Ръководство за OkHttp

Програмиране

1. Въведение

В тази статия, ние ще показваме основите на изпращане на различни видове на HTTP заявки, приемане и тълкуване на HTTP отговора , и как да се конфигурира клиент с OkHttp.

Освен това ще разгледаме по-напреднали случаи на конфигуриране на клиент с персонализирани заглавки, изчаквания, кеширане на отговори и т.н.

2. Общ преглед на OkHttp

OkHttp е ефективен HTTP & HTTP / 2 клиент за приложения за Android и Java.

Той се предлага с усъвършенствани функции като обединяване на връзки (ако HTTP / 2 не е налице), прозрачно GZIP компресиране и кеширане на отговори, за да се избегне изцяло мрежата за повтарящи се заявки.

Също така е в състояние да се възстанови от често срещани проблеми с връзката и при неуспех на връзката, ако услугата има множество IP адреси, тя може да опита отново заявката за алтернативни адреси.

На високо ниво клиентът е проектиран както за блокиране на синхронни, така и на неблокиращи асинхронни повиквания.

OkHttp поддържа Android 2.3 и по-нови версии. За Java минималното изискване е 1.7.

След този кратък преглед, нека видим някои примери за използване.

3. Зависимост на Maven

Нека първо добавим библиотеката като зависимост в pom.xml :

 com.squareup.okhttp3 okhttp 3.4.2

За да видите последната зависимост на тази библиотека, вижте страницата в Maven Central.

4. Синхронно GET с OkHttp

За да изпратим синхронна GET заявка, трябва да изградим обект Request въз основа на URL и да осъществим повикване . След неговото изпълнение получаваме обратно екземпляр на Response :

@Test public void whenGetRequest_thenCorrect() throws IOException { Request request = new Request.Builder() .url(BASE_URL + "/date") .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

5. Асинхронен GET с OkHttp

Сега, за да осъществим асинхронен GET, трябва да поставим Обаждане в опашката . А обратно обаждане ни позволява да прочетете отговора, когато то е разбираемо. Това се случва, след като заглавките на отговорите са готови.

Четенето на тялото на отговора все още може да блокира. Понастоящем OkHttp не предлага асинхронни API за получаване на тяло на отговор на части:

@Test public void whenAsynchronousGetRequest_thenCorrect() { Request request = new Request.Builder() .url(BASE_URL + "/date") .build(); Call call = client.newCall(request); call.enqueue(new Callback() { public void onResponse(Call call, Response response) throws IOException { // ... } public void onFailure(Call call, IOException e) { fail(); } }); }

6. ВЗЕМЕТЕ С Параметри на заявката

И накрая, за да добавим параметри на заявката към нашата GET заявка, можем да се възползваме от HttpUrl.Builder .

След изграждането на URL адреса можем да го предадем на нашия обект Request :

@Test public void whenGetRequestWithQueryParameter_thenCorrect() throws IOException { HttpUrl.Builder urlBuilder = HttpUrl.parse(BASE_URL + "/ex/bars").newBuilder(); urlBuilder.addQueryParameter("id", "1"); String url = urlBuilder.build().toString(); Request request = new Request.Builder() .url(url) .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

7. Искане след публикуване

Нека разгледаме проста POST заявка, където изграждаме RequestBody за изпращане на параметрите „потребителско име“ и „парола“ :

@Test public void whenSendPostRequest_thenCorrect() throws IOException { RequestBody formBody = new FormBody.Builder() .add("username", "test") .add("password", "test") .build(); Request request = new Request.Builder() .url(BASE_URL + "/users") .post(formBody) .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

Нашата статия Кратко ръководство за публикуване на заявки с OkHttp има още примери за POST заявки с OkHttp.

8. Качване на файл

8.1. Качи файл

В този пример ще видим как да качим файл . Ще качите " test.ext" файла с помощта MultipartBody.Builder :

@Test public void whenUploadFile_thenCorrect() throws IOException { RequestBody requestBody = new MultipartBody.Builder() .setType(MultipartBody.FORM) .addFormDataPart("file", "file.txt", RequestBody.create(MediaType.parse("application/octet-stream"), new File("src/test/resources/test.txt"))) .build(); Request request = new Request.Builder() .url(BASE_URL + "/users/upload") .post(requestBody) .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

8.2. Вземете напредък при качване на файлове

И накрая, нека видим как да постигнем напредъка при качване на файл . Ще разширим RequestBody, за да получим видимост в процеса на качване.

First, here’s the upload method:

@Test public void whenGetUploadFileProgress_thenCorrect() throws IOException { RequestBody requestBody = new MultipartBody.Builder() .setType(MultipartBody.FORM) .addFormDataPart("file", "file.txt", RequestBody.create(MediaType.parse("application/octet-stream"), new File("src/test/resources/test.txt"))) .build(); ProgressRequestWrapper.ProgressListener listener = (bytesWritten, contentLength) -> { float percentage = 100f * bytesWritten / contentLength; assertFalse(Float.compare(percentage, 100) > 0); }; ProgressRequestWrapper countingBody = new ProgressRequestWrapper(requestBody, listener); Request request = new Request.Builder() .url(BASE_URL + "/users/upload") .post(countingBody) .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

Here is the interface ProgressListener that enables us to observe the upload progress:

public interface ProgressListener { void onRequestProgress(long bytesWritten, long contentLength); }

Here is the ProgressRequestWrapper which is the extended version of RequestBody:

public class ProgressRequestWrapper extends RequestBody { @Override public void writeTo(BufferedSink sink) throws IOException { BufferedSink bufferedSink; countingSink = new CountingSink(sink); bufferedSink = Okio.buffer(countingSink); delegate.writeTo(bufferedSink); bufferedSink.flush(); } }

Finally, here is the CountingSink which is the extended version of ForwardingSink :

protected class CountingSink extends ForwardingSink { private long bytesWritten = 0; public CountingSink(Sink delegate) { super(delegate); } @Override public void write(Buffer source, long byteCount) throws IOException { super.write(source, byteCount); bytesWritten += byteCount; listener.onRequestProgress(bytesWritten, contentLength()); } }

Note that:

  • When extending ForwardingSink to “CountingSink”, we are overriding the write() method to count the written (transferred) bytes
  • When extending RequestBody to “ProgressRequestWrapper “, we are overriding the writeTo() method to use our “ForwardingSink”

9. Setting a Custom Header

9.1. Setting a Header on a Request

To set any custom header on a Request we can use a simple addHeader call:

@Test public void whenSetHeader_thenCorrect() throws IOException { Request request = new Request.Builder() .url(SAMPLE_URL) .addHeader("Content-Type", "application/json") .build(); Call call = client.newCall(request); Response response = call.execute(); response.close(); }

9.2. Setting a Default Header

In this example, we will see how to configure a default header on the Client itself, instead of setting it on each and every request.

For example, if we want to set a content type “application/json” for every request we need to set an interceptor for our client. Here is the method:

@Test public void whenSetDefaultHeader_thenCorrect() throws IOException { OkHttpClient client = new OkHttpClient.Builder() .addInterceptor( new DefaultContentTypeInterceptor("application/json")) .build(); Request request = new Request.Builder() .url(SAMPLE_URL) .build(); Call call = client.newCall(request); Response response = call.execute(); response.close(); }

And here is the DefaultContentTypeInterceptor which is the extended version of Interceptor:

public class DefaultContentTypeInterceptor implements Interceptor { public Response intercept(Interceptor.Chain chain) throws IOException { Request originalRequest = chain.request(); Request requestWithUserAgent = originalRequest .newBuilder() .header("Content-Type", contentType) .build(); return chain.proceed(requestWithUserAgent); } }

Note that the interceptor adds the header to the original request.

10. Do Not Follow Redirects

In this example, we'll see how to configure the OkHttpClient to stop following redirects.

By default, if a GET request is answered with an HTTP 301 Moved Permanently the redirect is automatically followed. In some use cases, that may be perfectly fine, but there are certainly use cases where that’s not desired.

To achieve this behavior, when we build our client, we need to set followRedirects to false.

Note that the response will return an HTTP 301 status code:

@Test public void whenSetFollowRedirects_thenNotRedirected() throws IOException { OkHttpClient client = new OkHttpClient().newBuilder() .followRedirects(false) .build(); Request request = new Request.Builder() .url("//t.co/I5YYd9tddw") .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(301)); }

If we turn on the redirect with a true parameter (or remove it completely), the client will follow the redirection and the test will fail as the return code will be an HTTP 200.

11. Timeouts

Use timeouts to fail a call when its peer is unreachable. Network failures can be due to client connectivity problems, server availability problems, or anything between. OkHttp supports connect, read, and write timeouts.

In this example, we built our client with a readTimeout of 1 seconds, while the URL is served with 2 seconds of delay:

@Test public void whenSetRequestTimeout_thenFail() throws IOException { OkHttpClient client = new OkHttpClient.Builder() .readTimeout(1, TimeUnit.SECONDS) .build(); Request request = new Request.Builder() .url(BASE_URL + "/delay/2") .build(); Call call = client.newCall(request); Response response = call.execute(); assertThat(response.code(), equalTo(200)); }

Note as the test will fail as the client timeout is lower than the resource response time.

12. Canceling a Call

Use Call.cancel() to stop an ongoing call immediately. If a thread is currently writing a request or reading a response, an IOException will be thrown.

Use this to conserve the network when a call is no longer necessary; for example when your user navigates away from an application:

@Test(expected = IOException.class) public void whenCancelRequest_thenCorrect() throws IOException { ScheduledExecutorService executor = Executors.newScheduledThreadPool(1); Request request = new Request.Builder() .url(BASE_URL + "/delay/2") .build(); int seconds = 1; long startNanos = System.nanoTime(); Call call = client.newCall(request); executor.schedule(() -> { logger.debug("Canceling call: " + (System.nanoTime() - startNanos) / 1e9f); call.cancel(); logger.debug("Canceled call: " + (System.nanoTime() - startNanos) / 1e9f); }, seconds, TimeUnit.SECONDS); logger.debug("Executing call: " + (System.nanoTime() - startNanos) / 1e9f); Response response = call.execute(); logger.debug(Call was expected to fail, but completed: " + (System.nanoTime() - startNanos) / 1e9f, response); }

13. Response Caching

To create a Cache, we'll need a cache directory that we can read and write to, and a limit on the cache's size.

The client will use it to cache the response:

@Test public void whenSetResponseCache_thenCorrect() throws IOException { int cacheSize = 10 * 1024 * 1024; File cacheDirectory = new File("src/test/resources/cache"); Cache cache = new Cache(cacheDirectory, cacheSize); OkHttpClient client = new OkHttpClient.Builder() .cache(cache) .build(); Request request = new Request.Builder() .url("//publicobject.com/helloworld.txt") .build(); Response response1 = client.newCall(request).execute(); logResponse(response1); Response response2 = client.newCall(request).execute(); logResponse(response2); }

After launching the test, the response from the first call will not have been cached. A call to the method cacheResponse will return null, while a call to the method networkResponse will return the response from the network.

Also, the cache folder will be filled with the cache files.

The second call execution will produce the opposite effect, as the response will have already been cached. This means that a call to networkResponse will return null while a call to cacheResponse will return the response from the cache.

To prevent a response from using the cache, use CacheControl.FORCE_NETWORK. To prevent it from using the network, use CacheControl.FORCE_CACHE.

Be warned: if you use FORCE_CACHE and the response requires the network, OkHttp will return a 504 Unsatisfiable Request response.

14. Conclusion

In this article, we have seen several examples of how to use OkHttp as an HTTP & HTTP/2 client.

Както винаги, примерният код може да бъде намерен в проекта GitHub.