DatasetProducer


1   /* ================================================================
2    * Cewolf : Chart enabling Web Objects Framework
3    * ================================================================
4    *
5    * Project Info:  http://cewolf.sourceforge.net
6    * Project Lead:  Guido Laures (guido@laures.de);
7    *
8    * (C) Copyright 2002, by Guido Laures
9    *
10   * This library is free software; you can redistribute it and/or modify it under the terms
11   * of the GNU Lesser General Public License as published by the Free Software Foundation;
12   * either version 2.1 of the License, or (at your option) any later version.
13   *
14   * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
15   * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
16   * See the GNU Lesser General Public License for more details.
17   *
18   * You should have received a copy of the GNU Lesser General Public License along with this
19   * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
20   * Boston, MA 02111-1307, USA.
21   */
22  
23  package de.laures.cewolf;
24  
25  import java.io.Serializable  ;
26  import java.util.Date  ;
27  import java.util.Map  ;
28  
29  /**
30   * Produces a {@link org.jfree.data.Dataset} which will be rendered 
31   * as a chart   afterwards.
32   * @see org.jfree.data.Dataset
33   * @author  Guido Laures
34   * @since 0.1
35   */
36  public interface DatasetProducer extends Serializable   {
37      
38      /**
39       * By default the the name of the JSP attribute 
40       * holding the producer instance is passed to the 
41       * produceDataset method as a prameter.
42       */
43      public static final String   PRODUCER_ATTRIBUTE_NAME = "de.laures.cewolf.DatasetProducer.id";
44      
45      /**
46       * Produces a {@link org.jfree.data.Dataset} object.
47       * @param params additional params for the dataset production. All elements
48       * of this HashMap are of type <code>java.io.Serializable</code>. This is
49       * necessary to ensure the the serialization of the dataset producer into
50       * the http session. To provide a producer with additional production
51       * parameters the &lt;param&gt; tag is used (see tag library documentation).
52       * It is recommended to synchronize implementations of this method to avoid
53       * concurrency problems.
54       * @return an object of type <code>org.jfree.data.Dataset</code>.
55       * @throws DatasetProduceException if an error occured during production
56       * @since 0.2
57       */
58      Object   produceDataset(Map   params) throws DatasetProduceException;
59      
60      /**
61       * This method is called by the Cewolf framework to check if a formerly
62       * produced data can be reused. If the data which had already been used
63       * for chart rendering is still valid this method should return <code>true</code>.
64       * If possible the Cewolf framework will try to reuse the rendered chart
65       * image. If this is not possible because of some circumstances (e.g. the chart
66       * had been removed from the image cache) the produceDataset method is called afterwards.
67       * Therefore there is no guarantee that the dataset production is always 
68       * avoided if this method returns <code>true</true>.
69       * @param params the production parameters of the already produced data
70       * @param since the point in time when the already produced data had been produced
71       * @return <code>true</code> if the data which had been produced with the 
72       * passed in parameters has expired since its creation, <code>false</code> 
73       * otherwise
74       * @since 0.9
75       */
76      boolean hasExpired(Map   params, Date   since);
77      
78      /**
79       * Tis method returns a unique ID for a DatasetProducer from this class.
80       * Producers with the same ID are supposed to produce the same data when
81       * called with the same paramters.
82       * @return the unique ID for instances of this poducer class
83       * @since 0.9
84       */
85      String   getProducerId();
86  
87  }
88
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