source: main/trunk/greenstone3/src/java/org/greenstone/gsdl3/util/XMLTransformer.java@ 22370

/*
 *    XMLTransformer.java
 *    Copyright (C) 2002 New Zealand Digital Library, http://www.nzdl.org
 *
 *    This program is free software; you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation; either version 2 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package org.greenstone.gsdl3.util;

// XML classes
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.ErrorListener;

import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.dom.DOMResult;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Element;
import org.w3c.dom.Document;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

// other java classes
import java.io.StringReader;
import java.io.StringWriter;
import java.io.File;
import java.util.HashMap;
import java.util.Set;
import java.util.Map;
import java.util.Iterator;

import org.apache.xml.utils.DefaultErrorHandler;

import org.apache.log4j.*;

/** XMLTransformer - utility class for greenstone
 *
 * transforms xml using xslt
 *
 * @author <a href="mailto:[email protected]">Katherine Don</a>
 * @version $Revision: 22370 $
 */
public class XMLTransformer {

    static Logger logger = Logger.getLogger(org.greenstone.gsdl3.util.XMLTransformer.class.getName());
    
  /** The transformer factory we're using */
    TransformerFactory t_factory=null;
  
  /**
   * The no-arguments constructor. 
   *
   * Any exceptions thrown are caught internally
   * 
   * @see javax.xml.transform.TransformerFactory
   */
    public XMLTransformer() {
    // make sure we are using the xalan transformer

    // http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/api/index.html?javax/xml/transform/TransformerFactory.html states that
    // TransformerFactory.newInstance() looks in jar files for a Factory specified in META-INF/services/javax.xml.transform.TransformerFactory, 
    // else it will use the "platform default"
    // In this case: xalan.jar's META-INF/services/javax.xml.transform.TransformerFactory contains org.apache.xalan.processor.TransformerFactoryImpl
    // as required.

    // This means we no longer have to do a System.setProperty("javax.xml.transform.TransformerFactory", "org.apache.xalan.processor.TransformerFactoryImpl");
    // followed by a this.t_factory = org.apache.xalan.processor.TransformerFactoryImpl.newInstance();
    // The System.setProperty step to force the TransformerFactory implementation that gets used conflicts with
    // Fedora (visiting the Greenstone server pages breaks the Greenstone-tomcat hosted Fedora pages) as Fedora 
    // does not include the xalan.jar and therefore can't then find the xalan TransformerFactory explicitly set.

    try {
        this.t_factory = TransformerFactory.newInstance();
    } catch (Exception e) {
        logger.error("exception "+e.getMessage());
    }
    }

 
    
  /**
   * Transform an XML document using a XSLT stylesheet
   * 
   * @param stylesheet a filename for an XSLT stylesheet
   * @param xml_in the XML to be transformed
   * @return the transformed XML
   */
    public String transform(String stylesheet, String xml_in) {
    
    try {
        // Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
        Transformer transformer = this.t_factory.newTransformer(new StreamSource(stylesheet));
        transformer.setErrorListener(new TransformErrorListener());

        // Use the Transformer to transform an XML Source and send the output to a Result object.
        StringWriter output = new StringWriter();

        transformer.transform(new StreamSource(new StringReader(xml_in)), new StreamResult(output));
        return output.toString();
    } catch (TransformerConfigurationException e) {
        logger.error("couldn't create transformer object: "+e.getMessageAndLocation());
        logger.error(e.getLocationAsString());  
        return "";
    } catch (TransformerException e) {
        logger.error("couldn't transform the source: " + e.getMessageAndLocation());
        return "";
    }   
    }

    public String transformToString(Document stylesheet, Document source) {
    return transformToString(stylesheet, source, null);
    }
    
    public String transformToString(Document stylesheet, Document source, HashMap parameters) {
    
    try {
        // Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
        Transformer transformer = this.t_factory.newTransformer(new DOMSource(stylesheet));
        transformer.setErrorListener(new TransformErrorListener());
        if (parameters != null) {
        Set params = parameters.entrySet();
        Iterator i = params.iterator();
        while (i.hasNext()) {
            Map.Entry m = (Map.Entry)i.next();
            transformer.setParameter((String)m.getKey(), m.getValue());
        }
        }
        //transformer.setParameter("page_lang", source.getDocumentElement().getAttribute(GSXML.LANG_ATT));

        
        // Use the Transformer to transform an XML Source and send the output to a Result object.
        StringWriter output = new StringWriter();
        
        transformer.transform(new DOMSource(source), new StreamResult(output));
        return output.toString();
    } catch (TransformerConfigurationException e) {
        logger.error("couldn't create transformer object: "+e.getMessageAndLocation());
        logger.error(e.getLocationAsString());  
        return "";
    } catch (TransformerException e) {
        logger.error("couldn't transform the source: " + e.getMessageAndLocation());
        return "";
    }
    }

    public Node transform(Document stylesheet, Document source) {
    return transform(stylesheet, source, null, null);
    }

    public Node transform(Document stylesheet, Document source, HashMap parameters, Document docDocType) {
        try {
            // Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
            Transformer transformer = this.t_factory.newTransformer(new DOMSource(stylesheet));
            transformer.setErrorListener(new TransformErrorListener());
            if (parameters != null) {
                Set params = parameters.entrySet();
                Iterator i = params.iterator();
                while (i.hasNext()) {
                    Map.Entry m = (Map.Entry)i.next();
                    transformer.setParameter((String)m.getKey(), m.getValue());
                }
            }

            // When we transform the DOMResult, we need to make sure the result of
            // the transformation has a DocType. For that to happen, we need to create
            // the DOMResult using a Document with a predefined docType.
            // If we don't have a DocType then do the transformation with a DOMResult
            // that does not contain any doctype (like we use to do before).
            DOMResult result = docDocType == null ? new DOMResult() : new DOMResult(docDocType);
            transformer.transform(new DOMSource(source), result);
            return result.getNode(); // pass the entire document
        } 
        catch (TransformerConfigurationException e) {
            return transformError("XMLTransformer.transform(Doc, Doc, HashMap, Doc)"
                + "\ncouldn't create transformer object", e);
        } 
        catch (TransformerException e) {
            return transformError("XMLTransformer.transform(Doc, Doc, HashMap, Doc)"
                + "\ncouldn't transform the source", e);
        }
    }

    public Node transform(File stylesheet, File source) {
    try {
        Transformer transformer = this.t_factory.newTransformer(new StreamSource(stylesheet));
        transformer.setErrorListener(new TransformErrorListener());
        DOMResult result = new DOMResult();
        transformer.transform(new StreamSource(source), result);
        return result.getNode().getFirstChild();
    } catch (TransformerConfigurationException e) {
            return transformError("XMLTransformer.transform(File, File)"
                + "\ncouldn't create transformer object for files\n" 
                + stylesheet + "\n" + source, e);
    } 
    catch (TransformerException e) {
        return transformError("XMLTransformer.transform(File, File)"
                + "\ncouldn't transform the source for files\n" 
                + stylesheet + "\n" + source, e);
    }   
 }
 
    public Node transform(File stylesheet, File source, Document docDocType) {
        try {
            Transformer transformer = this.t_factory.newTransformer(new StreamSource(stylesheet));
            transformer.setErrorListener(new TransformErrorListener());
            DOMResult result = new DOMResult(docDocType);
            transformer.transform(new StreamSource(source), result);
            return result.getNode().getFirstChild();
        } catch (TransformerConfigurationException e) {
            return transformError("XMLTransformer.transform(File, File, Doc)"
                + "\ncouldn't create transformer object for files\n" 
                + stylesheet + "\n" + source, e);
        } 
        catch (TransformerException e) {
            return transformError("XMLTransformer.transform(File, File, Doc)"
                + "\ncouldn't transform the source for files\n" 
                + stylesheet + "\n" + source, e);
        }   
    }
    
    // Given a heading string on the sort of transformation error that occurred and the exception object itself, 
    // this method prints the exception to the tomcat window (system.err) and the greenstone log and then returns
    // an xhtml error page that is constructed from it.
    protected Node transformError(String heading, TransformerException e) {
        String message = heading + "\n" + e.getMessage();
        logger.error(heading + ": " + e.getMessage());
        
        String location = e.getLocationAsString();      
        if(location != null) {
            logger.error(location);
            message = message + "\n" + location;
        }
        System.err.println("****\n" + message + "\n****");
        return constructErrorXHTMLPage(message);
    }
    
    // Given an error message, splits it into separate lines based on any newlines present and generates an xhtml page
    // (xml Element)  with paragraphs for each line. This is then returned so that it can be displayed in the browser.
    public static Element constructErrorXHTMLPage(String message) {
        try{
            String[] lines = message.split("\n");
        
            Document xhtmlDoc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
            // <html></html>
            Node htmlNode = xhtmlDoc.createElement("html");
            xhtmlDoc.appendChild(htmlNode);
            // <head></head>
            Node headNode = xhtmlDoc.createElement("head");
            htmlNode.appendChild(headNode);
            // <title></title>
            Node titleNode = xhtmlDoc.createElement("title");
            headNode.appendChild(titleNode);
            Node titleString = xhtmlDoc.createTextNode("Error occurred");
            titleNode.appendChild(titleString);
            
            // <body></body>
            Node bodyNode = xhtmlDoc.createElement("body");
            htmlNode.appendChild(bodyNode);
            
            // finally put the message in the body
            Node h1Node = xhtmlDoc.createElement("h1");
            bodyNode.appendChild(h1Node);
            Node headingString = xhtmlDoc.createTextNode("The following error occurred:");
            h1Node.appendChild(headingString);
            
            //Node textNode = xhtmlDoc.createTextNode(message);
            //bodyNode.appendChild(textNode);
            
            for (int i = 0; i < lines.length; i++) {
                Node pNode = xhtmlDoc.createElement("p");
                Node textNode = xhtmlDoc.createTextNode(lines[i]);
                pNode.appendChild(textNode);
                bodyNode.appendChild(pNode);
            }
            
            return xhtmlDoc.getDocumentElement();
            
        }catch(Exception e) {
            String errmsg = "Exception trying to construct error xhtml page from message: " + message
                + "\n" + e.getMessage();
            System.err.println(errmsg);
            logger.error(errmsg);
            return null;
        }
    }
    
    // ErrorListener class that can be used to register a handler for any fatal errors, errors and warnings that may
    // occur when transforming an xml file with an xslt stylesheet. The errors are printed both to the greenstone.log and 
    // to the tomcat console (System.err), and the error message is stored in the errorMessage variable so that it can
    // be retrieved and be used to generate an xhtml error page.
    static public class TransformErrorListener implements ErrorListener {
        protected String errorMessage = null;
    
        //  Receive notification of a recoverable error.
        public void error(TransformerException exception) {
            handleError("Error:\n", exception);
        }
        //   Receive notification of a non-recoverable error.
        public void fatalError(TransformerException exception) {
            handleError("Fatal Error:\n", exception);
        }
        // Receive notification of a warning.
        public void warning(TransformerException exception) {
            handleError("Warning:\n", exception);
        }
        
        public String toString(TransformerException e) {
            String location = e.getLocationAsString();
            if(location == null) {
                return e.getMessage();
            }
            return e.getMessage() + "\n" + location;
        }
        
        // clears the errorPage variable after first call to this method
        public String getErrorMessage() {
            String errMsg = this.errorMessage;
            if(this.errorMessage != null) {
                this.errorMessage = null;
            }
            return errMsg;
        }
        
        // sets the errorMessage member variable to the data stored in the exception
        // and writes the errorMessage to the logger and tomcat's System.err
        protected void handleError(String errorType, TransformerException exception) {
            this.errorMessage = errorType + toString(exception); 
            System.err.println("\n****Error transforming xml:\n" + this.errorMessage + "\n****\n");
            logger.error(this.errorMessage);
        }
    }
}