Question

I am writing a Grails app, and I want the controller to hit some other API with a POST and then use the response to generate the page my user sees. I am not able to Google the right terms to find anything about posting to another page and receiving the response with Grails. Links to tutorials or answers like “Thats called…” would me much appreciated.

Answer 1

Seems like you are integrating with some sort of RESTful web service. There is REST client plugin, linked here.

Alternatively, its quite easy to do this without a plugin, linked here.

I highly recommend letting your controller just be a controller. Abstract your interface with this outside service into some class like OtherApiService or some sort of utility. Keep all the code that communicates with this outside service in one place; that way you can mock your integration component and make testing everywhere else easy. If you do this as a service, you have room to expand, say in the case you want to start storing some data from the API in your own app.

Anyway, cutting and posting from the linked documentation (the second link), the following shows how to send a GET to an API and how to set up handlers for success and failures, as well as dealing with request headers and query params — this should have everything you need.

@Grab(group='org.codehaus.groovy.modules.http-builder', module='http-builder', version='0.5.0-RC2' )
import groovyx.net.http.*
import static groovyx.net.http.ContentType.*
import static groovyx.net.http.Method.*

def http = new HTTPBuilder( 'http://ajax.googleapis.com' )

// perform a GET request, expecting JSON response data
http.request( GET, JSON ) {
  uri.path = '/ajax/services/search/web'
  uri.query = [ v:'1.0', q: 'Calvin and Hobbes' ]

  headers.'User-Agent' = 'Mozilla/5.0 Ubuntu/8.10 Firefox/3.0.4'

  // response handler for a success response code:
  response.success = { resp, json ->
    println resp.statusLine

    // parse the JSON response object:
    json.responseData.results.each {
      println "  ${it.titleNoFormatting} : ${it.visibleUrl}"
    }
  }

  // handler for any failure status code:
  response.failure = { resp ->
    println "Unexpected error: ${resp.statusLine.statusCode} : ${resp.statusLine.reasonPhrase}"
  }
}

You might also want to check out this, for some nifty tricks. Is has an example with a POST method.