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5. Calling REST APIs with Play WS

§Calling REST APIs with Play WS

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 the WS library. Finally, we’ll discuss some common use cases.

Note: In Play 2.6, Play WS has been split into two, with an underlying standalone client that does not depend on Play, and a wrapper on top that uses Play specific classes. In addition, shaded versions of AsyncHttpClient and Netty are now used in Play WS to minimize library conflicts, primarily so that Play’s HTTP engine can use a different version of Netty. Please see the 2.6 migration guide for more information.

§Adding WS to project

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

libraryDependencies ++= Seq(
  ws
)

§Enabling HTTP Caching in Play WS

Play WS supports HTTP caching, but requires a JSR-107 cache implementation to enable this feature. You can add ehcache:

libraryDependencies += ehcache

Or you can use another JSR-107 compatible cache such as Caffeine.

Once you have the library dependencies, then enable the HTTP cache as shown on WS Cache Configuration page.

Using an HTTP cache means savings on repeated requests to backend REST services, and is especially useful when combined with resiliency features such as stale-on-error and stale-while-revalidate.

§Making a Request

Now any controller or component that wants to use WS will have to add the following imports and then declare a dependency on the WSClient type to use dependency injection:

import javax.inject.Inject;

import play.mvc.*;
import play.libs.ws.*;
import java.util.concurrent.CompletionStage;

public class MyClient implements WSBodyReadables, WSBodyWritables {
    private final WSClient ws;

    @Inject
    public MyClient(WSClient ws) {
        this.ws = ws;
    }
    // ...
}

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

WSRequest request = ws.url("http://example.com");

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.

WSRequest complexRequest = request.addHeader("headerKey", "headerValue")
                                        .setRequestTimeout(Duration.of(1000, ChronoUnit.MILLIS))
                                        .addQueryParameter("paramKey", "paramValue");

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.

CompletionStage<? extends WSResponse> responsePromise = complexRequest.get();

This returns a CompletionStage<WSResponse> where the WSResponse contains the data returned from the server.

Java 1.8 uses CompletionStage to manage asynchronous code, and Java WS API relies heavily on composing CompletionStage together with different methods. If you have been using an earlier version of Play that used F.Promise, then the CompletionStage section of the migration guide will be very helpful.

If you are doing any blocking work, including any kind of DNS work such as calling java.util.URL.equals(), then you should use a custom execution context as described in ThreadPools, preferably through a CustomExecutionContext. You should size the pool to leave a safety margin large enough to account for failures.

If you are calling out to an unreliable network, consider using Futures.timeout and a circuit breaker like Failsafe.

§Request with authentication

If you need to use HTTP authentication, you can specify it in the builder, using a username, password, and an WSAuthScheme. Options for the WSAuthScheme are BASIC, DIGEST, KERBEROS, NTLM, and SPNEGO.

ws.url(url).setAuth("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).setFollowRedirects(true).get();

§Request with query parameters

You can specify query parameters for a request.

ws.url(url).addQueryParameter("paramKey", "paramValue");

§Request with additional headers

ws.url(url).addHeader("headerKey", "headerValue").get();

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

ws.url(url).addHeader("Content-Type", "application/json").post(jsonString);
// OR
ws.url(url).setContentType("application/json").post(jsonString);

§Request with cookie

You can specify cookies for a request, using WSCookieBuilder:

ws.url(url).addCookies(new WSCookieBuilder().setName("headerKey").setValue("headerValue").build()).get();

§Request with timeout

If you wish to specify a request timeout, you can use setRequestTimeout to set a value in milliseconds. A value of Duration.ofMillis(Long.MAX_VALUE) can be used to set an infinite timeout.

ws.url(url).setRequestTimeout(Duration.of(1000, ChronoUnit.MILLIS)).get();

§Submitting form data

To post url-form-encoded data you can set the proper header and formatted data with a content type of “application/x-www-form-urlencoded”.

ws.url(url).setContentType("application/x-www-form-urlencoded")
           .post("key1=value1&key2=value2");

§Submitting multipart/form data

The easiest way to post multipart/form data is to use a Source<Http.MultipartFormData.Part<Source<ByteString>, ?>, ?>:

import play.libs.ws.ahc.AhcCurlRequestLogger;
import play.mvc.Http.MultipartFormData.*;

ws.url(url).post(Source.single(new DataPart("hello", "world")));

To upload a File as part of multipart form data, you need to pass a Http.MultipartFormData.FilePart<Source<ByteString>, ?> to the Source:

Source<ByteString, ?> file = FileIO.fromPath(Paths.get("hello.txt"));
FilePart<Source<ByteString, ?>> fp = new FilePart<>("hello", "hello.txt", "text/plain", file);
DataPart dp = new DataPart("key", "value");

ws.url(url).post(Source.from(Arrays.asList(fp, dp)));

§Submitting JSON data

The easiest way to post JSON data is to use Play’s JSON support, using play.libs.Json:

import com.fasterxml.jackson.databind.JsonNode;
import play.libs.Json;

JsonNode json = Json.newObject()
                    .put("key1", "value1")
                    .put("key2", "value2");

ws.url(url).post(json);

You can also pass in a custom ObjectMapper:

ObjectMapper objectMapper = play.libs.Json.newDefaultMapper();
ws.url(url).post(body(json, objectMapper));

§Submitting XML data

The easiest way to post XML data is to use Play’s XML support, using play.libs.XML:

Document xml = play.libs.XML.fromString("<document></document>");
ws.url(url).post(xml);

§Submitting Streaming data

It’s also possible to stream data in the request body using Akka Streams.

Here is an example showing how you could stream a large image to a different endpoint for further processing:

CompletionStage<WSResponse> wsResponse = ws.url(url).setBody(body(largeImage)).execute("PUT");

The largeImage in the code snippet above is a Source<ByteString, ?>.

§Request Filters

You can do additional processing on a WSRequest by adding a request filter. A request filter is added by extending the play.libs.ws.WSRequestFilter interface, and then adding it to the request with request.setRequestFilter(filter).

public CompletionStage<Result> index() {
    WSRequestFilter filter = executor -> request -> {
        logger.debug("url = " + request.getUrl());
        return executor.apply(request);
    };

    return ws.url(feedUrl)
            .setRequestFilter(filter)
            .get()
            .thenApply((WSResponse r) -> {
                String title = r.getBody(json()).findPath("title").asText();
                return ok("Feed title: " + title);
            });
}

A sample request filter that logs the request in cURL format to SLF4J has been added in play.libs.ws.ahc.AhcCurlRequestLogger.

ws.url("https://www.playframework.com")
  .setRequestFilter(new AhcCurlRequestLogger())
  .addHeader("Header-Name", "Header value")
  .get();

will output:

curl \
  --verbose \
  --request GET \
  --header 'Header-Key: Header value' \
  'https://www.playframework.com'

§Processing the Response

Working with the WSResponse is done by applying transformations such as thenApply and thenCompose to the CompletionStage.

§Processing a response as JSON

You can process the response as a JsonNode by calling r.getBody(json()), using the default method from play.libs.ws.WSBodyReadables.json().

// implements WSBodyReadables or use WSBodyReadables.instance.json()
CompletionStage<JsonNode> jsonPromise = ws.url(url).get()
        .thenApply(r -> r.getBody(json()));

§Processing a response as XML

Similarly, you can process the response as XML by calling r.getBody(xml()), using the default method from play.libs.ws.WSBodyReadables.xml().

// implements WSBodyReadables or use WSBodyReadables.instance.xml()
CompletionStage<Document> documentPromise = ws.url(url).get()
        .thenApply(r -> r.getBody(xml()));

§Processing large responses

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

You can consume the response’s body incrementally by using an Akka Streams Sink. The stream() method on WSRequest returns a CompletionStage<WSResponse>, where the WSResponse contains a getBodyAsStream() method that provides a Source<ByteString, ?>.

Note: In 2.5.x, a StreamedResponse was returned in response to a request.stream() call. In 2.6.x, a standard WSResponse is returned, and the getBodyAsSource() method should be used to return the Source.

Any controller or component that wants to leverage the WS streaming functionality will have to add the following imports and dependencies:

import javax.inject.Inject;

import akka.stream.Materializer;
import akka.stream.javadsl.*;
import akka.util.ByteString;

import play.mvc.*;
import play.libs.ws.*;

import scala.compat.java8.FutureConverters;

public class MyController extends Controller {

    @Inject WSClient ws;
    @Inject Materializer materializer;

    // ...
}

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

// Make the request
CompletionStage<WSResponse> futureResponse =
    ws.url(url).setMethod("GET").stream();

CompletionStage<Long> bytesReturned = futureResponse.thenCompose(res -> {
    Source<ByteString, ?> responseBody = res.getBodyAsSource();

    // Count the number of bytes returned
    Sink<ByteString, CompletionStage<Long>> bytesSum =
        Sink.fold(0L, (total, bytes) -> total + bytes.length());

    return responseBody.runWith(bytesSum, materializer);
});

Alternatively, you could also stream the body out to another location. For example, a file:

File file = File.createTempFile("stream-to-file-", ".txt");
OutputStream outputStream = java.nio.file.Files.newOutputStream(file.toPath());

// Make the request
CompletionStage<WSResponse> futureResponse =
    ws.url(url).setMethod("GET").stream();

CompletionStage<File> downloadedFile = futureResponse.thenCompose(res -> {
    Source<ByteString, ?> responseBody = res.getBodyAsSource();

    // The sink that writes to the output stream
    Sink<ByteString, CompletionStage<akka.Done>> outputWriter =
        Sink.<ByteString>foreach(bytes -> outputStream.write(bytes.toArray()));

    // materialize and run the stream
    CompletionStage<File> result = responseBody.runWith(outputWriter, materializer)
        .whenComplete((value, error) -> {
            // Close the output stream whether there was an error or not
            try { outputStream.close(); }
            catch(IOException e) {}
        })
        .thenApply(v -> file);
    return result;
});

Another common destination for response bodies is to stream them back from a controller’s Action:

// Make the request
CompletionStage<WSResponse> futureResponse = ws.url(url).setMethod("GET").stream();

CompletionStage<Result> result = futureResponse.thenApply(response -> {
    Source<ByteString, ?> body = response.getBodyAsSource();
    // Check that the response was successful
    if (response.getStatus() == 200) {
        // Get the content type
        String contentType =
                Optional.ofNullable(response.getHeaders().get("Content-Type"))
                        .map(contentTypes -> contentTypes.get(0))
                        .orElse("application/octet-stream");

        // If there's a content length, send that, otherwise return the body chunked
        Optional<String> contentLength = Optional.ofNullable(response.getHeaders()
                .get("Content-Length"))
                .map(contentLengths -> contentLengths.get(0));
        if (contentLength.isPresent()) {
            return ok().sendEntity(new HttpEntity.Streamed(
                    body,
                    Optional.of(Long.parseLong(contentLength.get())),
                    Optional.of(contentType)
            ));
        } else {
            return ok().chunked(body).as(contentType);
        }
    } else {
        return new Result(Status.BAD_GATEWAY);
    }
});

As you may have noticed, before calling stream() we need to set the HTTP method to use by calling setMethod(String) on the request. Here follows another example that uses PUT instead of GET:

CompletionStage<WSResponse> futureResponse  =
    ws.url(url).setMethod("PUT").setBody(body("some body")).stream();

Of course, you can use any other valid HTTP verb.

§Common Patterns and Use Cases

§Chaining WS calls

You can chain WS calls by using thenCompose.

final CompletionStage<WSResponse> responseThreePromise = ws.url(urlOne).get()
        .thenCompose(responseOne -> ws.url(responseOne.getBody()).get())
        .thenCompose(responseTwo -> ws.url(responseTwo.getBody()).get());

§Exception recovery

If you want to recover from an exception in the call, you can use handle or exceptionally to substitute a response.

CompletionStage<WSResponse> responsePromise = ws.url("http://example.com").get();
responsePromise.handle((result, error) -> {
    if (error != null) {
        return ws.url("http://backup.example.com").get();
    } else {
        return CompletableFuture.completedFuture(result);
    }
});

§Using in a controller

You can map a CompletionStage<WSResponse> to a CompletionStage<Result> that can be handled directly by the Play server, using the asynchronous action pattern defined in Handling Asynchronous Results.

public CompletionStage<Result> index() {
    return ws.url(feedUrl).get().thenApply(response ->
        ok("Feed title: " + response.asJson().findPath("title").asText())
    );
}

§Using WSClient with Futures Timeout

If a chain of WS calls does not complete in time, it may be useful to wrap the result in a timeout block, which will return a failed Future if the chain does not complete in time – this is more generic than using withRequestTimeout, which only applies to a single request.
The best way to do this is with Play’s non-blocking timeout feature, using Futures.timeout and CustomExecutionContext to ensure some kind of resolution:

public CompletionStage<Result> index() {
    CompletionStage<Result> f = futures.timeout(ws.url("http://playframework.com").get().thenApplyAsync(result -> {
        try {
            Thread.sleep(10000L);
            return Results.ok();
        } catch (InterruptedException e) {
            return Results.status(SERVICE_UNAVAILABLE);
        }
    }, customExecutionContext), 1L, TimeUnit.SECONDS);

    return f.handleAsync((result, e) -> {
        if (e != null) {
            if (e instanceof CompletionException) {
                Throwable completionException = e.getCause();
                if (completionException instanceof TimeoutException) {
                    return Results.status(SERVICE_UNAVAILABLE, "Service has timed out");
                } else {
                    return internalServerError(e.getMessage());
                }
            } else {
                logger.error("Unknown exception " + e.getMessage(), e);
                return internalServerError(e.getMessage());
            }
        } else {
            return result;
        }
    });
}

§Directly creating WSClient

We recommend that you get your WSClient instances using dependency injection as described above. WSClient instances created through dependency injection are simpler to use because they are automatically created when the application starts and cleaned up when the application stops.

However, if you choose, you can instantiate a WSClient directly from code and use this for making requests or for configuring underlying AsyncHttpClient options.

Note: If you create a WSClient manually then you must call client.close() to clean it up when you’ve finished with it. Each client creates its own thread pool. If you fail to close the client or if you create too many clients then you will run out of threads or file handles -— you’ll get errors like “Unable to create new native thread” or “too many open files” as the underlying resources are consumed.

Here is an example of how to create a WSClient instance by yourself:

import akka.stream.Materializer;
import akka.stream.javadsl.*;
import akka.util.ByteString;
import play.mvc.Results;

// Set up the client config (you can also use a parser here):
// play.api.Configuration configuration = ... // injection
// play.Environment environment = ... // injection

WSClient customWSClient = play.libs.ws.ahc.AhcWSClient.create(
        play.libs.ws.ahc.AhcWSClientConfigFactory.forConfig(
                configuration.underlying(),
                environment.classLoader()),
                null, // no HTTP caching
                materializer);

You can also use play.test.WSTestClient.newClient to create an instance of WSClient in a functional test. See JavaTestingWebServiceClients for more details.

Or, you can run the WSClient completely standalone without involving a running Play application or configuration at all:

import akka.actor.ActorSystem;
import akka.stream.ActorMaterializer;
import akka.stream.ActorMaterializerSettings;
import org.junit.Test;
import play.shaded.ahc.org.asynchttpclient.*;
import play.libs.ws.*;
import play.libs.ws.ahc.*;

// Set up Akka
String name = "wsclient";
ActorSystem system = ActorSystem.create(name);
ActorMaterializerSettings settings = ActorMaterializerSettings.create(system);
ActorMaterializer materializer = ActorMaterializer.create(settings, system, name);

// Set up AsyncHttpClient directly from config
AsyncHttpClientConfig asyncHttpClientConfig = new DefaultAsyncHttpClientConfig.Builder()
        .setMaxRequestRetry(0)
        .setShutdownQuietPeriod(0)
        .setShutdownTimeout(0).build();
AsyncHttpClient asyncHttpClient = new DefaultAsyncHttpClient(asyncHttpClientConfig);

// Set up WSClient instance directly from asynchttpclient.
WSClient client = new AhcWSClient(
    asyncHttpClient,
    materializer
);

// Call out to a remote system and then and close the client and akka.
client.url("http://www.google.com").get().whenComplete((r, e) -> {
    Optional.ofNullable(r).ifPresent(response -> {
        String statusText = response.getStatusText();
        System.out.println("Got a response " + statusText);
    });
}).thenRun(() -> {
    try {
        client.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}).thenRun(system::terminate);

If you want to run WSClient standalone, but still use configuration (including SSL), you can use a configuration parser like this:

// Set up Akka
String name = "wsclient";
ActorSystem system = ActorSystem.create(name);
ActorMaterializerSettings settings = ActorMaterializerSettings.create(system);
ActorMaterializer materializer = ActorMaterializer.create(settings, system, name);

// Read in config file from application.conf
Config conf = ConfigFactory.load();
WSConfigParser parser = new WSConfigParser(conf, ClassLoader.getSystemClassLoader());
AhcWSClientConfig clientConf = AhcWSClientConfigFactory.forClientConfig(parser.parse());

// Start up asynchttpclient
final DefaultAsyncHttpClientConfig asyncHttpClientConfig = new AhcConfigBuilder(clientConf).configure().build();
final DefaultAsyncHttpClient asyncHttpClient = new DefaultAsyncHttpClient(asyncHttpClientConfig);

// Create a new WSClient, and then close the client.
WSClient client = new AhcWSClient(asyncHttpClient, materializer);
client.close();
system.terminate();

Again, once you are done with your custom client work, you must close the client, or you will leak threads:

try {
    customWSClient.close();
} catch (IOException e) {
    logger.error(e.getMessage(), e);
}

Ideally, you should only close a client after you know all requests have been completed. You should not use try-with-resources to automatically close a WSClient instance, because WSClient logic is asynchronous and try-with-resources only supports synchronous code in its body.

§Custom BodyReadables and BodyWritables

Play WS comes with rich type support for bodies in the form of play.libs.ws.WSBodyWritables, which contains methods for converting input such as JsonNode or XML in the body of a WSRequest into a ByteString or Source<ByteString, ?>, and play.libs.ws.WSBodyReadables, which contains methods that read the body of a WSResponse from a ByteString or Source[ByteString, _] and return the appropriate type, such as JsValue or XML. The default methods are available to you through the WSRequest and WSResponse, but you can also use custom types with response.getBody(myReadable()) and request.post(myWritable(data)). This is especially useful if you want to use a custom library, i.e. you would like to stream XML through STaX API.

§Creating a Custom Readable

You can create a custom readable by parsing the response:

public interface URLBodyReadables {
    default BodyReadable<java.net.URL> url() {
        return response -> {
            try {
                String s = response.getBody();
                return java.net.URI.create(s).toURL();
            } catch (MalformedURLException e) {
                throw new RuntimeException(e);
            }
        };
    }
}

§Creating a Custom BodyWritable

You can create a custom body writable to a request as follows, using an InMemoryBodyWritable. To specify a custom body writable with streaming, use a SourceBodyWritable.

public interface URLBodyWritables {
    default InMemoryBodyWritable body(java.net.URL url) {
        try {
            String s = url.toURI().toString();
            ByteString byteString = ByteString.fromString(s);
            return new InMemoryBodyWritable(byteString, "text/plain");
        } catch (URISyntaxException e) {
            throw new RuntimeException(e);
        }
    }
}

§Standalone WS

If you want to call WS outside of Play altogether, you can use the standalone version of Play WS, which does not depend on any Play libraries. You can do this by adding play-ahc-ws-standalone to your project:

libraryDependencies += "com.typesafe.play" %% "play-ahc-ws-standalone" % playWSStandalone

Please see https://github.com/playframework/play-ws and the 2.6 migration guide for more information.

§Accessing AsyncHttpClient

You can get access to the underlying shaded AsyncHttpClient from a WSClient.

play.shaded.ahc.org.asynchttpclient.AsyncHttpClient underlyingClient =
    (play.shaded.ahc.org.asynchttpclient.AsyncHttpClient) ws.getUnderlying();

§Configuring WS

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

• play.ws.followRedirects: Configures the client to follow 301 and 302 redirects (default is true).
• play.ws.useProxyProperties: To use the system http proxy settings(http.proxyHost, http.proxyPort) (default is true).
• play.ws.useragent: To configure the User-Agent header field.
• play.ws.compressionEnabled: Set it to true to use gzip/deflater encoding (default is false).

§Timeouts

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

• play.ws.timeout.connection: The maximum time to wait when connecting to the remote host (default is 120 seconds).
• play.ws.timeout.idle: The maximum time the request can stay idle (connection is established but waiting for more data) (default is 120 seconds).
• play.ws.timeout.request: The total time you accept a request to take (it will be interrupted even if the remote host is still sending data) (default is 120 seconds).

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

§Configuring WS with SSL

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

§Configuring WS with Caching

To configure WS for use with HTTP caching, please see Configuring WS Cache.

§Configuring AsyncClientConfig

The following advanced settings can be configured on the underlying AsyncHttpClientConfig.

Please refer to the AsyncHttpClientConfig Documentation for more information.

• play.ws.ahc.keepAlive
• play.ws.ahc.maxConnectionsPerHost
• play.ws.ahc.maxConnectionsTotal
• play.ws.ahc.maxConnectionLifetime
• play.ws.ahc.idleConnectionInPoolTimeout
• play.ws.ahc.maxNumberOfRedirects
• play.ws.ahc.maxRequestRetry
• play.ws.ahc.disableUrlEncoding

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