guide-to-okhttp
A Guide to OkHttp
1. Introduction
In this article, we’ll show the basics of sending different types of HTTP requests, receiving and interpreting HTTP responses, and how to configure a Client with OkHttp.
Also, we’ll go into more advanced use cases of configuring a client with custom headers, timeouts, response caching, etc.
2. OkHttp Overview
It comes with advanced features such as connection pooling (if HTTP/2 isn’t available), transparent GZIP compression, and response caching to avoid the network completely for repeated requests.
It’s also able to recover from common connection problems and, on a connection failure, if a service has multiple IP addresses, it can retry the request to alternate addresses.
At a high level, the client is designed for both blocking synchronous and nonblocking asynchronous calls.
OkHttp supports Android 2.3 and above. For Java, the minimum requirement is 1.7.
After this brief overview, let’s see some usage examples.
3. Maven Dependency
<dependency>
<groupId>com.squareup.okhttp3</groupId>
<artifactId>okhttp</artifactId>
<version>3.4.2</version>
</dependency>To see the latest dependency of this library check out the page on Maven Central.
4. Synchronous GET with OkHttp
To send a synchronous GET request we need to build a Request object based on a URL and make a Call. After its execution we get back an instance of 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. Asynchronous GET with OkHttp
Now, to make an asynchronous GET we need to enqueue a Call. A Callback allows us to read the response when it is readable. This happens after the response headers are ready.
Reading the response body may still block. OkHttp doesn’t currently offer any asynchronous APIs to receive a response body in parts:
@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. GET with Query Parameters
After the URL is built we can pass it to our Request object:
@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. Post Request Example
In this simple example, we build a RequestBody to send two parameters – “username” and “password” – with the POST request:
@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));
}7.2. POST with Authorization
In this example, we’ll see how to do a POST with Basic Authentication credentials, plus we send a String as the body of the request:
@Test
public void whenSendPostRequestWithAuthorization_thenCorrect()
throws IOException {
String postBody = "test post";
Request request = new Request.Builder()
.url(URL_SECURED_BY_BASIC_AUTHENTICATION)
.addHeader("Authorization", Credentials.basic("test", "test"))
.post(RequestBody.create(
MediaType.parse("text/x-markdown; charset=utf-8"), postBody))
.build();
Call call = client.newCall(request);
Response response = call.execute();
assertThat(response.code(), equalTo(200));
}7.3. POST with JSON
@Test
public void whenPostJson_then:Correct() throws IOException {
String json = "{\"id\":1,\"name\":\"John\"}";
RequestBody body = RequestBody.create(
MediaType.parse("application/json; charset=utf-8"), json);
Request request = new Request.Builder()
.url(BASE_URL + "/users/detail")
.post(body)
.build();
Call call = client.newCall(request);
Response response = call.execute();
assertThat(response.code(), equalTo(200));
}7.4. Multipart POST Request
In this example, we’ll send a POST Multipart Request. We need to build our RequestBody as MultipartBody to post a File, a username, and a password:
@Test
public void whenSendMultipartRequest_thenCorrect()
throws IOException {
RequestBody requestBody = new MultipartBody.Builder()
.setType(MultipartBody.FORM)
.addFormDataPart("username", "test")
.addFormDataPart("password", "test")
.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/multipart")
.post(requestBody)
.build();
Call call = client.newCall(request);
Response response = call.execute();
assertThat(response.code(), equalTo(200));
}8. File Uploading
In this example, we’ll see how to upload a File. We’ll upload the “test.ext” file using 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. Get File Upload Progress
Finally, let’s see how to get the progress of a File upload. We’ll extend RequestBody to gain visibility into the upload process.
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
@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
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("https://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("https://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
As always, the example code can be found in the GitHub project.
