XSLT transformation from a servlet

[code]
package somepackage;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerFactoryConfigurationError;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.w3c.dom.Document;

/**
 * Generate servlet output based on XML input and an XSLT document.
 * filename, XML Document (DOM Object), and an optional contenttype
 * are to be passed in as requestparameters.
 * @author Jeroen Wenting
 */
public class Generator extends HttpServlet
{
	public static final String defContentType = "text/html; charset=UTF-8";
	public static final String contentTypeHTML = defContentType;
//	public static final String contentTypeXML = "text/xml; charset=UTF-8";
//	public static final String contentTypeCSV = "application/vnd.ms-excel";
	public static final String errorTemplate = "+++ERRORS+++";
	private static HashMap cache;
	/**
	 * 
	 */
	public Generator()
	{
		super();
	}
	
	/**
	 * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException
	{
		doPost(request, response);
	}

	/**
	 * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException
	{
		String contentType = null;
		Document doc = null;
		String xsl = null;
		
		contentType = (String)request.getAttribute("contenttype");
		if (contentType == null) contentType = defContentType;
		doc = (Document)request.getAttribute("xml-doc");
		xsl = (String)request.getAttribute("xsl-file-name");
		String path = getServletContext().getRealPath("/WEB-INF/xsl/");
		// Output goes in the response stream.
		PrintWriter out = response.getWriter();		
		
		if (doc == null || xsl == null)
		{
			String errorMsg = "";
			if (doc == null)
				errorMsg += "XML document missing from call to OutputGenerator<br />";
			if (xsl == null)
				errorMsg += "XSL filename missing from call to OutputGenerator<br />";
			StringBuffer buf = generateError(errorMsg);
			log(errorMsg);
			out.write(buf.toString());
			return;
		}
				
		// The servlet returns HTML.
		response.setContentType(contentType);    
		if (cache == null) cache = new HashMap();
		Transformer t = null;
		// Get the XML input document and the stylesheet.
		Source xmlSource = new DOMSource(doc);
		// Perform the transformation, sending the output to the response.
			
		// XSL processing can be time consuming, but this is mainly due to the overhead
		// of compiling the XSL sheet. 
		// By caching the compiled sheets, the process is speeded up dramatically.
		// Time saved on subsequent requests can be 99% or more (hundreds of milliseconds).	
		try
		{
			// check if the XSL sheet was found in cache, and use that if available
			if (cache.containsKey(xsl)) t = (Transformer)cache.get(xsl);
			else
			{
				// otherwise, load the XSL sheet from disk, compile it and store the compiled
				// sheet in the cache
				TransformerFactory tFactory = TransformerFactory.newInstance();
				Source xslSource = new StreamSource(new File(path, xsl+".xsl"));			
				t = tFactory.newTransformer(xslSource);
				cache.put(xsl, t);
			}
			// perform the XSL transformation of the XML Document into the servlet outputstream
			t.transform(xmlSource, new StreamResult(out));
		}
		catch (TransformerConfigurationException e)
		{
			e.printStackTrace();
			throw new ServletException(e);
		}
		catch (TransformerFactoryConfigurationError e)
		{
			e.printStackTrace();
			throw new ServletException(e);
		}
		catch (TransformerException e)
		{
			e.printStackTrace();
			throw new ServletException(e);
		}

	}

	private StringBuffer generateError(String error) throws IOException
	{
		
		String path = getServletContext().getRealPath("/WEB-INF/templates/");
		File f = new File(path, "callerror.html");
		FileInputStream fs = new FileInputStream(f);
		BufferedInputStream bis = new BufferedInputStream(fs);
		int numBytes = bis.available();
		byte b[] = new byte[numBytes];
		// read the template into a StringBuffer (via a byte array)
		bis.read(b);
		StringBuffer buf = new StringBuffer();
		buf.append(b);
		int start = buf.indexOf(errorTemplate);
		int end = start + errorTemplate.length();
		// replace placeholder with errormessage 
		// (will automatically adjust to take longer or shorter data into account)
		buf.replace(start, end, error);
		return buf;
	}	

}
[/code]

======================================================
Sample XSLT:

[code]
<?xml version="1.0"?> 
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

<xsl:import href="title.xsl" />

<xsl:output method="html" indent="yes"/>
	<xsl:template match="ehwa-doc">
		<html>
			<xsl:call-template name="title"/>
			<body><xsl:attribute name="onload"><xsl:apply-templates select="focuscontrol"/></xsl:attribute>
				<form>
					<input type="hidden" value="1" name="runset" id="runset"/>
				</form>
				<xsl:call-template name="hello"/>
			</body>
		</html>
	</xsl:template>

<xsl:template match="focuscontrol">
	<xsl:value-of select="."/>
</xsl:template>

<xsl:template name="hello">
	<xsl:value-of select="data" />
</xsl:template>

</xsl:stylesheet>
[/code]
======================================================
Error HTML template:

[code]
<?xml version="1.0"?> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 					  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-US"> 
<head>
<title></title>
</head>

<body> 
+++ERRORS+++
</body> 
</html>
[/code]

======================================================
Sample servlet to generate the XML and forward to the generator:

[code]
package somepackage;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.xerces.dom.DocumentImpl;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

/**
 * @author Jeroen Wenting
 */
public class XSLTest extends HttpServlet
{

	/**
	 * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
	 */
	protected void doGet(HttpServletRequest arg0, HttpServletResponse arg1)
		throws ServletException, IOException
	{
		doPost(arg0, arg1);
	}

	/**
	 * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException
	{
		String xslFilename = getInitParameter("xslfile-html");
		String beanName = getInitParameter("formbean");
		String contentType = getInitParameter("contenttype");
		request.setAttribute("xsl-file-name", xslFilename);
		if (contentType != null) request.setAttribute("contenttype", contentType);
		Document doc = new DocumentImpl();

		Element root = doc.createElement("ehwa-doc");

		// generate XML for transformation
		Element elem = doc.createElement("focuscontrol");
		elem.appendChild(doc.createTextNode("alert('loaded')"));
		root.appendChild(elem);
		elem = doc.createElement("data");
		elem.appendChild(doc.createTextNode("Hello World!"));
		root.appendChild(elem);		
		
		doc.appendChild(root);		
		request.setAttribute("xml-doc", doc);
		RequestDispatcher rd = request.getRequestDispatcher("/servlet/generator");
		rd.forward(request, response);
	}


}
[/code]