Using JFreeCharts

[Steve Dyke]

Can someone help me with using the JFreeCharts in my JSP-Servlet Web App? Do I create a class for the generation of the chart, call it from my servlet, then display it on the JSP? I really need help with this.

[Ulf Dittmer]

The way to use JFreeChart in a web app is really by using of the cewolf tag library. Its web site has a tutorial that shows how to use the most important features.

[Steve Dyke]

This looks good. But every chart in my app will have to be printed to a pdf file. Can I do this with Cewolf charts?

[Ulf Dittmer]

No, I don't think there's anything PDF-related in JFreeChart. But once you have the rendered image you should be able to grab it from the session, save it to disk, and embed it in a PDF. The iText library makes this quite easy.

[Steve Dyke]

How do I go about grabing it from the session and saving it to disk? Also, I am using JasperReports for text reports. Can I use JasperReports to make the charts I save printable?

[Ulf Dittmer]

The basic way to grab an image from cewolf's session data is as follows. The "img" parameter is the same one that's used in the img tag that generates the chart.

The tricky part is to get at that "img" parameter. You could use the cewolf:imgurl tag to put the URL into a JavaScript variable, and then parse the "img=....." part out of it. Then you can write the link to the PDF in a JavaScript document.write statement. A hack, admittedly, but not hard to implement.

import de.laures.cewolf.*;
 
ServletConfig servletCfg  = ...;
 
// not sure if the following line is necessary
servletCfg.getServletContext().setAttribute("CewolfRenderer_Init_Config", servletCfg);
 
Configuration config = Configuration.getInstance(servletCfg.getServletContext());
 
String imgKey = request.getParameter("img");
if ( imgKey == null ) {
// no "img" parameter; do something about it
}
 
Storage storage = config.getStorage();
ChartImage chartImage = storage.getChartImage(imgKey, request);
 
if ( chartImage == null ) {
// image has expired, do something about it
} else {
// Now that we have a valid ChartImage object we can use its methods
// to determine the MIME type, width and height of the image, and get its bytes
}

Once you have the bytes of the image, you can iText's Image.getInstance() method to get an Image object that you can add to a Document.