Interceptors are used to intercept OkHttp calls. The reason to intercept could be to monitor, rewrite and retry calls. It can be used for outgoing request or incoming response both.

class LoggingInterceptor implements Interceptor {
  @Override public Response intercept(Interceptor.Chain chain) throws IOException {
    Request request = chain.request();

    long t1 = System.nanoTime();
    logger.info(String.format("Sending request %s on %s%n%s",
        request.url(), chain.connection(), request.headers()));

    Response response = chain.proceed(request);

    long t2 = System.nanoTime();
    logger.info(String.format("Received response for %s in %.1fms%n%s",
        response.request().url(), (t2 - t1) / 1e6d, response.headers()));

    return response;
  }
}

private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() {
  @Override public Response intercept(Interceptor.Chain chain) throws IOException {
    Response originalResponse = chain.proceed(chain.request());
    return originalResponse.newBuilder()
        .header("Cache-Control", "max-age=60")
        .build();
  }
};

I like to wrap my OkHttp into a class called HttpClient for example, and in this class I have methods for each of the major HTTP verbs, post, get, put and delete, most commonly. (I usually include an interface, in order to keep for it to implement, in order to be able to easily change to a different implementation, if need be):

public class HttpClient implements HttpClientInterface{

private static final String TAG = OkHttpClient.class.getSimpleName();
public static final MediaType JSON
        = MediaType.parse("application/json; charset=utf-8");

OkHttpClient httpClient = new OkHttpClient();

@Override
public String post(String url, String json) throws IOException {
    Log.i(TAG, "Sending a post request with body:\n" + json + "\n to URL: " + url);

    RequestBody body = RequestBody.create(JSON, json);
    Request request = new Request.Builder()
            .url(url)
            .post(body)
            .build();
    Response response = httpClient.newCall(request).execute();
    return response.body().string();
}

The syntax is the same for put, get and delete except for 1 word (.put(body)) so it might be obnoxious to post that code as well. Usage is pretty simple, just call the appropriate method on some url with some json payload and the method will return a string as a result that you can later use and parse. Let's assume that the response will be a json, we can create a JSONObject easily from it:

String response = httpClient.post(MY_URL, JSON_PAYLOAD);
JSONObject json = new JSONObject(response);
// continue to parse the response according to it's structure

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url(yourUrl)
        .build();

    Response response = client.newCall(request).execute();
    if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

    Headers responseHeaders = response.headers();

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

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url(yourUrl)
        .build();

    client.newCall(request).enqueue(new Callback() {
      @Override public void onFailure(Call call, IOException e) {
        e.printStackTrace();
      }

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

        Headers responseHeaders = response.headers();

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

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    RequestBody formBody = new FormBody.Builder()
        .add("search", "Jurassic Park")
        .build();
    Request request = new Request.Builder()
        .url("https://en.wikipedia.org/w/index.php")
        .post(formBody)
        .build();

    Response response = client.newCall(request).execute();
    if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

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

 private static final String IMGUR_CLIENT_ID = "...";
  private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");

  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    // Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image
    RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("title", "Square Logo")
        .addFormDataPart("image", "logo-square.png",
            RequestBody.create(MEDIA_TYPE_PNG, new File("website/static/logo-square.png")))
        .build();

    Request request = new Request.Builder()
        .header("Authorization", "Client-ID " + IMGUR_CLIENT_ID)
        .url("https://api.imgur.com/3/image")
        .post(requestBody)
        .build();

    Response response = client.newCall(request).execute();
    if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

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

Grab via Maven:

<dependency>
  <groupId>com.squareup.okhttp3</groupId>
  <artifactId>okhttp</artifactId>
  <version>3.6.0</version>
</dependency>

or Gradle:

compile 'com.squareup.okhttp3:okhttp:3.6.0'