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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.log4j.xml;
19  
20  import org.apache.log4j.helpers.LogLog;
21  import org.xml.sax.EntityResolver;
22  import org.xml.sax.InputSource;
23  
24  import java.io.InputStream;
25  import java.io.ByteArrayInputStream;
26  
27  /**
28   * An {@link EntityResolver} specifically designed to return
29   * <code>log4j.dtd</code> which is embedded within the log4j jar
30   * file. 
31   *
32   * @author Paul Austin
33   * */
34  public class Log4jEntityResolver implements EntityResolver {
35    private static final String PUBLIC_ID = "-//APACHE//DTD LOG4J 1.2//EN";
36  
37    public InputSource resolveEntity (String publicId, String systemId) {
38      if (systemId.endsWith("log4j.dtd")  || PUBLIC_ID.equals(publicId)) {
39        Class clazz = getClass();
40        InputStream in = clazz.getResourceAsStream("/org/apache/log4j/xml/log4j.dtd");
41        if (in == null) {
42  	    LogLog.warn("Could not find [log4j.dtd] using [" + clazz.getClassLoader()
43  		     + "] class loader, parsed without DTD.");
44          in = new ByteArrayInputStream(new byte[0]);
45        }
46  	  return new InputSource(in);
47      } else {
48        return null;
49      }
50    }
51  }