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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.logging.log4j.core;
18  
19  import java.io.Serializable;
20  
21  /**
22   * Lays out a {@linkplain LogEvent} in different formats.
23   *
24   * The formats are:
25   * <ul>
26   * <li>
27   * {@code byte[]}</li>
28   * <li>
29   * an implementor of {@linkplain Serializable}, like {@code byte[]}</li>
30   * <li>
31   * {@linkplain String}</li>
32   * <li>
33   * {@linkplain LogEvent}</li>
34   * </ul>
35   *
36   * @param <T>
37   *            The {@link Serializable} type returned by {@link #toSerializable(LogEvent)}
38   *
39   * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would
40   * introduce an EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout
41   * can be configured with a Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write
42   * byte arrays as character streams.
43   */
44  public interface Layout<T extends Serializable> {
45      /**
46       * Returns the format for the layout format.
47       * @return The footer.
48       * @doubt the concept of header and footer is not universal, should not be on the base interface.
49       * (RG) I agree with this.
50       */
51      byte[] getFooter();
52  
53      /**
54       * Returns the header for the layout format.
55       * @return The header.
56       * @doubt the concept of header and footer is not universal, should not be on the base interface.
57       * (RG) I agree with this.
58       */
59      byte[] getHeader();
60  
61      /**
62       * Formats the event suitable for display.
63       *
64       * @param event The Logging Event.
65       * @return The formatted event.
66       * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
67       * Appender can use the Layout. For example, it might concatenate information in front or behind the
68       * data and then write it all to the OutputStream in one call.
69       */
70      byte[] toByteArray(LogEvent event);
71  
72      /**
73       * Formats the event as an Object that can be serialized.
74       *
75       * @param event The Logging Event.
76       * @return The formatted event.
77       */
78      T toSerializable(LogEvent event);
79  
80      /**
81       * Returns the content type output by this layout. The base class returns "text/plain".
82       *
83       * @return the content type.
84       */
85      String getContentType();
86  }