TaskqueueServlet.java

/**
 * Copyright 2015 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.example.taskqueue;

import com.google.appengine.api.taskqueue.TaskOptions;
import com.google.appengine.api.taskqueue.Queue;
import com.google.appengine.api.taskqueue.QueueFactory;
import com.google.appengine.api.taskqueue.TaskHandle;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import java.util.Date;
import java.util.List;
import java.util.logging.Logger;
import java.util.concurrent.TimeUnit;

/**
 * Form Handling Servlet
 * This servlet has one method
 * {@link #doPost(<#HttpServletRequest req#>, <#HttpServletResponse resp#>)} which takes the form
 * submisson from /src/main/webapp/tasks.jsp to add and delete tasks.
 */
public class TaskqueueServlet extends HttpServlet {

   private static final Logger log = Logger.getLogger(TaskqueueServlet.class.getName());
   private static final int numberOfTasksToAdd = 100;
   private static final int numberOfTasksToLease = 100;
   private static boolean useTaggedTasks = true;
   private static String output;
   private static String message;

   // Process the http POST of the form
   @Override
   public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException,
       ServletException {
       if (req.getParameter("addTask") != null) {
         String content = req.getParameter("content");
         String output = String.format("Adding %d Tasks to the Task Queue with a payload of '%s'",
           numberOfTasksToAdd, content.toString());
         log.info(output.toString());

         // Add Tasks to Task Queue
         // [START get_queue]
         Queue q = QueueFactory.getQueue("pull-queue");
         // [END get_queue]
         if (!useTaggedTasks) {
           for (int i = 0; i < numberOfTasksToAdd; i++) {
              // [START add_task]
      	      q.add(TaskOptions.Builder.withMethod(TaskOptions.Method.PULL)
                                                   .payload(content.toString()));
              // [END add_task]
           }
         } else {
           for (int i = 0; i < numberOfTasksToAdd; i++) {
              // [START add_task_w_tag]
              q.add(TaskOptions.Builder.withMethod(TaskOptions.Method.PULL)
                                                .payload(content.toString())
                                                .tag("process".getBytes()));
              // [END add_task_w_tag]

           }
         }
         try {
           message = "Added " + numberOfTasksToAdd + " tasks to the task queue.";
           req.setAttribute("message", message);
           req.getRequestDispatcher("tasks.jsp").forward(req,resp);
         } catch (ServletException e) {
           throw new ServletException("ServletException error: ", e);
         }
       } else if (req.getParameter("leaseTask") != null) {
         output = String.format("Pulling %d Tasks from the Task Queue", numberOfTasksToLease);
         log.info(output.toString());

         // Pull tasks from the Task Queue and process them
         Queue q = QueueFactory.getQueue("pull-queue");
         if (!useTaggedTasks) {
           // [START lease_tasks]
           List<TaskHandle> tasks = q.leaseTasks(3600, TimeUnit.SECONDS, numberOfTasksToLease);
           // [END lease_tasks]
           message = processTasks(tasks, q);
         } else {
           // [START lease_tasks_by_tag]
           // Lease only tasks tagged with "process"
           List<TaskHandle> tasks = q.leaseTasksByTag(3600, TimeUnit.SECONDS, numberOfTasksToLease, "process");
           // You can also specify a tag to lease via LeaseOptions passed to leaseTasks.
           // [END lease_tasks_by_tag]
           message = processTasks(tasks, q);
         }
       req.setAttribute("message", message);
       req.getRequestDispatcher("tasks.jsp").forward(req,resp);
      } else {
        resp.sendRedirect("/");
      }
   }

   //Method to process and delete tasks
   private static String processTasks(List<TaskHandle> tasks, Queue q) {
     String payload;
     int numberOfDeletedTasks = 0;
     for (TaskHandle task : tasks) {
       payload = new String(task.getPayload());
       output = String.format("Processing: taskName='%s'  payload='%s'", task.getName()
         .toString(), payload.toString());
       log.info(output.toString());
       output = String.format("Deleting taskName='%s'", task.getName().toString());
       log.info(output.toString());
       // [START delete_task]
       q.deleteTask(task);
       // [END delete_task]
       numberOfDeletedTasks++;
     }
     if (numberOfDeletedTasks > 0) {
       message = "Processed and deleted " + numberOfTasksToLease + " tasks from the " +
         " task queue.";
     } else {
       message = "Task Queue has no tasks available for lease.";
     }
     return message;
   }
}