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 * TODO 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 /**
48 * Main plugin element type for Layout plugins.
49 *
50 * @since 2.1
51 */
52 String ELEMENT_TYPE = "layout";
53
54 /**
55 * Returns the format for the layout format.
56 * @return The footer.
57 */
58 byte[] getFooter();
59
60 /**
61 * Returns the header for the layout format.
62 * @return The header.
63 */
64 byte[] getHeader();
65
66 /**
67 * Formats the event suitable for display.
68 *
69 * @param event The Logging Event.
70 * @return The formatted event.
71 * TODO Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
72 * Appender can use the Layout. For example, it might concatenate information in front or behind the
73 * data and then write it all to the OutputStream in one call.
74 */
75 byte[] toByteArray(LogEvent event);
76
77 // TODO: it would be nice to provide ByteBuffers alongside the byte[]s
78
79 /**
80 * Formats the event as an Object that can be serialized.
81 *
82 * @param event The Logging Event.
83 * @return The formatted event.
84 */
85 T toSerializable(LogEvent event);
86
87 /**
88 * Returns the content type output by this layout. The base class returns "text/plain".
89 *
90 * @return the content type.
91 */
92 String getContentType();
93
94 /**
95 * Returns a description of the content format.
96 *
97 * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content
98 * format descriptors are specified.
99 */
100 Map<String, String> getContentFormat();
101 }