Groovy Script to test Rest Post Method with Json file and xml file with headers

i want to test the rest services using soap Ui  with groovy scripting.

i have the code for get method , like below sample 

import com.eviware.soapui.model.iface.Submit

def uri = "http://jsonplaceholder.typicode.com/posts/1"

WsdlProject project = new WsdlProject()
RestServiceBuilder serviceBuilder = new RestServiceBuilder()
serviceBuilder.createRestService(project, uri)

println "service name: "+project.getInterfaceList()[0].name

println "Resource: "+project.getInterfaceList()[0].getOperationList()[0]
RestRequest request = project.getInterfaceList()[0].getOperationList()[0].getRequestList()[0]
Submit submit = (Submit) request.submit( new WsdlSubmitContext(), false );

Response response = submit.getResponse();

String responseContent = response.getContentAsString();

println( responseContent );

but i dont know how to start with Post Method with Json or xml attachement....