As Cewolf uses a MVC (Model-View-Control) approach the data which +are shown in your chart are separated from the view defined in the JSP +page. So you can change them separately. To provide the chart with the +correct data you must provide an object which implements the interfacede.laures.cewolf.DatasetProducer. +This object is asked to produce data every time a new chart must be +rendered. Below you can see an example implementation of a +DatasetProducer which could be used to provide data needed for our +example scenario.
++
package de.laures.cewolf.example;
+
+import java.io.Serializable;
+import java.util.Date;
+import java.util.Map;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.jfree.data.category.CategoryDataset;
+import org.jfree.data.category.DefaultCategoryDataset;
+
+import de.laures.cewolf.DatasetProduceException;
+import de.laures.cewolf.DatasetProducer;
+import de.laures.cewolf.links.CategoryItemLinkGenerator;
+import de.laures.cewolf.tooltips.CategoryToolTipGenerator;
+
+/**
+ * An example data producer.
+ * @author Guido Laures
+ */
+public class PageViewCountData implements DatasetProducer, CategoryToolTipGenerator, CategoryItemLinkGenerator, Serializable {
+
+ private static final Log log = LogFactory.getLog(PageViewCountData.class);
+
+ // These values would normally not be hard coded but produced by
+ // some kind of data source like a database or a file
+ private final String[] categories = {"mon", "tue", "wen", "thu", "fri", "sat", "sun"};
+ private final String[] seriesNames = {"cewolfset.jsp", "tutorial.jsp", "testpage.jsp", "performancetest.jsp"};
+
+ /**
+ * Produces some random data.
+ */
+ public Object produceDataset(Map params) throws DatasetProduceException {
+ log.debug("producing data.");
+ DefaultCategoryDataset dataset = new DefaultCategoryDataset(){
+ /**
+ * @see java.lang.Object#finalize()
+ */
+ protected void finalize() throws Throwable {
+ super.finalize();
+ log.debug(this +" finalized.");
+ }
+ };
+ for (int series = 0; series < seriesNames.length; series ++) {
+ int lastY = (int)(Math.random() * 1000 + 1000);
+ for (int i = 0; i < categories.length; i++) {
+ final int y = lastY + (int)(Math.random() * 200 - 100);
+ lastY = y;
+ dataset.addValue(y, seriesNames[series], categories[i]);
+ }
+ }
+ return dataset;
+ }
+
+ /**
+ * This producer's data is invalidated after 5 seconds. By this method the
+ * producer can influence Cewolf's caching behaviour the way it wants to.
+ */
+ public boolean hasExpired(Map params, Date since) {
+ log.debug(getClass().getName() + "hasExpired()");
+ return (System.currentTimeMillis() - since.getTime()) > 5000;
+ }
+
+ /**
+ * Returns a unique ID for this DatasetProducer
+ */
+ public String getProducerId() {
+ return "PageViewCountData DatasetProducer";
+ }
+
+ /**
+ * Returns a link target for a special data item.
+ */
+ public String generateLink(Object data, int series, Object category) {
+ return seriesNames[series];
+ }
+
+ /**
+ * @see java.lang.Object#finalize()
+ */
+ protected void finalize() throws Throwable {
+ super.finalize();
+ log.debug(this + " finalized.");
+ }
+
+ /**
+ * @see org.jfree.chart.tooltips.CategoryToolTipGenerator#generateToolTip(CategoryDataset, int, int)
+ */
+ public String generateToolTip(CategoryDataset arg0, int series, int arg2) {
+ return seriesNames[series];
+ }
+
+}
+
+As you can see this datasetproducer is not very useful. Normally +this class would try to access a datasource (e.g. a database) to access +the needed information. But to serve as an example it should do.
+A DatasetProducer needs to implement three methods. The most +important one is the produceDataset() method which actually +produces the data which should be used to render a chart. This method +takes a parameter map which is filled by some special tags of the JSP +which will be explained later on.
+The hasExpired() method is called by the Cewolf framework +if there already exits a data object produced by this producer in +Cewolf's data cache. When returning true the producer +signalizes that the data formerly used has expired.
+By providing an unique ID via the getProducerId() method +the Cewolf framework identifies a producer type. Two producer instances +with the same ID are supposed to produce the same data.
+Compile the class and put it in the correct folder structure under +your web application's /WEB-INF/classes directory to make it +available for your application.
+Step 3: Install the Cewolf Servlet in your Web +Application>>
+