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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.pattern;
19  
20  import org.apache.log4j.spi.LoggingEvent;
21  
22  
23  /**
24   * LoggingEventPatternConverter is a base class for pattern converters
25   * that can format information from instances of LoggingEvent.
26   *
27   * @author Curt Arnold
28   *
29   */
30  public abstract class LoggingEventPatternConverter extends PatternConverter {
31    /**
32     * Constructs an instance of LoggingEventPatternConverter.
33     * @param name name of converter.
34     * @param style CSS style for output.
35     */
36    protected LoggingEventPatternConverter(
37      final String name, final String style) {
38      super(name, style);
39    }
40  
41    /**
42     * Formats an event into a string buffer.
43     * @param event event to format, may not be null.
44     * @param toAppendTo string buffer to which the formatted event will be appended.  May not be null.
45     */
46    public abstract void format(
47      final LoggingEvent event, final StringBuffer toAppendTo);
48  
49    /**
50     * {@inheritDoc}
51     */
52    public void format(final Object obj, final StringBuffer output) {
53      if (obj instanceof LoggingEvent) {
54        format((LoggingEvent) obj, output);
55      }
56    }
57  
58    /**
59     * Normally pattern converters are not meant to handle Exceptions although
60     * few pattern converters might.
61     *
62     * By examining the return values for this method, the containing layout will
63     * determine whether it handles throwables or not.
64  
65     * @return true if this PatternConverter handles throwables
66     */
67    public boolean handlesThrowable() {
68      return false;
69    }
70  }