source: main/trunk/greenstone3/src/java/org/greenstone/gsdl3/util/XMLConverter.java@ 25265

/*
 *    XMLConverter.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 org.w3c.dom.DOMImplementation;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentType;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.NamedNodeMap;
import org.xml.sax.InputSource;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXParseException;
import org.apache.xerces.parsers.DOMParser;
import org.apache.xerces.dom.*; // for new Documents

// other java classes
import java.io.Reader;
import java.io.InputStreamReader;
import java.io.StringReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.util.regex.*;

import org.apache.log4j.*;

// Apache Commons
import org.apache.commons.lang3.*;

import java.util.*;
import java.lang.reflect.*;

/**
 * XMLConverter - utility class for greenstone
 * 
 * parses XML Strings into Documents, converts Nodes to Strings different
 * parsers have different behaviour - can experiment in here now we only use
 * xerces
 * 
 */
public class XMLConverter
{

    static Logger logger = Logger.getLogger(org.greenstone.gsdl3.util.XMLConverter.class.getName());

    protected EntityResolver resolver = null;
    
    /** xerces parser */
    protected DOMParser parser = null;

    private static boolean outputEscaping = true;

    /** the no-args constructor */
    public XMLConverter()
    {
        try
        {
            this.parser = new DOMParser();
            this.parser.setFeature("http://xml.org/sax/features/validation", false);
            // don't try and load external DTD - no need if we are not validating, and may cause connection errors if a proxy is not set up.
            this.parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
            // a performance test showed that having this on lead to increased 
            // memory use for small-medium docs, and not much gain for large 
            // docs.
            // http://www.sosnoski.com/opensrc/xmlbench/conclusions.html
            this.parser.setFeature("http://apache.org/xml/features/dom/defer-node-expansion", false);
            // add an errorhandler to the parser which will store useful a error message on encountering fatal errors, errors and warnings when parsing
            // this errormessage can then be converted to xhtml and displayed in a browser.
            this.parser.setErrorHandler(new ParseErrorHandler());
        }
        catch (Exception e)
        {
            logger.error(e.getMessage());
        }
    }

    /** sets the entity resolver. pass in null to unset it */
    public void setEntityResolver(EntityResolver er)
    {
        this.resolver = er;
        this.parser.setEntityResolver(er);
    }

    /**
     * Given a Node representing an Element or Document, will return the
     * Element/docroot Element. Returns null if the Node was not an element.
     */
    public static Element nodeToElement(Node node)
    {
        if (node == null)
        {
            return null;
        }
        short nodeType = node.getNodeType();

        if (nodeType == Node.DOCUMENT_NODE)
        {
            Document docNode = (Document) node;
            return docNode.getDocumentElement();
        }
        else if (nodeType == Node.ELEMENT_NODE)
        {
            return (Element) node;
        }
        else
        {
            String message = "Expecting Document or Element node type but got " + node.getNodeName() + "\nReturning null";
            System.err.println(message);
            logger.warn(message);
            return null;
        }
    }

    /** returns a DOM Document */
    public Document getDOM(String in)
    {

        try
        {
            Reader reader = new StringReader(in);
            InputSource xml_source = new InputSource(reader);

            DOMParser parser = new DOMParser();
            parser.setFeature("http://xml.org/sax/features/validation", false);
            parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
            parser.setFeature("http://apache.org/xml/features/dom/defer-node-expansion", false);
            if(resolver != null)
            {
                parser.setEntityResolver(this.resolver);
            }
            parser.setErrorHandler(new ParseErrorHandler());
            parser.parse(xml_source);
            
            Document doc = parser.getDocument();

            return doc;

        }
        catch (Exception e)
        {
            logger.error(e.getMessage());
        }
        return null;
    }

    /** returns a DOM Document */
    public Document getDOM(File in)
    {
        try
        {
            FileReader reader = new FileReader(in);
            InputSource xml_source = new InputSource(reader);
            
            DOMParser parser = new DOMParser();
            parser.setFeature("http://xml.org/sax/features/validation", false);
            parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
            parser.setFeature("http://apache.org/xml/features/dom/defer-node-expansion", false);
            if(resolver != null)
            {
                parser.setEntityResolver(this.resolver);
            }
            parser.setErrorHandler(new ParseErrorHandler());
            parser.parse(xml_source);
            
            Document doc = parser.getDocument();
            return doc;

        }
        catch (Exception e)
        {
            logger.error(e.getMessage(), e);

        }
        return null;
    }

    /** returns a DOM document */
    public Document getDOM(File in, String encoding)
    {
        try
        {

            InputStreamReader isr = new InputStreamReader(new FileInputStream(in), encoding);
            InputSource xml_source = new InputSource(isr);

            DOMParser parser = new DOMParser();
            parser.setFeature("http://xml.org/sax/features/validation", false);
            parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
            parser.setFeature("http://apache.org/xml/features/dom/defer-node-expansion", false);
            if(resolver != null)
            {
                parser.setEntityResolver(this.resolver);
            }
            parser.setErrorHandler(new ParseErrorHandler());
            parser.parse(xml_source);
            
            Document doc = parser.getDocument();

            return doc;

        }
        catch (Exception e)
        {
            logger.error(e.getMessage());
        }
        return null;
    }

    /** creates a new empty DOM Document */
    public static Document newDOM()
    {
        Document doc = new DocumentImpl();
        return doc;
    }

    /**
     * This method's parameters represent the parts of the Doctype of this
     * Document that is to be created. For more info see
     * http://xerces.apache.org
     * /xerces-j/apiDocs/org/apache/xerces/dom/DocumentTypeImpl
     * .html#DocumentTypeImpl
     * (org.apache.xerces.dom.CoreDocumentImpl,%20java.lang.String)
     * 
     * */
    public static Document newDOM(String qualifiedName, String publicID, String systemID)
    {
        // create empty DOM document
        DocumentImpl docImpl = new DocumentImpl();

        // Need to use the document to create the docType for it
        DocumentType myDocType = new DocumentTypeImpl(docImpl, qualifiedName, publicID, systemID);

        // Although we have created the docType using the document, we need to still 
        // put it into the empty document we just created 
        try
        {
            docImpl.appendChild(myDocType);
        }
        catch (Exception e)
        {
            System.out.println("Could not append docType because: " + e);
        }

        // return the document containing a DocType
        return docImpl;
    }

    /** returns the Node as a String */
    public static String getString(Node xmlNode)
    {
        outputEscaping = true;
        StringBuffer xmlRepresentation = new StringBuffer();
        getString(xmlNode, xmlRepresentation, 0, false);
        return xmlRepresentation.toString();
    }

    /**
     * returns the node as a nicely formatted String - this introduces extra
     * text nodes if the String is read back in as a DOM, so should only be used
     * for printing
     */
    public static String getPrettyString(Node xmlNode)
    {

        outputEscaping = true;
        StringBuffer xmlRepresentation = new StringBuffer();
        getString(xmlNode, xmlRepresentation, 0, true);
        return xmlRepresentation.toString();
    }

    /*
     * For the purposes of logger.debug statements, where this is called and
     * hence outputted, returns an empty string if debugging is not enabled
     */
    public static String getPrettyStringLogger(Node xmlNode, Logger log)
    {

        if (log.isDebugEnabled())
            return getPrettyString(xmlNode);

        return "";

    }

    private static void getString(Node xmlNode, StringBuffer xmlRepresentation, int depth, boolean pretty)
    {

        if (xmlNode == null)
        {
            xmlRepresentation.append("<null>");
            return;
        }

        short nodeType = xmlNode.getNodeType();
        String nodeName = xmlNode.getNodeName();

        if (nodeType == Node.DOCUMENT_NODE)
        {
            Document xmlDocNode = (Document) xmlNode;

            //if (xmlDocNode.getDoctype() == null) {
            //System.err.println("Doctype is null.");
            //}
            //else {
            if (xmlDocNode.getDoctype() != null)
            {
                DocumentType dt = xmlDocNode.getDoctype();

                String name = dt.getName();
                String pid = dt.getPublicId();
                String sid = dt.getSystemId();

                // Use previously assigned name, not dt.getName() again
                String doctype_str = "<!DOCTYPE " + name + " PUBLIC \"" + pid + "\" \"" + sid + "\">\n";

                xmlRepresentation.append(doctype_str);
            }
            getString(xmlDocNode.getDocumentElement(), xmlRepresentation, depth, pretty);
            return;
        }
        // Handle Element nodes
        if (nodeType == Node.ELEMENT_NODE)
        {
            if (pretty)
            {
                xmlRepresentation.append("\n");
                for (int i = 0; i < depth; i++)
                {
                    xmlRepresentation.append("  ");
                }
            }

            // Write opening tag
            xmlRepresentation.append("<");
            xmlRepresentation.append(nodeName);

            // Write the node attributes
            NamedNodeMap nodeAttributes = xmlNode.getAttributes();
            for (int i = 0; i < nodeAttributes.getLength(); i++)
            {
                Node attribute = nodeAttributes.item(i);
                xmlRepresentation.append(" ");
                xmlRepresentation.append(attribute.getNodeName());
                xmlRepresentation.append("=\"");
                xmlRepresentation.append(attribute.getNodeValue());
                xmlRepresentation.append("\"");
            }

            // If the node has no children, close the opening tag and return
            if (xmlNode.hasChildNodes() == false)
            {
                // This produces somewhat ugly output, but it is necessary to compensate
                // for display bugs in Netscape. Firstly, the space is needed before the
                // closing bracket otherwise Netscape will ignore some tags (<br/>, for
                // example). Also, a newline character would be expected after the tag,
                // but this causes problems with the display of links (the link text
                // will contain a newline character, which is displayed badly).
                xmlRepresentation.append(" />");
                return;
            }

            // Close the opening tag
            xmlRepresentation.append(">");

            // Apply recursively to the children of this node
            // hack for nodes next to text nodes - dont make them pretty
            // this is needed for text inside a <pre> element - any new lines 
            // or spaces around the span elements show up in the text
            NodeList children = xmlNode.getChildNodes();
            boolean do_pretty = pretty;
            for (int i = 0; i < children.getLength(); i++)
            {
                if (children.item(i).getNodeType() == Node.TEXT_NODE)
                {
                    do_pretty = false; // if there is a text node amongst the children, do teh following nodes in non-pretty mode - hope this doesn't stuff up something else
                }
                getString(children.item(i), xmlRepresentation, depth + 1, do_pretty);
            }

            // Write closing tag
            if (pretty)
            {
                if (xmlRepresentation.charAt(xmlRepresentation.length() - 1) == '\n')
                {
                    for (int i = 0; i < depth; i++)
                        xmlRepresentation.append("  ");
                }
            }
            xmlRepresentation.append("</");
            xmlRepresentation.append(nodeName);
            xmlRepresentation.append(">");
            if (pretty)
            {
                xmlRepresentation.append("\n");
            }
        }

        // Handle Text nodes
        else if (nodeType == Node.TEXT_NODE)
        {
            String text = xmlNode.getNodeValue();

            // Perform output escaping, if required
            // Apache Commons replace method is far superior to String.replaceAll - very fast!
            if (outputEscaping)
            {

                text = StringUtils.replace(text, "&", "&amp;");
                text = StringUtils.replace(text, "<", "&lt;");
                text = StringUtils.replace(text, ">", "&gt;");
                text = StringUtils.replace(text, "'", "&apos;");
                text = StringUtils.replace(text, "\"", "&quot;");
            }

            // Remove any control-C characters
            text = StringUtils.replace(text, "" + (char) 3, "");

            xmlRepresentation.append(text);
        }

        // Handle Processing Instruction nodes
        else if (nodeType == Node.PROCESSING_INSTRUCTION_NODE)
        {
            if (nodeName.equals("javax.xml.transform.disable-output-escaping"))
            {
                outputEscaping = false;
            }
            else if (nodeName.equals("javax.xml.transform.enable-output-escaping"))
            {
                outputEscaping = true;
            }
            else
            {
                logger.warn("Unhandled processing instruction " + nodeName);
            }
        }

        else if (nodeType == Node.COMMENT_NODE)
        {
            String text = xmlNode.getNodeValue();
            xmlRepresentation.append("<!-- ");
            xmlRepresentation.append(text);
            xmlRepresentation.append(" -->");
        }

        // A type of node that is not handled yet
        else
        {
            logger.warn("Unknown node type: " + nodeType + " " + getNodeTypeString(nodeType));
        }

        return;
    }

    protected static String getNodeTypeString(short node_type)
    {

        String type = "";
        switch (node_type)
        {
        case Node.ATTRIBUTE_NODE:
            type = "ATTRIBUTE_NODE";
            break;
        case Node.CDATA_SECTION_NODE:
            type = "CDATA_SECTION_NODE";
            break;
        case Node.COMMENT_NODE:
            type = "COMMENT_NODE";
            break;
        case Node.DOCUMENT_FRAGMENT_NODE:
            type = "DOCUMENT_FRAGMENT_NODE";
            break;
        case Node.DOCUMENT_NODE:
            type = "DOCUMENT_NODE";
            break;
        case Node.DOCUMENT_TYPE_NODE:
            type = "DOCUMENT_TYPE_NODE";
            break;
        case Node.ELEMENT_NODE:
            type = "ELEMENT_NODE";
            break;
        case Node.ENTITY_NODE:
            type = "ENTITY_NODE";
            break;
        case Node.ENTITY_REFERENCE_NODE:
            type = "ENTITY_REFERENCE_NODE";
            break;
        case Node.NOTATION_NODE:
            type = "NOTATION_NODE";
            break;
        case Node.PROCESSING_INSTRUCTION_NODE:
            type = "PROCESSING_INSTRUCTION_NODE";
            break;
        case Node.TEXT_NODE:
            type = "TEXT_NODE";
            break;
        default:
            type = "UNKNOWN";
        }

        return type;
    }

    // returns null if there no error occurred during parsing, or else returns the error message
    public String getParseErrorMessage()
    {
        ParseErrorHandler errorHandler = (ParseErrorHandler) this.parser.getErrorHandler();
        return errorHandler.getErrorMessage();
    }

    // Errorhandler for SAXParseExceptions that are errors, fatal errors or warnings. This class can be used to 
    // register a handler for any fatal errors, errors and warnings that may occur when parsing an xml file. 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 ParseErrorHandler implements ErrorHandler
    {
        protected String errorMessage = null;

        //  Receive notification of a recoverable error.
        public void error(SAXParseException exception)
        {
            handleError("Error:\n", exception);
        }

        //   Receive notification of a non-recoverable error.
        public void fatalError(SAXParseException exception)
        {
            handleError("Fatal Error:\n", exception);
        }

        // Receive notification of a warning.
        public void warning(SAXParseException exception)
        {
            handleError("Warning:\n", exception);
        }

        public String toString(SAXParseException e)
        {
            String msg = e.getMessage();
            msg += "\nOn line(column): " + e.getLineNumber() + "(" + e.getColumnNumber() + ")";
            msg += (e.getPublicId() != null) ? ("\npublic ID: " + e.getPublicId()) : "\nNo public ID";
            msg += (e.getSystemId() != null) ? ("\nsystem ID: " + e.getSystemId()) : "\nNo system ID";

            return msg;
        }

        // 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, SAXParseException exception)
        {
            this.errorMessage = errorType + toString(exception);
            System.err.println("\n****Error parsing xml:\n" + this.errorMessage + "\n****\n");
            logger.error(this.errorMessage);
        }
    }
}