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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  package org.apache.log4j.spi;
18  
19  import org.apache.log4j.Appender;
20  import org.apache.log4j.Logger;
21  
22  
23  /**
24   * Appenders may delegate their error handling to
25   * <code>ErrorHandlers</code>.
26   * <p/>
27   * <p>Error handling is a particularly tedious to get right because by
28   * definition errors are hard to predict and to reproduce.
29   * <p/>
30   * <p/>
31   * <p>Please take the time to contact the author in case you discover
32   * that errors are not properly handled. You are most welcome to
33   * suggest new error handling policies or criticize existing policies.
34   */
35  public interface ErrorHandler {
36  
37      /**
38       * Add a reference to a logger to which the failing appender might
39       * be attached to. The failing appender will be searched and
40       * replaced only in the loggers you add through this method.
41       *
42       * @param logger One of the loggers that will be searched for the failing
43       *               appender in view of replacement.
44       * @since 1.2
45       */
46      void setLogger(Logger logger);
47  
48  
49      /**
50       * Equivalent to the {@link #error(String, Exception, int,
51       * LoggingEvent)} with the the event parameter set to
52       * <code>null</code>.
53       *
54       * @param message   The message associated with the error.
55       * @param e         The Exception that was thrown when the error occurred.
56       * @param errorCode The error code associated with the error.
57       */
58      void error(String message, Exception e, int errorCode);
59  
60      /**
61       * This method is normally used to just print the error message
62       * passed as a parameter.
63       *
64       * @param message   The message associated with the error.
65       */
66      void error(String message);
67  
68      /**
69       * This method is invoked to handle the error.
70       *
71       * @param message   The message associated with the error.
72       * @param e         The Exception that was thrown when the error occurred.
73       * @param errorCode The error code associated with the error.
74       * @param event     The logging event that the failing appender is asked
75       *                  to log.
76       * @since 1.2
77       */
78      void error(String message, Exception e, int errorCode, LoggingEvent event);
79  
80      /**
81       * Set the appender for which errors are handled. This method is
82       * usually called when the error handler is configured.
83       *
84       * @param appender The appender
85       * @since 1.2
86       */
87      void setAppender(Appender appender);
88  
89      /**
90       * Set the appender to fallback upon in case of failure.
91       *
92       * @param appender The backup appender
93       * @since 1.2
94       */
95      void setBackupAppender(Appender appender);
96  }
97