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1   /**
2    * Logback: the reliable, generic, fast and flexible logging framework.
3    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
4    *
5    * This program and the accompanying materials are dual-licensed under
6    * either the terms of the Eclipse Public License v1.0 as published by
7    * the Eclipse Foundation
8    *
9    *   or (per the licensee's choosing)
10   *
11   * under the terms of the GNU Lesser General Public License version 2.1
12   * as published by the Free Software Foundation.
13   */
14  package ch.qos.logback.classic.pattern;
15  
16  import ch.qos.logback.classic.LoggerContext;
17  import ch.qos.logback.classic.spi.ILoggingEvent;
18  import ch.qos.logback.core.Context;
19  import ch.qos.logback.core.pattern.Converter;
20  import ch.qos.logback.core.pattern.ConverterUtil;
21  import ch.qos.logback.core.pattern.PostCompileProcessor;
22  
23  public class EnsureExceptionHandling implements PostCompileProcessor<ILoggingEvent> {
24  
25      /**
26       * This implementation checks if any of the converters in the chain handles
27       * exceptions. If not, then this method adds a
28       * {@link ExtendedThrowableProxyConverter} instance to the end of the chain.
29       * <p>
30       * This allows appenders using this layout to output exception information
31       * event if the user forgets to add %ex to the pattern. Note that the
32       * appenders defined in the Core package are not aware of exceptions nor
33       * LoggingEvents.
34       * <p>
35       * If for some reason the user wishes to NOT print exceptions, then she can
36       * add %nopex to the pattern.
37       * 
38       * 
39       */
40      public void process(Context context, Converter<ILoggingEvent> head) {
41          if (head == null) {
42              // this should never happen
43              throw new IllegalArgumentException("cannot process empty chain");
44          }
45          if (!chainHandlesThrowable(head)) {
46              Converter<ILoggingEvent> tail = ConverterUtil.findTail(head);
47              Converter<ILoggingEvent> exConverter = null;
48              LoggerContext loggerContext = (LoggerContext) context;
49              if (loggerContext.isPackagingDataEnabled()) {
50                  exConverter = new ExtendedThrowableProxyConverter();
51              } else {
52                  exConverter = new ThrowableProxyConverter();
53              }
54              tail.setNext(exConverter);
55          }
56      }
57  
58      /**
59       * This method computes whether a chain of converters handles exceptions or
60       * not.
61       * 
62       * @param head
63       *                The first element of the chain
64       * @return true if can handle throwables contained in logging events
65       */
66      public boolean chainHandlesThrowable(Converter<ILoggingEvent> head) {
67          Converter<ILoggingEvent> c = head;
68          while (c != null) {
69              if (c instanceof ThrowableHandlingConverter) {
70                  return true;
71              }
72              c = c.getNext();
73          }
74          return false;
75      }
76  }