Tutorials : Using FOP with Java

Using FOP with Servlet

Web based applications often need to display different data and reports. Again, the same data may need to be formatted and presented differently to different users. In such contexts, FOP becomes very useful. We can maintain separate stylesheets for different display formats and can still reuse the same FOP formatting engine. Just to show how flexible it is to use FOP, we will write a Servlet which will use FOP to produce a PDF output of the Catalogue information XML (listing 1) and send it straight back to the browser.

The Servlet code is shown in Listing 3.

import org.apache.fop.apps.Driver;
import org.apache.fop.apps.XSLTInputHandler;
import org.apache.fop.render.Renderer;
import org.apache.avalon.framework.logger.Logger;
import org.apache.avalon.framework.logger.ConsoleLogger;
 
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import java.io.IOException;
import java.io.ByteArrayOutputStream;
import java.util.logging.Level;
 
 
public class FOPServlet extends HttpServlet
{
    private String xmlFile = "data.xml";
    private String xslFile = "pdfGen.xsl";
 
    protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse 
httpServletResponse) throws ServletException, IOException
    {
        // set up a FOP driver
        Driver driver = new Driver();
        // set up the logger for the driver
        Logger logger = new ConsoleLogger(ConsoleLogger.LEVEL_INFO);
        driver.setLogger(logger);
 
        try
        {
            //set the renderer to be PDF
            driver.setRenderer(Driver.RENDER_PDF);
 
            //create the input from the XSLT transform
            XSLTInputHandler inputHandler = new XSLTInputHandler(xmlFile, xslFile);
 
            // now prepare the outputStrean
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
 
            //set the driver outputStream
            driver.setOutputStream(outStream);
 
            //do the XSLT
            driver.render(inputHandler.getParser(), inputHandler.getInputSource());
 
            //now that the content is written in the output stream,
            //get ready to send the response back to browser
            byte[] content = outStream.toByteArray();
            httpServletResponse.setContentLength(content.length);
            // set the MIME-TYPE
            httpServletResponse.setContentType("application/pdf");
            //write the content
            httpServletResponse.getOutputStream().write(content);
            httpServletResponse.getOutputStream().flush();
 
        } catch (Exception e)
        {
            e.printStackTrace();
        }

    }
 
}

Few important things to notice in this code example.

• We start by creating a FOP Driver object and set the render type to be PDF. This lets FOP know that it has to produce a PDF output.
• We let the drive know about an OutputStream object to write the rendered content.
• We use the FOP XSLTInputHandler object to do the XSL transform by supplying it the xml file and the xsl file.
• Then, we ask the Driver object to render the document and pipe it to the specified OutputStream.
• Finally, before sending the response back to the browser, we set the MIME type to "application/pdf".

Following this example, it would be easy to convert this code to save the generated PDF output to a file in your hard drive. To do that, you just need to create a FileOutputStream object and set it to the Driver instead of the HTTP Response output stream. You will see a nice PDF file stored in the specified location.

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