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1.4 +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
1.5 +<html>
1.6 +<head>
1.7 + <title>Cewolf Tutorial(2): Provide a DatasetProducer</title>
1.8 + <meta name="author" content="Guido Laures">
1.9 + <link href="../cewolf.css" rel="stylesheet" type="text/css">
1.10 +</head>
1.11 +<body>
1.12 +<h1>Tutorial: Step 2</h1>
1.13 +<h2>Provide a DatasetProducer</h2>
1.14 +<p> As Cewolf uses a MVC (Model-View-Control) approach the data which
1.15 +are shown in your chart are separated from the view defined in the JSP
1.16 +page. So you can change them separately. To provide the chart with the
1.17 +correct data you must provide an object which implements the interface<tt>de.laures.cewolf.DatasetProducer</tt>.
1.18 +This object is asked to produce data every time a new chart must be
1.19 +rendered. Below you can see an example implementation of a
1.20 +DatasetProducer which could be used to provide data needed for our
1.21 +example scenario. </p>
1.22 +<p> </p>
1.23 +<pre>package de.laures.cewolf.example;
1.24 +
1.25 +import java.io.Serializable;
1.26 +import java.util.Date;
1.27 +import java.util.Map;
1.28 +
1.29 +import org.apache.commons.logging.Log;
1.30 +import org.apache.commons.logging.LogFactory;
1.31 +import org.jfree.data.category.CategoryDataset;
1.32 +import org.jfree.data.category.DefaultCategoryDataset;
1.33 +
1.34 +import de.laures.cewolf.DatasetProduceException;
1.35 +import de.laures.cewolf.DatasetProducer;
1.36 +import de.laures.cewolf.links.CategoryItemLinkGenerator;
1.37 +import de.laures.cewolf.tooltips.CategoryToolTipGenerator;
1.38 +
1.39 +/**
1.40 + * An example data producer.
1.41 + * @author Guido Laures
1.42 + */
1.43 +public class PageViewCountData implements DatasetProducer, CategoryToolTipGenerator, CategoryItemLinkGenerator, Serializable {
1.44 +
1.45 + private static final Log log = LogFactory.getLog(PageViewCountData.class);
1.46 +
1.47 + // These values would normally not be hard coded but produced by
1.48 + // some kind of data source like a database or a file
1.49 + private final String[] categories = {"mon", "tue", "wen", "thu", "fri", "sat", "sun"};
1.50 + private final String[] seriesNames = {"cewolfset.jsp", "tutorial.jsp", "testpage.jsp", "performancetest.jsp"};
1.51 +
1.52 + /**
1.53 + * Produces some random data.
1.54 + */
1.55 + public Object produceDataset(Map params) throws DatasetProduceException {
1.56 + log.debug("producing data.");
1.57 + DefaultCategoryDataset dataset = new DefaultCategoryDataset(){
1.58 + /**
1.59 + * @see java.lang.Object#finalize()
1.60 + */
1.61 + protected void finalize() throws Throwable {
1.62 + super.finalize();
1.63 + log.debug(this +" finalized.");
1.64 + }
1.65 + };
1.66 + for (int series = 0; series < seriesNames.length; series ++) {
1.67 + int lastY = (int)(Math.random() * 1000 + 1000);
1.68 + for (int i = 0; i < categories.length; i++) {
1.69 + final int y = lastY + (int)(Math.random() * 200 - 100);
1.70 + lastY = y;
1.71 + dataset.addValue(y, seriesNames[series], categories[i]);
1.72 + }
1.73 + }
1.74 + return dataset;
1.75 + }
1.76 +
1.77 + /**
1.78 + * This producer's data is invalidated after 5 seconds. By this method the
1.79 + * producer can influence Cewolf's caching behaviour the way it wants to.
1.80 + */
1.81 + public boolean hasExpired(Map params, Date since) {
1.82 + log.debug(getClass().getName() + "hasExpired()");
1.83 + return (System.currentTimeMillis() - since.getTime()) > 5000;
1.84 + }
1.85 +
1.86 + /**
1.87 + * Returns a unique ID for this DatasetProducer
1.88 + */
1.89 + public String getProducerId() {
1.90 + return "PageViewCountData DatasetProducer";
1.91 + }
1.92 +
1.93 + /**
1.94 + * Returns a link target for a special data item.
1.95 + */
1.96 + public String generateLink(Object data, int series, Object category) {
1.97 + return seriesNames[series];
1.98 + }
1.99 +
1.100 + /**
1.101 + * @see java.lang.Object#finalize()
1.102 + */
1.103 + protected void finalize() throws Throwable {
1.104 + super.finalize();
1.105 + log.debug(this + " finalized.");
1.106 + }
1.107 +
1.108 + /**
1.109 + * @see org.jfree.chart.tooltips.CategoryToolTipGenerator#generateToolTip(CategoryDataset, int, int)
1.110 + */
1.111 + public String generateToolTip(CategoryDataset arg0, int series, int arg2) {
1.112 + return seriesNames[series];
1.113 + }
1.114 +
1.115 +}
1.116 +</pre>
1.117 +<p> As you can see this datasetproducer is not very useful. Normally
1.118 +this class would try to access a datasource (e.g. a database) to access
1.119 +the needed information. But to serve as an example it should do. </p>
1.120 +<p> A DatasetProducer needs to implement three methods. The most
1.121 +important one is the <tt>produceDataset()</tt> method which actually
1.122 +produces the data which should be used to render a chart. This method
1.123 +takes a parameter map which is filled by some special tags of the JSP
1.124 +which will be explained later on. </p>
1.125 +<p> The <tt>hasExpired()</tt> method is called by the Cewolf framework
1.126 +if there already exits a data object produced by this producer in
1.127 +Cewolf's data cache. When returning <tt>true</tt> the producer
1.128 +signalizes that the data formerly used has expired. </p>
1.129 +<p> By providing an unique ID via the <tt>getProducerId()</tt> method
1.130 +the Cewolf framework identifies a producer type. Two producer instances
1.131 +with the same ID are supposed to produce the same data. </p>
1.132 +<p> Compile the class and put it in the correct folder structure under
1.133 +your web application's <tt>/WEB-INF/classes</tt> directory to make it
1.134 +available for your application. </p>
1.135 +<p> <a href="step3.html">Step 3: Install the Cewolf Servlet in your Web
1.136 +Application>></a> </p>
1.137 +<a height="30" target="new" href="http://sourceforge.net"><img
1.138 + alt="SourceForge Logo" border="0" height="30"
1.139 + src="http://sourceforge.net/sflogo.php?group_id=57282&type=5"></a>
1.140 +</body>
1.141 +</html>