PomHandler.java

/*******************************************************************************
 * Copyright (c) 2008-2010 Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *      Sonatype, Inc. - initial API and implementation
 *******************************************************************************/

package org.eclipse.m2e.core.internal.content;

import java.io.IOException;
import java.io.StringReader;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;


/**
 * An xml event handler for detecting the project top-level element in a POM file. Also records whether a default
 * attribute is present for the project and if any typical Maven elements are present.
 * 
 * @see org.eclipse.ant.internal.core.contentDescriber.AntHandler
 * @author Herve Boutemy
 * @since 0.9.6
 */
public final class PomHandler extends DefaultHandler {
  /**
   * An exception indicating that the parsing should stop.
   */
  private class StopParsingException extends SAXException {
    /**
     * All serializable objects should have a stable serialVersionUID
     */
    private static final long serialVersionUID = 1L;

    /**
     * Constructs an instance of <code>StopParsingException</code> with a <code>null</code> detail message.
     */
    public StopParsingException() {
      super((String) null);
    }
  }

  private static final String PROJECT = "project"; //$NON-NLS-1$

  private static final String ARTIFACTID = "artifactId"; //$NON-NLS-1$

  /**
   * This is the name of the top-level element found in the XML file. This member variable is <code>null</code> unless
   * the file has been parsed successful to the point of finding the top-level element.
   */
  private String fTopElementFound = null;

  private SAXParserFactory fFactory;

  private boolean fArtifactIdFound = false;

  private int fLevel = -1;

  /**
   * Creates a new SAX parser for use within this instance.
   * 
   * @return The newly created parser.
   * @throws ParserConfigurationException If a parser of the given configuration cannot be created.
   * @throws SAXException If something in general goes wrong when creating the parser.
   */
  private final SAXParser createParser(SAXParserFactory parserFactory) throws ParserConfigurationException,
      SAXException, SAXNotRecognizedException, SAXNotSupportedException {
    // Initialize the parser.
    final SAXParser parser = parserFactory.newSAXParser();
    final XMLReader reader = parser.getXMLReader();
    // disable DTD validation
    try {
      //  be sure validation is "off" or the feature to ignore DTD's will not apply
      reader.setFeature("http://xml.org/sax/features/validation", false); //$NON-NLS-1$
      reader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false); //$NON-NLS-1$
    } catch(SAXNotRecognizedException e) {
      // not a big deal if the parser does not recognize the features
    } catch(SAXNotSupportedException e) {
      // not a big deal if the parser does not support the features
    }
    return parser;
  }

  private SAXParserFactory getFactory() {
    synchronized(this) {
      if(fFactory != null) {
        return fFactory;
      }
      fFactory = SAXParserFactory.newInstance();
      fFactory.setNamespaceAware(true);
    }
    return fFactory;
  }

  protected boolean parseContents(InputSource contents) throws IOException, ParserConfigurationException, SAXException {
    // Parse the file into we have what we need (or an error occurs).
    try {
      fFactory = getFactory();
      if(fFactory == null) {
        return false;
      }
      final SAXParser parser = createParser(fFactory);
      // to support external entities specified as relative URIs (see bug 63298)
      contents.setSystemId("/"); //$NON-NLS-1$
      parser.parse(contents, this);
    } catch(StopParsingException e) {
      // Abort the parsing normally. Fall through...
    }
    return true;
  }

  /*
   * Resolve external entity definitions to an empty string.  This is to speed
   * up processing of files with external DTDs.  Not resolving the contents 
   * of the DTD is ok, as only the System ID of the DTD declaration is used.
   * @see org.xml.sax.helpers.DefaultHandler#resolveEntity(java.lang.String, java.lang.String)
   */
  @Override
  public InputSource resolveEntity(String publicId, String systemId) {
    return new InputSource(new StringReader("")); //$NON-NLS-1$
  }

  @Override
  public final void startElement(final String uri, final String elementName, final String qualifiedName,
      final Attributes attributes) throws SAXException {
    fLevel++ ;
    if(fTopElementFound == null) {
      fTopElementFound = elementName;
      if(!hasRootProjectElement()) {
        throw new StopParsingException();
      }
    }
    if(fLevel == 1 && ARTIFACTID.equals(elementName)) {
      fArtifactIdFound = true;
      throw new StopParsingException();
    }
  }

  @Override
  public void endElement(String uri, String localName, String qName) throws SAXException {
    super.endElement(uri, localName, qName);
    fLevel-- ;
  }

  protected boolean hasRootProjectElement() {
    return PROJECT.equals(fTopElementFound);
  }

  protected boolean hasArtifactIdElement() {
    return fArtifactIdFound;
  }
}