code: /*
   * Copyright 2015 Google Inc. All rights reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.physical_web.collection;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.HttpURLConnection;
  import java.net.MalformedURLException;
  import java.net.URL;
  
  /**
   * A class that represents an http request.
   * This is to be used as a base class for more specific request classes.
   * @param <T> The type representing the request payload.
   */
  abstract class Request<T> extends Thread {
    private URL mUrl;
    private RequestCallback<T> mCallback;
  
    /**
     * Construct a Request object.
     * @param url The url to make an HTTP request to.
     * @param callback The callback run when the HTTP response is received.
     * @throws MalformedURLException on invalid url
     */
    public Request(String url, RequestCallback<T> callback) throws MalformedURLException {
      mUrl = new URL(url);
      mCallback = callback;
    }
  
    /**
     * The callback that gets run after the request is made.
     */
    public interface RequestCallback<T> {
      /**
       * The callback run on a valid response.
       * @param result The result object.
       */
      void onResponse(T result);
  
      /**
       * The callback run on an Exception.
       * @param httpResponseCode The HTTP response code.  This will be 0 if no
       *        response was received.
       * @param e The encountered Exception.
       */
      void onError(int httpResponseCode, Exception e);
    }
  
    /**
     * Make the HTTP request and parse the HTTP response.
     */
    @Override
    public void run() {
      // Setup some values
      HttpURLConnection urlConnection = null;
      T result = null;
      InputStream inputStream = null;
      int responseCode = 0;
      IOException ioException = null;
  
      // Make the request
      try {
        urlConnection = (HttpURLConnection) mUrl.openConnection();
        writeToUrlConnection(urlConnection);
        responseCode = urlConnection.getResponseCode();
        inputStream = new BufferedInputStream(urlConnection.getInputStream());
        result = readInputStream(inputStream);
      } catch (IOException e) {
        ioException = e;
      } finally {
        if (urlConnection != null) {
          urlConnection.disconnect();
        }
      }
  
      // Call the callback
      if (ioException == null) {
        mCallback.onResponse(result);
      } else {
        mCallback.onError(responseCode, ioException);
      }
    }
  
    /**
     * Helper method to make an HTTP request.
     * @param urlConnection The HTTP connection.
     * @throws IOException on error
     */
    protected abstract void writeToUrlConnection(HttpURLConnection urlConnection) throws IOException;
  
    /**
     * Helper method to read an HTTP response.
     * @param is The InputStream.
     * @return An object representing the HTTP response.
     * @throws IOException on error
     */
    protected abstract T readInputStream(InputStream is) throws IOException;
  }
  