I had two applications that communicate with each other through web-services. There I had a requirement to send multi-part file from one application to another. After searching I came out with the following solution and thought to share:

import org.apache.http.entity.mime.MultipartEntity
import org.apache.http.entity.mime.HttpMultipartMode
import org.apache.http.entity.mime.content.InputStreamBody
import org.apache.http.entity.mime.content.StringBody
import groovyx.net.http.*

void sendMultiPartFile(CommonsMultipartFile multipartImageFile, String cityName) {

 def http = new HTTPBuilder("http://www.anotherapp.com/controller/action")

 http.request(Method.POST) { req ->

 requestContentType: "multipart/form-data"

 MultipartEntity multiPartContent = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE)

 // Adding Multi-part file parameter "imageFile"

 multiPartContent.addPart("imageFile", new InputStreamBody(multipartImageFile.inputStream, multipartImageFile.contentType, multipartImageFile.originalFilename))

 // Adding another string parameter "city"

 multiPartContent.addPart("city", new StringBody(cityName))

 req.setEntity(multiPartContent)

 response.success = { resp ->

        if (resp.statusLine.statusCode == 200) {

                  // response handling

                   }
            }
      }
}

Hope it would help!!!
~~
Regards
Divya Setia
divya@intelligrape.com