Using OkHttp

Overview

OkHttp is a third-party library developed by Square for sending and receive HTTP-based network requests. It is built on top of the Okio library, which tries to be more efficient about reading and writing data than the standard Java I/O libraries by creating a shared memory pool.

The OkHttp library actually provides an implementation of the HttpUrlConnection interface. Android 4.4 and later versions now use this implementation, so the manual approach described in this section actually uses the OkHttp library. However, there is a separate API provided by OkHttp that makes it easier to send and receive network requests, which is described in this guide.

In addition, OkHttp v2.4 also provides a more updated way of managing URLs internally. Instead of the java.net.URL, java.net.URI, or android.net.Uri classes, it provides a new HttpUrl class that makes it easier to get an HTTP port, parse URLs, and canonicalizing URL strings.

Setup

Makes sure to enable the use of the Internet permission in your AndroidManifest.xml file:

<uses-permission android:name="android.permission.INTERNET"/>

Simply add this line to your app/build.gradle file:

compile 'com.squareup.okhttp:okhttp:2.5.0'

Sending and Receiving Network Requests

First, we must instantiate an OkHttpClient and create a Request object:

OkHttpClient client = new OkHttpClient();

Request request = new Request.Builder()
                     .url("http://publicobject.com/helloworld.txt")
                     .build();

Synchronous network calls

We can create a Call object and dispatch the network request synchronously:

Response response = client.newCall(request).execute();

Because Android disallows network calls on the main thread, you can only make synchronous calls if you do so on a separate thread or a background service. You can use also use AsyncTask for lightweight network calls.

Assuming the response returns, we can check whether it was successful and parse the response headers and body:

if (!response.isSuccessful()) {
  throw new IOException("Unexpected code " + response);
} 

Headers responseHeaders = response.headers();
for (int i = 0; i < responseHeaders.size(); i++) {
  System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
}

System.out.println(response.body().string());
}

Asynchronous network calls

We can also make asynchronous network calls too by creating a Call object, using the enqueue() method, and passing an anonymous Callback object that implements both onFailure() and onResponse().

// Get a handler that can be used to post to the main thread
client.newCall(request).enqueue(new Callback() {

@Override
public void onFailure(Request request, IOException e) {
  e.printStackTrace();
}

@Override
public void onResponse(final Response response) throws IOException {
  if (!response.isSuccessful()) {
     throw new IOException("Unexpected code " + response);
  }
}

OkHttp normally creates a new worker thread to dispatch the network request and uses the same thread to handle the response. Note that if you need to update any views, you can only make these updates on the main UI thread. Therefore, you will need to use runOnUiThread() or post the result back on the main thread:

@Override
public void onResponse(final Response response) throws IOException {
if (!response.isSuccessful()) {
  throw new IOException("Unexpected code " + response);
}

MainActivity.this.runOnUiThread(new Runnable() {
  @Override
  public void run() {
    try {
       TextView myTextView = ((TextView) (findViewById(R.id.myTextView)));
       myTextView.setText(response.body().string());
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
});

Check out Square's official recipe guide for other examples.

References

• Android’s HTTP Clients - Android Developers blog, September 29, 2011
• https://www.reddit.com/r/androiddev/comments/29p3zz/til_okhttp_engine_is_backing_httpurlconnection_as/
• https://github.com/square/okhttp/blob/master/okhttp-urlconnection/src/main/java/com/squareup/okhttp/internal/huc/HttpURLConnectionImpl.java
• https://speakerdeck.com/jakewharton/a-few-ok-libraries-droidcon-mtl-2015
• https://github.com/square/okio#sources-and-sink
• http://stackoverflow.com/questions/24246783/okhttp-response-callbacks-on-the-main-thread
• https://github.com/square/okhttp/wiki/Recipes
• https://twitter.com/jakewharton/status/482563299511250944