Jpanel to a picture in Servlet without saving to disk

Question

Hi. I need to display a graph on the fly in a servlet. I currently have the graph in a JPanel. I saw all the posts about how to save this to disk. Can anyone please suggest a way to display it (servlet generated HTML) without saving it to disk?
Any suggestions for a good tutorial on servlets serving generated images would also be highly appreciated.
Thank you very much,
Arijit

Answer 1

Hi,
I have an example that works with Java Server Faces based web components and produces svg dynamically. The same strategy can be used for jpg or any other graphical format.
* SessionServlet.java
* Created on June 3, 2004, 12:09 AM
package com.hypernex.xml.svg;
import java.io.*;
import java.net.*;
import javax.servlet.*;
import javax.servlet.http.*;
* @author  hyperdev
* @version
public class SessionServlet extends HttpServlet
    /** Initializes the servlet.
    public void init(ServletConfig config) throws ServletException
        super.init(config);
    /** Destroys the servlet.
    public void destroy()
    /** Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
        ServletContext context=getServletContext();
        java.util.Enumeration e=context.getServlets();
        while(e.hasMoreElements())
            System.out.println("servlets \t"+e.nextElement());
        /*e=context.getAttributeNames();
        while(e.hasMoreElements())
            System.out.println("AttributeNames \t"+e.nextElement());
        e=request.getParameterNames();
        while(e.hasMoreElements())
            System.out.println("ParameterNames \t"+e.nextElement());
        System.out.println("getContextPath "+request.getContextPath());
        System.out.println("getRequestURI"+request.getRequestURI());
        response.setContentType("text/xml+svg");
        PrintWriter out = response.getWriter();
        HttpSession httpSession=request.getSession();
        System.out.println("getQueryString"+httpSession);
        if(httpSession!=null && request.getRequestURI().endsWith("wafermap.svg"))
            /*e=httpSession.getAttributeNames();
            while(e.hasMoreElements())
                System.out.println("httpSession AttributeNames \t"+e.nextElement());
            SVGProducer svgProducer=(SVGProducer)httpSession.getAttribute("waferMap");
            out.print(svgProducer.getSVGView());
        else if(httpSession!=null && request.getRequestURI().endsWith("hardware.svg"))
            SVGProducer svgProducer=(SVGProducer)httpSession.getAttribute("hardwareBean");
            out.print(svgProducer.getSVGView());
        else if(httpSession!=null && request.getRequestURI().endsWith("geometry.svg"))
            SVGProducer svgProducer=(SVGProducer)httpSession.getAttribute("geometryBean");
            out.print(svgProducer.getSVGView());
        else
            try
                java.io.BufferedReader br=new java.io.BufferedReader(new java.io.FileReader("./webapps"+request.getRequestURI()));
                String line=null;
                while((line=br.readLine())!=null)
                    out.println(line);
                br.close();
            catch(java.io.IOException ioe)
                System.out.println("ioe:"+ioe.getMessage());
        out.close();
    /** Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
        processRequest(request, response);
    /** Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
        processRequest(request, response);
    /** Returns a short description of the servlet.
    public String getServletInfo()
        return "SVG graphics handler";
}And any jsf component that implements
* SVGProducer.java
* Created on June 3, 2004, 9:09 PM
package com.hypernex.xml.svg;
* @author  hyperdev
public interface SVGProducer
    public String getSVGView();
}such as
public class WaferMap extends Object implements com.hypernex.xml.svg.SVGProducer
    protected void generateSVGWafermap(java.sql.ResultSet resultSet)
        //FacesContext context = FacesContext.getCurrentInstance();
        //context.
        //Create an svg graph of the equation.
        org.apache.batik.dom.svg.SAXSVGDocumentFactory svgFactory=new org.apache.batik.dom.svg.SAXSVGDocumentFactory("org.apache.xerces.parsers.SAXParser");
        org.apache.batik.dom.svg.SVGDOMImplementation svgDOMImplementation=new org.apache.batik.dom.svg.SVGDOMImplementation();
        org.w3c.dom.DocumentType dt=null;//svgDOMImplementation.createDocumentType("svg","-//W3C//DTD SVG 1.1//EN",f.toURI().toString());
        //System.out.println(dt);
        org.w3c.dom.svg.SVGDocument svgOMDocument=null;
        try
            System.out.println("dir "+(new java.io.File(".")).toURI().toString());
            java.io.File f=new java.io.File("./webapps/jsf-wita/siteadmin/templates/wafermap-template.svg");
            svgOMDocument=(org.w3c.dom.svg.SVGDocument)svgFactory.createDocument(f.toURI().toString(), new java.io.FileInputStream(f));//new org.apache.batik.dom.svg.SVGOMDocument(dt, (org.w3c.dom.DOMImplementation)svgDOMImplementation);
            org.w3c.dom.svg.SVGSVGElement root=svgOMDocument.getRootElement();
            org.w3c.dom.svg.SVGGElement visuals=(org.w3c.dom.svg.SVGGElement)svgOMDocument.getElementById("visuals");
            //visuals.getFirstChild().setNodeValue(Double.toString(xMin));
            //resultSet.beforeFirst();
            while(resultSet.next())
                org.apache.batik.dom.svg.SVGOMRectElement rect=new org.apache.batik.dom.svg.SVGOMRectElement("", (org.apache.batik.dom.AbstractDocument)svgOMDocument);
                rect.setAttribute("fill", "teal");
                rect.setAttribute("stroke", "teal");
                rect.setAttribute("transform", "scale(1, -1)");
                rect.setAttribute("stroke-width", "1");
                double x=50+100.0*(resultSet.getDouble("X")-2.5)/300.0;
                double y=100.0*((resultSet.getDouble("Y")-2.0)/300.0-0.5);
                //System.out.println(x+" "+y);
                rect.setAttribute("x", Double.toString(x)+"%");
                rect.setAttribute("y", Double.toString(y)+"%");
                rect.setAttribute("width", "10");
                rect.setAttribute("height", "8");
                visuals.appendChild(rect);
            javax.xml.transform.TransformerFactory tFactory = javax.xml.transform.TransformerFactory.newInstance();
            javax.xml.transform.Transformer intermediateTransformer=tFactory.newTransformer(new javax.xml.transform.stream.StreamSource("./webapps/jsf-wita/stylesheets/identity.xsl"));
            java.io.CharArrayWriter caw=new java.io.CharArrayWriter();
            intermediateTransformer.transform(new javax.xml.transform.dom.DOMSource(svgOMDocument), new javax.xml.transform.stream.StreamResult(caw));
            svgView=caw.toString();
        catch(java.sql.SQLException sqle)
            System.out.println("sqle err: "+sqle.getMessage());
        catch(javax.xml.transform.TransformerConfigurationException tce)
            System.out.println("tce err: "+tce.getMessage());
        catch(javax.xml.transform.TransformerException te)
            System.out.println("te err: "+te.getMessage());
        catch(java.io.FileNotFoundException fnfe)
            System.out.println("fnfe:"+fnfe.getMessage());
        catch(java.io.IOException ioe)
            System.out.println("io:"+ioe.getMessage());
    public String getSVGView()
        return svgView;
    private String svgView="";of course with jpg or other binary formats you would need to use a byte array instead of a string. Note that my example does take a template svg file which holds all the static parts and positions for dynamic parts, gets any changes from the data in a database, and creates an in memory svg to go to the client with any changes since the last request.
On a jsf/jsp/html page where there is
<embed src="../wafermap.svg" align="left" width="400" height="400" ...the server will supply the graphic via the SessionServlet