/d/0B9oVIeyHJKBXb0xkTGUwSmlJc0E/view?usp=sharing
[5] - https://docs.wso2.com/display/AM1100/Quick+Start+Guide