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§The Play WS API

Sometimes we would like to call other HTTP services from within a Play application. Play supports this via its WS library, which provides a way to make asynchronous HTTP calls.

There are two important parts to using the WS API: making a request, and processing the response. We’ll discuss how to make both GET and POST HTTP requests first, and then show how to process the response from WS. Finally, we’ll discuss some common use cases.

§Making a Request

To use WS, first add ws to your build.sbt file:

libraryDependencies ++= Seq(
  ws
)

Now any controller or component that wants to use WS will have to declare a dependency on the WSClient:

import javax.inject.Inject
import scala.concurrent.Future

import play.api.mvc._
import play.api.libs.ws._

class Application @Inject() (ws: WSClient) extends Controller {

}

We’ve called the WSClient instance ws, all the following examples will assume this name.

To build an HTTP request, you start with ws.url() to specify the URL.

val request: WSRequest = ws.url(url)

This returns a WSRequest that you can use to specify various HTTP options, such as setting headers. You can chain calls together to construct complex requests.

val complexRequest: WSRequest =
  request.withHeaders("Accept" -> "application/json")
    .withRequestTimeout(10000)
    .withQueryString("search" -> "play")

You end by calling a method corresponding to the HTTP method you want to use. This ends the chain, and uses all the options defined on the built request in the WSRequest.

val futureResponse: Future[WSResponse] = complexRequest.get()

This returns a Future[WSResponse] where the Response contains the data returned from the server.

§Request with authentication

If you need to use HTTP authentication, you can specify it in the builder, using a username, password, and an AuthScheme. Valid case objects for the AuthScheme are BASIC, DIGEST, KERBEROS, NONE, NTLM, and SPNEGO.

ws.url(url).withAuth(user, password, WSAuthScheme.BASIC).get()

§Request with follow redirects

If an HTTP call results in a 302 or a 301 redirect, you can automatically follow the redirect without having to make another call.

ws.url(url).withFollowRedirects(true).get()

§Request with query parameters

Parameters can be specified as a series of key/value tuples.

ws.url(url).withQueryString("paramKey" -> "paramValue").get()

§Request with additional headers

Headers can be specified as a series of key/value tuples.

ws.url(url).withHeaders("headerKey" -> "headerValue").get()

If you are sending plain text in a particular format, you may want to define the content type explicitly.

ws.url(url).withHeaders("Content-Type" -> "application/xml").post(xmlString)

§Request with virtual host

A virtual host can be specified as a string.

ws.url(url).withVirtualHost("192.168.1.1").get()

§Request with timeout

If you wish to specify a request timeout, you can use withRequestTimeout to set a value in milliseconds. A value of -1 can be used to set an infinite timeout.

ws.url(url).withRequestTimeout(5000).get()

§Submitting form data

To post url-form-encoded data a Map[String, Seq[String]] needs to be passed into post.

ws.url(url).post(Map("key" -> Seq("value")))

§Submitting JSON data

The easiest way to post JSON data is to use the JSON library.

import play.api.libs.json._
val data = Json.obj(
  "key1" -> "value1",
  "key2" -> "value2"
)
val futureResponse: Future[WSResponse] = ws.url(url).post(data)

§Submitting XML data

The easiest way to post XML data is to use XML literals. XML literals are convenient, but not very fast. For efficiency, consider using an XML view template, or a JAXB library.

val data = <person>
  <name>Steve</name>
  <age>23</age>
</person>
val futureResponse: Future[WSResponse] = ws.url(url).post(data)

§Processing the Response

Working with the Response is easily done by mapping inside the Future.

The examples given below have some common dependencies that will be shown once here for brevity.

Whenever an operation is done on a Future, an implicit execution context must be available - this declares which thread pool the callback to the future should run in. The default Play execution context is often sufficient:

implicit val context = play.api.libs.concurrent.Execution.Implicits.defaultContext

The examples also use the folowing case class for serialization / deserialization:

case class Person(name: String, age: Int)

§Processing a response as JSON

You can process the response as a JSON object by calling response.json.

val futureResult: Future[String] = ws.url(url).get().map {
  response =>
    (response.json \ "person" \ "name").as[String]
}

The JSON library has a useful feature that will map an implicit Reads[T] directly to a class:

import play.api.libs.json._

implicit val personReads = Json.reads[Person]

val futureResult: Future[JsResult[Person]] = ws.url(url).get().map {
  response => (response.json \ "person").validate[Person]
}

§Processing a response as XML

You can process the response as an XML literal by calling response.xml.

val futureResult: Future[scala.xml.NodeSeq] = ws.url(url).get().map {
  response =>
    response.xml \ "message"
}

§Processing large responses

Calling get() or post() will cause the body of the request to be loaded into memory before the response is made available. When you are downloading with large, multi-gigabyte files, this may result in unwelcome garbage collection or even out of memory errors.

WS lets you use the response incrementally by using an iteratee. The stream() and getStream() methods on WSRequest return Future[(WSResponseHeaders, Enumerator[Array[Byte]])]. The enumerator contains the response body.

Here is a trivial example that uses an iteratee to count the number of bytes returned by the response:

import play.api.libs.iteratee._

// Make the request
val futureResponse: Future[(WSResponseHeaders, Enumerator[Array[Byte]])] =
  ws.url(url).getStream()

val bytesReturned: Future[Long] = futureResponse.flatMap {
  case (headers, body) =>
    // Count the number of bytes returned
    body |>>> Iteratee.fold(0l) { (total, bytes) =>
      total + bytes.length
    }
}

Of course, usually you won’t want to consume large bodies like this, the more common use case is to stream the body out to another location. For example, to stream the body to a file:

import play.api.libs.iteratee._

// Make the request
val futureResponse: Future[(WSResponseHeaders, Enumerator[Array[Byte]])] =
  ws.url(url).getStream()

val downloadedFile: Future[File] = futureResponse.flatMap {
  case (headers, body) =>
    val outputStream = new FileOutputStream(file)

    // The iteratee that writes to the output stream
    val iteratee = Iteratee.foreach[Array[Byte]] { bytes =>
      outputStream.write(bytes)
    }

    // Feed the body into the iteratee
    (body |>>> iteratee).andThen {
      case result =>
        // Close the output stream whether there was an error or not
        outputStream.close()
        // Get the result or rethrow the error
        result.get
    }.map(_ => file)
}

Another common destination for response bodies is to stream them through to a response that this server is currently serving:

def downloadFile = Action.async {

  // Make the request
  ws.url(url).getStream().map {
    case (response, body) =>

      // Check that the response was successful
      if (response.status == 200) {

        // Get the content type
        val contentType = response.headers.get("Content-Type").flatMap(_.headOption)
          .getOrElse("application/octet-stream")

        // If there's a content length, send that, otherwise return the body chunked
        response.headers.get("Content-Length") match {
          case Some(Seq(length)) =>
            Ok.feed(body).as(contentType).withHeaders("Content-Length" -> length)
          case _ =>
            Ok.chunked(body).as(contentType)
        }
      } else {
        BadGateway
      }
  }
}

POST and PUT calls require manually calling the withMethod method, eg:

val futureResponse: Future[(WSResponseHeaders, Enumerator[Array[Byte]])] =
  ws.url(url).withMethod("PUT").withBody("some body").stream()

§Common Patterns and Use Cases

§Chaining WS calls

Using for comprehensions is a good way to chain WS calls in a trusted environment. You should use for comprehensions together with Future.recover to handle possible failure.

val futureResponse: Future[WSResponse] = for {
  responseOne <- ws.url(urlOne).get()
  responseTwo <- ws.url(responseOne.body).get()
  responseThree <- ws.url(responseTwo.body).get()
} yield responseThree

futureResponse.recover {
  case e: Exception =>
    val exceptionData = Map("error" -> Seq(e.getMessage))
    ws.url(exceptionUrl).post(exceptionData)
}

§Using in a controller

When making a request from a controller, you can map the response to a Future[Result]. This can be used in combination with Play’s Action.async action builder, as described in Handling Asynchronous Results.

def wsAction = Action.async {
  ws.url(url).get().map { response =>
    Ok(response.body)
  }
}
status(wsAction(FakeRequest())) must_== OK

§Using WSClient

WSClient is a wrapper around the underlying AsyncHttpClient. It is useful for defining multiple clients with different profiles, or using a mock.

You can define a WS client directly from code without having it injected by WS, and then use it implicitly with WS.clientUrl():

import play.api.libs.ws.ning._

implicit val sslClient = NingWSClient()
// close with sslClient.close() when finished with client
val response = WS.clientUrl(url).get()

NOTE: if you instantiate a NingWSClient object, it does not use the WS module lifecycle, and so will not be automatically closed in Application.onStop. Instead, the client must be manually shutdown using client.close() when processing has completed. This will release the underlying ThreadPoolExecutor used by AsyncHttpClient. Failure to close the client may result in out of memory exceptions (especially if you are reloading an application frequently in development mode).

or directly:

val response = sslClient.url(url).get()

Or use a magnet pattern to match up certain clients automatically:

object PairMagnet {
  implicit def fromPair(pair: (WSClient, java.net.URL)) =
    new WSRequestMagnet {
      def apply(): WSRequest = {
        val (client, netUrl) = pair
        client.url(netUrl.toString)
      }
    }
}

import scala.language.implicitConversions
import PairMagnet._

val exampleURL = new java.net.URL(url)
val response = WS.url(ws -> exampleURL).get()

By default, configuration happens in application.conf, but you can also set up the builder directly from configuration:

import com.typesafe.config.ConfigFactory
import play.api._
import play.api.libs.ws._
import play.api.libs.ws.ning._

val configuration = Configuration.reference ++ Configuration(ConfigFactory.parseString(
  """
    |ws.followRedirects = true
  """.stripMargin))

// If running in Play, environment should be injected
val environment = Environment(new File("."), this.getClass.getClassLoader, Mode.Prod)

val parser = new WSConfigParser(configuration, environment)
val config = new NingWSClientConfig(wsClientConfig = parser.parse())
val builder = new NingAsyncHttpClientConfigBuilder(config)

You can also get access to the underlying async client.

import com.ning.http.client.AsyncHttpClient

val client: AsyncHttpClient = ws.underlying

This is important in a couple of cases. WS has a couple of limitations that require access to the client:

§Configuring WS

Use the following properties in application.conf to configure the WS client:

§Configuring WS with SSL

To configure WS for use with HTTP over SSL/TLS (HTTPS), please see Configuring WS SSL.

§Configuring Timeouts

There are 3 different timeouts in WS. Reaching a timeout causes the WS request to interrupt.

The request timeout can be overridden for a specific connection with withRequestTimeout() (see “Making a Request” section).

§Configuring AsyncHttpClientConfig

The following advanced settings can be configured on the underlying AsyncHttpClientConfig.
Please refer to the AsyncHttpClientConfig Documentation for more information.

Next: Connecting to OpenID services


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