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 java.io.ByteArrayInputStream;
021import java.io.InputStream;
022
023import org.apache.logging.log4j.Logger;
024import org.apache.logging.log4j.status.StatusLogger;
025import org.apache.logging.log4j.util.Constants;
026import org.xml.sax.EntityResolver;
027import org.xml.sax.InputSource;
028
029/**
030 * An {@link EntityResolver} specifically designed to return
031 * <code>log4j.dtd</code> which is embedded within the log4j jar
032 * file.
033 */
034public class Log4jEntityResolver implements EntityResolver {
035    private static final Logger LOGGER = StatusLogger.getLogger();
036    private static final String PUBLIC_ID = "-//APACHE//DTD LOG4J 1.2//EN";
037
038    @Override
039    public InputSource resolveEntity(String publicId, String systemId) {
040        if (systemId.endsWith("log4j.dtd") || PUBLIC_ID.equals(publicId)) {
041            Class<?> clazz = getClass();
042            InputStream in = clazz.getResourceAsStream("/org/apache/log4j/xml/log4j.dtd");
043            if (in == null) {
044                LOGGER.warn("Could not find [log4j.dtd] using [{}] class loader, parsed without DTD.",
045                        clazz.getClassLoader());
046                in = new ByteArrayInputStream(Constants.EMPTY_BYTE_ARRAY);
047            }
048            return new InputSource(in);
049        }
050        return null;
051    }
052}