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 import java.util.Map;
21
22 /**
23 * Lays out a {@linkplain LogEvent} in different formats.
24 *
25 * The formats are:
26 * <ul>
27 * <li>
28 * {@code byte[]}</li>
29 * <li>
30 * an implementer of {@linkplain Serializable}, like {@code byte[]}</li>
31 * <li>
32 * {@linkplain String}</li>
33 * <li>
34 * {@linkplain LogEvent}</li>
35 * </ul>
36 *
37 * @param <T>
38 * The {@link Serializable} type returned by {@link #toSerializable(LogEvent)}
39 *
40 * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would
41 * introduce an EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout
42 * can be configured with a Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write
43 * byte arrays as character streams.
44 */
45 public interface Layout<T extends Serializable> {
46 /**
47 * Returns the format for the layout format.
48 * @return The footer.
49 */
50 byte[] getFooter();
51
52 /**
53 * Returns the header for the layout format.
54 * @return The header.
55 */
56 byte[] getHeader();
57
58 /**
59 * Formats the event suitable for display.
60 *
61 * @param event The Logging Event.
62 * @return The formatted event.
63 * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
64 * Appender can use the Layout. For example, it might concatenate information in front or behind the
65 * data and then write it all to the OutputStream in one call.
66 */
67 byte[] toByteArray(LogEvent event);
68
69 /**
70 * Formats the event as an Object that can be serialized.
71 *
72 * @param event The Logging Event.
73 * @return The formatted event.
74 */
75 T toSerializable(LogEvent event);
76
77 /**
78 * Returns the content type output by this layout. The base class returns "text/plain".
79 *
80 * @return the content type.
81 */
82 String getContentType();
83
84 /**
85 * Returns a description of the content format.
86 *
87 * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content format descriptors are specified.
88 *
89 */
90 Map<String, String> getContentFormat();
91 }