Exemplo de fila de tarefas do Java

Com o código a seguir, uma tarefa é adicionada a uma fila com opções.

No index.html:

<!-- A basic index.html file served from the "/" URL. -->
<html>
<body>
<p>Enqueue a value, to be processed by a worker.</p>
<form action="/enqueue" method="post">
    <input type="text" name="key">
    <input type="submit">
</form>
</body>
</html>

No Enqueue.java:

appengine-java8/taskqueues-push/src/main/java/com/example/appengine/taskqueue/push/Enqueue.java 
// The Enqueue servlet should be mapped to the "/enqueue" URL.
// With @WebServlet annotation the webapp/WEB-INF/web.xml is no longer required.
@WebServlet(
    name = "TaskEnque",
    description = "taskqueue: Enqueue a job with a key",
    urlPatterns = "/taskqueues/enqueue"
)
public class Enqueue extends HttpServlet {

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    String key = request.getParameter("key");

    // Add the task to the default queue.
    Queue queue = QueueFactory.getDefaultQueue();
    queue.add(TaskOptions.Builder.withUrl("/worker").param("key", key));

    response.sendRedirect("/");
  }
}

No Worker.java:

appengine-java8/taskqueues-push/src/main/java/com/example/appengine/taskqueue/push/Worker.java 
// The Worker servlet should be mapped to the "/worker" URL.
// With @WebServlet annotation the webapp/WEB-INF/web.xml is no longer required.
@WebServlet(
    name = "TaskWorker",
    description = "TaskQueues: worker",
    urlPatterns = "/taskqueues/worker"
)
public class Worker extends HttpServlet {

  private static final Logger log = Logger.getLogger(Worker.class.getName());

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    String key = request.getParameter("key");

    // Do something with key.
    // ...
  }
}

As tarefas adicionadas a essa fila são executadas chamando o gerenciador de solicitações no URL /worker com o parâmetro key. Elas são executadas com a taxa definida no arquivo queue.xml ou com a taxa padrão de cinco tarefas por segundo.