AsyncRestServlet.java

/*
 * Copyright 2016 Google Inc.
 *
 * 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 com.google.appengine.demos.asyncrest;

import org.eclipse.jetty.client.HttpClient;
import org.eclipse.jetty.client.api.Response;
import org.eclipse.jetty.client.api.Result;
import org.eclipse.jetty.http.HttpMethod;
import org.eclipse.jetty.util.BufferUtil;
import org.eclipse.jetty.util.Utf8StringBuilder;
import org.eclipse.jetty.util.ajax.JSON;
import org.eclipse.jetty.util.ssl.SslContextFactory;

import java.io.IOException;
import java.io.PrintWriter;
import java.nio.ByteBuffer;
import java.util.Map;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicInteger;

import javax.servlet.AsyncContext;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet which makes REST calls asynchronously.
 *
 * <p>May be configured with init parameters:
 * <dl>
 * <dt>appid</dt>
 * <dd>The Google app key to use</dd>
 * </dl>
 *
 */
public class AsyncRestServlet extends AbstractRestServlet {

  static final String RESULTS_ATTR = "com.google.appengine.demos.asyncrest.client";
  static final String DURATION_ATTR = "com.google.appengine.demos.asyncrest.duration";
  static final String START_ATTR = "com.google.appengine.demos.asyncrest.start";

  HttpClient client;

  @Override
  public void init(ServletConfig servletConfig) throws ServletException {
    super.init(servletConfig);
    SslContextFactory sslContextFactory = new SslContextFactory();
    client = new HttpClient(sslContextFactory);

    try {
      client.start();
    } catch (Exception e) {
      throw new ServletException(e);
    }
  }

  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
          throws ServletException, IOException {

    if (key == null) {
      response.sendError(500, APPKEY + " not set");
      return;
    }

    Long start = System.nanoTime();

    // Do we have results yet?
    Queue<Map<String, Object>> results =
        (Queue<Map<String, Object>>) request.getAttribute(RESULTS_ATTR);

    // If no results, this must be the first dispatch, so send the REST request(s).
    if (results == null) {
      // define results data structures
      final Queue<Map<String, Object>> resultsQueue = new ConcurrentLinkedQueue<>();
      request.setAttribute(RESULTS_ATTR, results = resultsQueue);

      // Suspend the request.
      // This is done before scheduling async handling to avoid race of
      // dispatch before startAsync!
      final AsyncContext async = request.startAsync();
      async.setTimeout(30000);

      // Extract keywords to search for.
      String lat = sanitize(request.getParameter(LATITUDE_PARAM));
      String longitude = sanitize(request.getParameter(LONGITUDE_PARAM));
      String radius = sanitize(request.getParameter(RADIUS_PARAM));
      String[] keywords = sanitize(request.getParameter(ITEMS_PARAM)).split(",");

      final AtomicInteger outstanding = new AtomicInteger(keywords.length);

      // Send request each keyword.
      for (final String item : keywords) {
        client.newRequest(restQuery(lat + "," + longitude, radius, item))
            .method(HttpMethod.GET)
            .send(
                new AsyncRestRequest() {
                  @Override
                  void onLocationFound(Map<String, Object> result) {
                    resultsQueue.add(result);
                  }

                  @Override
                  void doComplete() {
                    if (outstanding.decrementAndGet() <= 0) {
                      async.dispatch();
                    }
                  }
                });
      }

      // save timing info and return
      request.setAttribute(START_ATTR, start);
      request.setAttribute(DURATION_ATTR, System.nanoTime() - start);

      return;
    }

    // We have results!
    // Generate the response
    String thumbs = generateResults(results);

    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out.println("<html><head>");
    out.println(STYLE);
    out.println("</head><body><small>");

    long initial = (Long) request.getAttribute(DURATION_ATTR);
    long start0 = (Long) request.getAttribute(START_ATTR);

    long now = System.nanoTime();
    long total = now - start0;
    long generate = now - start;
    long thread = initial + generate;

    String loc = sanitize(request.getParameter(LOC_PARAM));
    out.print(
        "<b>Asynchronous: Requesting " + sanitize(request.getParameter(ITEMS_PARAM)) + " near "
            + (loc != null ? loc
                    : "lat=" + sanitize(request.getParameter(LATITUDE_PARAM)) + " long="
                    + sanitize(request.getParameter(LONGITUDE_PARAM)))
            + "</b><br/>");
    out.print("Total Time: " + ms(total) + "ms<br/>");

    out.print(
        "Thread held (<span class='red'>red</span>): "
            + ms(thread) + "ms (" + ms(initial)
            + " initial + " + ms(generate) + " generate )<br/>");
    out.print("Async wait (<span class='green'>green</span>): " + ms(total - thread) + "ms<br/>");

    out.println(
        "<img border='0px' src='asyncrest/red.png' height='20px' width='" + width(initial) + "px'>"
            + "<img border='0px' src='asyncrest/green.png'"
            + " height='20px'"
            + " width='" + width(total - thread) + "px'>"
            + "<img border='0px' src='asyncrest/red.png'"
            + " height='20px'"
            + " width='" + width(generate) + "px'>");

    out.println("<br/>");
    out.print("First 5 results of " + results.size() + ":<br/>");
    if ("".equals(thumbs)) {
      out.print("<i>No results. Ensure " + APPKEY + " property is set correctly.</i>");
    } else {
      out.println(thumbs);
    }

    out.println("</small>");
    out.println("</body></html>");
    out.close();
  }

  private abstract class AsyncRestRequest extends Response.Listener.Adapter {

    final Utf8StringBuilder utf8Content = new Utf8StringBuilder();

    AsyncRestRequest() {
    }

    @Override
    public void onContent(Response response, ByteBuffer content) {
      byte[] bytes = BufferUtil.toArray(content);
      utf8Content.append(bytes, 0, bytes.length);
    }

    @Override
    public void onComplete(Result result) {
      // Extract results.
      Map<String, Object> data = (Map<String, Object>) JSON.parse(utf8Content.toString());
      if (data != null) {
        Object[] results = (Object[]) data.get("results");
        if (results != null) {
          for (Object o : results) {
            onLocationFound((Map<String, Object>) o);
          }
        }
      }
      doComplete();

    }

    abstract void onLocationFound(Map<String, Object> details);

    abstract void doComplete();

  }

  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
          throws ServletException, IOException {
    doGet(request, response);
  }
}