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1   package org.apache.turbine.modules.screens;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  
22  import org.apache.ecs.ConcreteElement;
23  import org.apache.turbine.modules.Screen;
24  import org.apache.turbine.util.RunData;
25  
26  /***
27   * Base class for writing Screens that output binary data.  This class
28   * is provided as a helper class for those who want to write Screens
29   * that output raw binary data.  For example, it may be extended into
30   * a Screen that outputs a SVG file or a SWF (Flash Player format)
31   * movie.  The only thing one has to do is to implement the two
32   * methods <code>getContentType(RunData data)</code> and
33   * <code>doOutput(RunData data)</code> (see below).
34   *
35   * <p> You migth want to take a look at the ImageServer screen class
36   * contained in the TDK.<br>
37   *
38   * @author <a href="mailto:rkoenig@chez.com">Regis Koenig</a>
39   * @version $Id: RawScreen.java 534527 2007-05-02 16:10:59Z tv $
40   */
41  public abstract class RawScreen extends Screen
42  {
43      /***
44       * Build the Screen.  This method actually makes a call to the
45       * doOutput() method in order to generate the Screen content.
46       *
47       * @param data Turbine information.
48       * @return A ConcreteElement.
49       * @exception Exception, a generic exception.
50       */
51      protected final ConcreteElement doBuild(RunData data)
52              throws Exception
53      {
54          data.getResponse().setContentType(getContentType(data));
55          data.declareDirectResponse();
56          doOutput(data);
57          return null;
58      }
59  
60      /***
61       * Set the content type.  This method should be overidden to
62       * actually set the real content-type header of the output.
63       *
64       * @param data Turbine information.
65       * @return A String with the content type.
66       */
67      protected abstract String getContentType(RunData data);
68  
69      /***
70       * Actually output the dynamic content.  The OutputStream can be
71       * accessed like this: <pre>OutputStream out =
72       * data.getResponse().getOutputStream();</pre>.
73       *
74       * @param data Turbine information.
75       * @exception Exception, a generic exception.
76       */
77      protected abstract void doOutput(RunData data)
78              throws Exception;
79  
80      /***
81       * The layout must be set to null.
82       *
83       * @param data Turbine information.
84       * @return A null String.
85       */
86      public final String getLayout(RunData data)
87      {
88          return null;
89      }
90  }