tapestry/tapestry-framework/src/java/org/apache/tapestry/util/xml/RuleDirectedParser.java

// Copyright 2004, 2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package org.apache.tapestry.util.xml;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hivemind.ApplicationRuntimeException;
import org.apache.hivemind.HiveMind;
import org.apache.hivemind.Location;
import org.apache.hivemind.Resource;
import org.apache.hivemind.impl.LocationImpl;
import org.apache.tapestry.Tapestry;
import org.apache.tapestry.util.RegexpMatcher;
import org.xml.sax.*;
import org.xml.sax.helpers.DefaultHandler;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * A simplified version of org.apache.commons.digester.Digester. This version is without as
 * many bells and whistles but has some key features needed when parsing a document (rather than a
 * configuration file): <br>
 * <ul>
 * <li>Notifications for each bit of text</li>
 * <li>Tracking of exact location within the document.</li>
 * </ul>
 * <p>
 * Like Digester, there's an object stack and a rule stack. The rules are much simpler (more
 * coding), in that there's a one-to-one relationship between an element and a rule.
 * <p>
 * Based on SAX2.
 *
 * @author Howard Lewis Ship
 * @since 3.0
 */

public class RuleDirectedParser extends DefaultHandler
{
    private static final Log LOG = LogFactory.getLog(RuleDirectedParser.class);

    private static SAXParserFactory _parserFactory;

    private Resource _documentLocation;

    private List _ruleStack = new ArrayList();

    private List _objectStack = new ArrayList();

    private Object _documentObject;

    private Locator _locator;

    private int _line = -1;

    private int _column = -1;

    private Location _location;

    private SAXParser _parser;

    private RegexpMatcher _matcher;

    private String _uri;

    private String _localName;

    private String _qName;

    /**
     * Map of {@link IRule}keyed on the local name of the element.
     */
    private Map _ruleMap = new HashMap();

    /**
     * Used to accumlate content provided by
     * {@link org.xml.sax.ContentHandler#characters(char[], int, int)}.
     */

    private StringBuffer _contentBuffer = new StringBuffer();

    /**
     * Map of paths to external entities (such as the DTD) keyed on public id.
     */

    private Map _entities = new HashMap();

    public Object parse(Resource documentLocation)
    {
        if (LOG.isDebugEnabled())
            LOG.debug("Parsing: " + documentLocation);

        try
        {
            _documentLocation = documentLocation;

            URL url = documentLocation.getResourceURL();

            if (url == null)
                throw new DocumentParseException(Tapestry.format("RuleDrivenParser.resource-missing", documentLocation), documentLocation);

            return parse(url);
        }
        finally
        {
            _documentLocation = null;
            _ruleStack.clear();
            _objectStack.clear();
            _documentObject = null;

            _uri = null;
            _localName = null;
            _qName = null;

            _line = -1;
            _column = -1;
            _location = null;
            _locator = null;

            _contentBuffer.setLength(0);
        }
    }

    protected Object parse(URL url)
    {
        if (_parser == null)
            _parser = constructParser();

        InputStream stream = null;

        try
        {
            stream = url.openStream();
        }
        catch (IOException ex)
        {
            throw new DocumentParseException(Tapestry.format(
              "RuleDrivenParser.unable-to-open-resource",
              url), _documentLocation, ex);
        }

        InputSource source = new InputSource(stream);

        try
        {
            _parser.parse(source, this);

            stream.close();
        }
        catch (Exception ex)
        {
            throw new DocumentParseException(Tapestry.format(
              "RuleDrivenParser.parse-error",
              url,
              ex.getMessage()), getLocation(), ex);
        }

        if (LOG.isDebugEnabled())
            LOG.debug("Document parsed as: " + _documentObject);

        return _documentObject;
    }

    /**
     * Returns an {@link Location}representing the current position within the document (depending
     * on the parser, this may be accurate to column number level).
     */

    public Location getLocation()
    {
        if (_locator == null)
            return null;

        int line = _locator.getLineNumber();
        int column = _locator.getColumnNumber();

        if (_line != line || _column != column)
        {
            _location = null;
            _line = line;
            _column = column;
        }

        if (_location == null)
            _location = new LocationImpl(_documentLocation, _line, _column);

        return _location;
    }

    /**
     * Pushes an object onto the object stack. The first object pushed is the "document object", the
     * root object returned by the parse.
     */
    public void push(Object object)
    {
        if (_documentObject == null)
            _documentObject = object;

        push(_objectStack, object, "object stack");
    }

    /**
     * Returns the top object on the object stack.
     */
    public Object peek()
    {
        return peek(_objectStack, 0);
    }

    /**
     * Returns an object within the object stack, at depth. Depth 0 is the top object, depth 1 is
     * the next-to-top object, etc.
     */

    public Object peek(int depth)
    {
        return peek(_objectStack, depth);
    }

    /**
     * Removes and returns the top object on the object stack.
     */
    public Object pop()
    {
        return pop(_objectStack, "object stack");
    }

    private Object pop(List list, String name)
    {
        Object result = list.remove(list.size() - 1);

        if (LOG.isDebugEnabled())
            LOG.debug("Popped " + result + " off " + name + " (at " + getLocation() + ")");

        return result;
    }

    private Object peek(List list, int depth)
    {
        return list.get(list.size() - 1 - depth);
    }

    private void push(List list, Object object, String name)
    {
        if (LOG.isDebugEnabled())
            LOG.debug("Pushing " + object + " onto " + name + " (at " + getLocation() + ")");

        list.add(object);
    }

    /**
     * Pushes a new rule onto the rule stack.
     */

    protected void pushRule(IRule rule)
    {
        push(_ruleStack, rule, "rule stack");
    }

    /**
     * Returns the top rule on the stack.
     */

    protected IRule peekRule()
    {
        return (IRule) peek(_ruleStack, 0);
    }

    protected IRule popRule()
    {
        return (IRule) pop(_ruleStack, "rule stack");
    }

    public void addRule(String localElementName, IRule rule)
    {
        _ruleMap.put(localElementName, rule);
    }

    /**
     * Registers a public id and corresponding input source. Generally, the source is a wrapper
     * around an input stream to a package resource.
     *
     * @param publicId
     *            the public identifier to be registerred, generally the publicId of a DTD related
     *            to the document being parsed
     * @param entityPath
     *            the resource path of the entity, typically a DTD file. Relative files names are
     *            expected to be stored in the same package as the class file, otherwise a leading
     *            slash is an absolute pathname within the classpath.
     */

    public void registerEntity(String publicId, String entityPath)
    {
        if (LOG.isDebugEnabled())
            LOG.debug("Registering " + publicId + " as " + entityPath);

        if (_entities == null)
            _entities = new HashMap();

        _entities.put(publicId, entityPath);
    }

    protected IRule selectRule(String localName, Attributes attributes)
    {
        IRule rule = (IRule) _ruleMap.get(localName);

        if (rule == null)
            throw new DocumentParseException(Tapestry.format(
              "RuleDrivenParser.no-rule-for-element",
              localName), getLocation());

        return rule;
    }

    /**
     * Uses the {@link Locator}to track the position in the document as a {@link Location}. This
     * is invoked once (before the initial element is parsed) and the Locator is retained and
     * queried as to the current file location.
     *
     * @see #getLocation()
     */
    public void setDocumentLocator(Locator locator)
    {
        _locator = locator;
    }

    /**
     * Accumulates the content in a buffer; the concatinated content is provided to the top rule
     * just before any start or end tag.
     */
    public void characters(char[] ch, int start, int length) throws SAXException
    {
        _contentBuffer.append(ch, start, length);
    }

    /**
     * Pops the top rule off the stack and invokes {@link IRule#endElement(RuleDirectedParser)}.
     */
    public void endElement(String uri, String localName, String qName) throws SAXException
    {
        fireContentRule();

        _uri = uri;
        _localName = localName;
        _qName = qName;

        popRule().endElement(this);
    }

    /**
     * Ignorable content is ignored.
     */
    public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException
    {
    }

    /**
     * Invokes {@link #selectRule(String, Attributes)}to choose a new rule, which is pushed onto
     * the rule stack, then invokes {@link IRule#startElement(RuleDirectedParser, Attributes)}.
     */
    public void startElement(String uri, String localName, String qName, Attributes attributes)
      throws SAXException
    {
        fireContentRule();

        _uri = uri;
        _localName = localName;
        _qName = qName;

        String name = extractName(uri, localName, qName);

        IRule newRule = selectRule(name, attributes);

        pushRule(newRule);

        newRule.startElement(this, attributes);
    }

    private String extractName(String uri, String localName, String qName)
    {
        return HiveMind.isBlank(localName) ? qName : localName;
    }

    /**
     * Uses {@link javax.xml.parsers.SAXParserFactory}to create a instance of a validation SAX2
     * parser.
     */
    protected synchronized SAXParser constructParser()
    {
        if (_parserFactory == null)
        {
            _parserFactory = SAXParserFactory.newInstance();
            configureParserFactory(_parserFactory);
        }

        try
        {
            return _parserFactory.newSAXParser();
        }
        catch (SAXException ex)
        {
            throw new ApplicationRuntimeException(ex);
        }
        catch (ParserConfigurationException ex)
        {
            throw new ApplicationRuntimeException(ex);
        }

    }

    /**
     * Configures a {@link SAXParserFactory}before {@link SAXParserFactory#newSAXParser()}is
     * invoked. The default implementation sets validating to true and namespaceAware to false,
     */

    protected void configureParserFactory(SAXParserFactory factory)
    {
        factory.setValidating(true);
        factory.setNamespaceAware(false);
    }

    /**
     * Throws the exception.
     */
    public void error(SAXParseException ex) throws SAXException
    {
        fatalError(ex);
    }

    /**
     * Throws the exception.
     */
    public void fatalError(SAXParseException ex) throws SAXException
    {
        // Sometimes, a bad parse "corrupts" a parser so that it doesn't
        // work properly for future parses (of valid documents),
        // so discard it here.

        _parser = null;

        throw ex;
    }

    /**
     * Throws the exception.
     */
    public void warning(SAXParseException ex) throws SAXException
    {
        fatalError(ex);
    }

    public InputSource resolveEntity(String publicId, String systemId) throws SAXException
    {
        String entityPath = null;

        if (LOG.isDebugEnabled())
            LOG.debug("Attempting to resolve entity; publicId = " + publicId + " systemId = "
                      + systemId);

        if (_entities != null)
            entityPath = (String) _entities.get(publicId);

        if (entityPath == null)
        {
            if (LOG.isDebugEnabled())
                LOG.debug("Entity not found, using " + systemId);

            return null;
        }

        InputStream stream = getClass().getResourceAsStream(entityPath);

        InputSource result = new InputSource(stream);

        if (result != null && LOG.isDebugEnabled())
            LOG.debug("Resolved " + publicId + " as " + result + " (for " + entityPath + ")");

        return result;
    }

    /**
     * Validates that the input value matches against the specified Perl5 pattern. If valid, the
     * method simply returns. If not a match, then an error message is generated (using the errorKey
     * and the input value) and a {@link InvalidStringException}is thrown.
     */

    public void validate(String value, String pattern, String errorKey)
    {
        if (_matcher == null)
            _matcher = new RegexpMatcher();

        if (_matcher.matches(pattern, value))
            return;

        throw new InvalidStringException(Tapestry.format(errorKey, value), value, getLocation());
    }

    public Resource getDocumentLocation()
    {
        return _documentLocation;
    }

    /**
     * Returns the localName for the current element.
     *
     * @see org.xml.sax.ContentHandler#startElement(java.lang.String, java.lang.String,
     *      java.lang.String, org.xml.sax.Attributes)
     */
    public String getLocalName()
    {
        return _localName;
    }

    /**
     * Returns the qualified name for the current element.
     *
     * @see org.xml.sax.ContentHandler#startElement(java.lang.String, java.lang.String,
     *      java.lang.String, org.xml.sax.Attributes)
     */
    public String getQName()
    {
        return _qName;
    }

    /**
     * Returns the URI for the current element.
     *
     * @see org.xml.sax.ContentHandler#startElement(java.lang.String, java.lang.String,
     *      java.lang.String, org.xml.sax.Attributes)
     */
    public String getUri()
    {
        return _uri;
    }

    private void fireContentRule()
    {
        String content = _contentBuffer.toString();
        _contentBuffer.setLength(0);

        if (!_ruleStack.isEmpty())
            peekRule().content(this, content);
    }

}