001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  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 */
017
018package org.apache.log4j.xml;
019
020import org.apache.log4j.helpers.LogLog;
021import org.xml.sax.EntityResolver;
022import org.xml.sax.InputSource;
023
024import java.io.InputStream;
025import java.io.ByteArrayInputStream;
026
027/**
028 * An {@link EntityResolver} specifically designed to return
029 * <code>log4j.dtd</code> which is embedded within the log4j jar
030 * file. 
031 *
032 * @author Paul Austin
033 * */
034public class Log4jEntityResolver implements EntityResolver {
035  private static final String PUBLIC_ID = "-//APACHE//DTD LOG4J 1.2//EN";
036
037  public InputSource resolveEntity (String publicId, String systemId) {
038    if (systemId.endsWith("log4j.dtd")  || PUBLIC_ID.equals(publicId)) {
039      Class clazz = getClass();
040      InputStream in = clazz.getResourceAsStream("/org/apache/log4j/xml/log4j.dtd");
041      if (in == null) {
042            LogLog.warn("Could not find [log4j.dtd] using [" + clazz.getClassLoader()
043                     + "] class loader, parsed without DTD.");
044        in = new ByteArrayInputStream(new byte[0]);
045      }
046          return new InputSource(in);
047    } else {
048      return null;
049    }
050  }
051}