001/*-------------------------------------------------------------------------+
002|                                                                          |
003| Copyright 2005-2011 the ConQAT Project                                   |
004|                                                                          |
005| Licensed under the Apache License, Version 2.0 (the "License");          |
006| you may not use this file except in compliance with the License.         |
007| You may obtain a copy of the License at                                  |
008|                                                                          |
009|    http://www.apache.org/licenses/LICENSE-2.0                            |
010|                                                                          |
011| Unless required by applicable law or agreed to in writing, software      |
012| distributed under the License is distributed on an "AS IS" BASIS,        |
013| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
014| See the License for the specific language governing permissions and      |
015| limitations under the License.                                           |
016+-------------------------------------------------------------------------*/
017package org.conqat.lib.commons.xml;
018
019import java.io.ByteArrayInputStream;
020import java.io.IOException;
021
022import org.xml.sax.InputSource;
023import org.xml.sax.SAXException;
024import org.xml.sax.helpers.DefaultHandler;
025
026/**
027 * Base class for SAX parser handlers. This class has a default implementation
028 * of {@link #resolveEntity(String, String)} that works around a bug in the Java
029 * SAX parser implementation:
030 * 
031 * If {@link #resolveEntity(String, String)} returns <code>null</code> for a
032 * given DTD (the default behavior of {@link DefaultHandler}), the Java SAX
033 * parser will try to download that DTD. This will fail on machines that have no
034 * Internet connection or require a proxy to access the Internet or for DTDs
035 * where the URI is not a valid URL. This class' default implementation instead
036 * returns an empty {@link InputSource}, which effectively causes the parser to
037 * skip DTD validation.
038 * 
039 * Please note that downloading the DTD from the Internet is against the DTD
040 * specification (as the DTD URI is not required to be a valid URL) and is
041 * highly error-prone, resulting in a hard to interpret error message. It is
042 * thus recommended you use this base class and never return <code>null</code>
043 * from {@link #resolveEntity(String, String)}.
044 */
045public class OfflineSaxHandlerBase extends DefaultHandler {
046
047        /**
048         * {@inheritDoc}
049         * 
050         * Default implementation that can be overwritten by subclasses. This
051         * implementation returns an empty document for any entity that should be
052         * resolved. This effectively causes the parser to skip DTD validation.
053         * 
054         * @throws IOException
055         *             may be thrown by subclasses.
056         * @throws SAXException
057         *             may be thrown by subclasses.
058         */
059        @Override
060        public InputSource resolveEntity(String publicId, String systemId) throws IOException, SAXException {
061                return new InputSource(new ByteArrayInputStream(new byte[0]));
062        }
063
064}