diff -r 000000000000 -r 639991d0808a java/cewolf-1.0/src/site/tutorial/step2.html --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/java/cewolf-1.0/src/site/tutorial/step2.html Sat Feb 28 21:31:02 2009 +0100 @@ -0,0 +1,138 @@ + + + + Cewolf Tutorial(2): Provide a DatasetProducer + + + + +

Tutorial: Step 2

+

Provide a DatasetProducer

+

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>>

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