Example 2 : Cached Stock pricing graph

Screenshot
Graph.html
Graph1.java

This is an example of how to cache sophisticated images

The free OOS library jCharts is used here to draw the graphs

The user can enter an arbitrary company name and hit the 'show stock graph' button.
The graph is cached application-wide with the key being the company name and the graph will expire 5 minutes after creation
During the 5 minutes caching time, repeated calls from the same browser with the same company name will not arrive at the server, because the image is cached on the browser.
See the jcharts with image maps example of how to add an image map to this same example >

Screenshot

Graph

Note

This is static documentation. You can see this example live

Graph.html

			
<form jwcid="@Form">
	Enter an arbitrary company name : <input type="text" jwcid="@TextField" 
	listener="listener:onSubmit" value="ognl:companyName"/>
	<input type="submit" value="show stock graph"/>   
</form>
		
<img jwcid="@sotacs:DynamicImage"  parameters="ognl:companyName"
	height="300" width="500" painter="painter:paintGraph" 
	cachingMode="literal:application"
	disabled="ognl:companyName == null || companyName.trim().length() == 0"
/>

Graph1.java

			
public abstract class Graph1 extends BasePage{
	
	private static final int MINUTES_BACK = 8;

	@Persist("client")
	public abstract String getCompanyName();
		
	/*
	* this method paints the graph and sets expiration time
	*/
	public void paintGraph(Graphics2D g2d, IPainterContext context){
		//retrieve data from DB
		double[] data = getStockData(getCompanyName());
		   
		//render the chart with jCharts
		try{
			Chart chart = makeJChart(context, data); 
			chart.setGraphics2D(g2d);
			chart.render();
		} catch(Throwable e){
			e.printStackTrace();
		}
	       
		//set expiration time to 5 minutes 
		context.setExpiresAt(System.currentTimeMillis() + 1000 * 60 * 5);
	}
	
	/*
	* Produce a chart using the jCharts-API
	*/   
	private Chart makeJChart(IPainterContext context, double[] data) 
				throws Exception{
		GregorianCalendar cal = new GregorianCalendar();
		   
		String[] xLabels = new String[MINUTES_BACK];
		   
		for (int i = MINUTES_BACK - 1; i >= 0 ;i--) {
			if(i != MINUTES_BACK - 1) cal.add(Calendar.MINUTE, -1);
			xLabels[i] = cal.get(Calendar.HOUR_OF_DAY) + "h " + 
				cal.get(Calendar.MINUTE );
		}
		String xTitle = "Time";
		String yTitle = "Price in $";
		String title = getCompanyName() + " (last updated "+ new Date()+")";
		DataSeries dataSeries = 
			new DataSeries( xLabels, xTitle, yTitle, title );
		String[] legendLabels = {getCompanyName() + " stock price"};
		Paint[] paints = new Paint[]{Color.BLUE};
		Stroke[] strokes= { new BasicStroke( 1.0f )};
		Shape[] shapes= { PointChartProperties.SHAPE_CIRCLE };
		LineChartProperties lineChartProperties = 
			new LineChartProperties(strokes, shapes);
		AxisChartDataSet axisChartDataSet = 
			new AxisChartDataSet(new double[][]{data}, legendLabels,
				paints, ChartType.LINE, lineChartProperties );
		dataSeries.addIAxisPlotDataSet( axisChartDataSet );
		ChartProperties chartProperties= new ChartProperties();
	
		AxisProperties axisProperties= new AxisProperties();
		LegendProperties legendProperties= new LegendProperties();

		return new AxisChart( dataSeries, chartProperties, 
					axisProperties, legendProperties, 
					context.getWidth(), context.getHeight());
		
	}

	/*
	 * retrieve stock prices out of a randomDB 
	 */
	private double[] getStockData(String name) {
		Random random = new Random(System.currentTimeMillis());
		double[] data = new double[MINUTES_BACK];
		double start = random.nextDouble() * 1000.0 + 1.0;
		for (int i = 0; i < data.length; i++) {
			start += start * 0.4 * random.nextGaussian();
			if(start < 0)  start = - start;
			data[i] = start;
		}
		return data;
	}

}