1   /*
2    * Logback: the reliable, generic, fast and flexible logging framework.
3    * Copyright (C) 1999-2026, 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 v2.0 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   * @param <E> The type of the event object
21   * @author ceki
22   */
23  abstract public class Converter<E> {
24  
25      Converter<E> next;
26  
27      /**
28       * The convert method is responsible for extracting data from the event and
29       * storing it for later use by the write method.
30       * 
31       * @param event the event to convert
32       */
33      public abstract String convert(E event);
34  
35      /**
36       * In its simplest incarnation, a convert simply appends the data extracted from
37       * the event to the buffer passed as parameter.
38       * 
39       * @param buf   The input buffer where data is appended
40       * @param event The event from where data is extracted
41       */
42      public void write(StringBuilder buf, E event) {
43          buf.append(convert(event));
44      }
45  
46      public final void setNext(Converter<E> next) {
47          if (this.next != null) {
48              throw new IllegalStateException("Next converter has been already set");
49          }
50          this.next = next;
51      }
52  
53      public final Converter<E> getNext() {
54          return next;
55      }
56  }