Refreshing OAuth token with okhttp interceptors. All requests will wait until token refresh finished, and then will continue with the new token.

Interceptor.java

private class HttpInterceptor implements Interceptor {

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

		//Build new request
		Request.Builder builder = request.newBuilder();
		builder.header("Accept", "application/json"); //if necessary, say to consume JSON
		
		String token = settings.getAccessToken(); //save token of this request for future
		setAuthHeader(builder, token); //write current token to request

		request = builder.build(); //overwrite old request
		Response response = chain.proceed(request); //perform request, here original request will be executed

		if (response.code() == 401) { //if unauthorized
			synchronized (httpClient) { //perform all 401 in sync blocks, to avoid multiply token updates
				String currentToken = settings.getAccessToken(); //get currently stored token

				if(currentToken != null && currentToken.equals(token)) { //compare current token with token that was stored before, if it was not updated - do update

					int code = refreshToken() / 100; //refresh token
					if(code != 2) { //if refresh token failed for some reason
						if(code == 4) //only if response is 400, 500 might mean that token was not updated
							logout(); //go to login screen
						return response; //if token refresh failed - show error to user
					}
				}

				if(settings.getAccessToken() != null) { //retry requires new auth token,
					setAuthHeader(builder, settings.getAccessToken()); //set auth token to updated
					request = builder.build();
					return chain.proceed(request); //repeat request with new token
				}
			}
		}

		return response;
	}
	
	private void setAuthHeader(Request.Builder builder, String token) {
		if (token != null) //Add Auth token to each request if authorized
			builder.header("Authorization", String.format("Bearer %s", token));
	}
	
	private int refreshToken() {
		//Refresh token, synchronously, save it, and return result code
		//you might use retrofit here
	}
	
	private int logout() {
		//logout your user
	}
}

This is very good. Thanks for sharing this.
Only issue with this implementation is after token gets refreshed, all other requests get executed in serial.
Is there a way to make execution of those requests parallel?

private int refreshToken() {
		//Refresh token, synchronously, save it, and return result code
		//you might use retrofit here
}

So you are proposing to use retrofit inside Interceptor to refresh token? This is quite ugly workaround.