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1   /*
2    * JBoss, Home of Professional Open Source
3    * Copyright 2014, Red Hat, Inc. and/or its affiliates, and individual
4    * contributors by the @authors tag. See the copyright.txt in the
5    * distribution for a full listing of individual contributors.
6    *
7    * Licensed under the Apache License, Version 2.0 (the "License");
8    * you may not use this file except in compliance with the License.
9    * You may obtain a copy of the License at
10   * http://www.apache.org/licenses/LICENSE-2.0
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.jboss.as.quickstarts.servlet.async;
18  
19  import javax.inject.Inject;
20  import javax.servlet.AsyncContext;
21  import javax.servlet.annotation.WebServlet;
22  import javax.servlet.http.HttpServlet;
23  import javax.servlet.http.HttpServletRequest;
24  import javax.servlet.http.HttpServletResponse;
25  
26  /**
27   * <p>
28   * A simple asynchronous servlet taking advantage of features added in 3.0.
29   * </p>
30   * 
31   * <p>
32   * The servlet is registered and mapped to /AsynchronousServlet using the {@link WebServlet} annotation. The
33   * {@link LongRunningService} is injected by CDI.
34   * </p>
35   * 
36   * <p>
37   * It shows how to detach the execution of a long-running task from the request processing thread, so the thread is free to
38   * serve other client requests. The long-running tasks are executed using a dedicated thread pool and create the client response
39   * asynchronously using the {@link AsyncContext}.
40   * </p>
41   * 
42   * <p>
43   * A long-running task in this context does not refer to a computation intensive task executed on the same machine but could for
44   * example be contacting a third-party service that has limited resources or only allows for a limited number of concurrent
45   * connections. Moving the calls to this service into a separate and smaller sized thread pool ensures that less threads will be
46   * busy interacting with the long-running service and that more requests can be served that do not depend on this service.
47   * </p>
48   * 
49   * @author Christian Sadilek <csadilek@redhat.com>
50   */
51  @SuppressWarnings("serial")
52  @WebServlet(value = "/AsynchronousServlet", asyncSupported = true)
53  public class AsynchronousServlet extends HttpServlet {
54  
55      @Inject
56      private LongRunningService longRunningService;
57  
58      @Override
59      protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
60          // Here the request is put in asynchronous mode
61          AsyncContext asyncContext = req.startAsync();
62  
63          // This method will return immediately when invoked,
64          // the actual execution will run in a separate thread.
65          longRunningService.readData(asyncContext);
66      }
67  }