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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.core.pattern;
15  
16  /**
17   * A minimal converter which sets up the general interface for derived classes. 
18   * It also implements the functionality to chain converters in a linked list.
19   * 
20   * @author ceki
21   */
22  abstract public class Converter<E> {
23  
24      Converter<E> next;
25  
26      /**
27       * The convert method is responsible for extracting data from the event and
28       * storing it for later use by the write method.
29       * 
30       * @param event
31       */
32      public abstract String convert(E event);
33  
34      /**
35       * In its simplest incarnation, a convert simply appends the data extracted from
36       * the event to the buffer passed as parameter.
37       * 
38       * @param buf The input buffer where data is appended
39       * @param event The event from where data is extracted
40       */
41      public void write(StringBuilder buf, E event) {
42          buf.append(convert(event));
43      }
44  
45      public final void setNext(Converter<E> next) {
46          if (this.next != null) {
47              throw new IllegalStateException("Next converter has been already set");
48          }
49          this.next = next;
50      }
51  
52      public final Converter<E> getNext() {
53          return next;
54      }
55  }