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.message;
18
19 import java.io.Serializable;
20 import org.apache.logging.log4j.util.StringBuilderFormattable;
21
22 /**
23 * An interface for various Message implementations that can be logged. Messages can act as wrappers
24 * around Objects so that user can have control over converting Objects to Strings when necessary without
25 * requiring complicated formatters and as a way to manipulate the message based on information available
26 * at runtime such as the locale of the system.
27 * <p>
28 * Custom Message implementations should consider implementing the {@link StringBuilderFormattable}
29 * interface for more efficient processing. Garbage-free Layouts will call
30 * {@link StringBuilderFormattable#formatTo(StringBuilder) formatTo(StringBuilder)} instead of
31 * {@link Message#getFormattedMessage()} if the Message implements StringBuilderFormattable.
32 * </p>
33 * <p>
34 * Note: Message objects should not be considered to be thread safe nor should they be assumed to be
35 * safely reusable even on the same thread. The logging system may provide information to the Message
36 * objects and the Messages might be queued for asynchronous delivery. Thus, any modifications to a
37 * Message object by an application should by avoided after the Message has been passed as a parameter on
38 * a Logger method.
39 * </p>
40 *
41 * @see StringBuilderFormattable
42 */
43 /*
44 * Implementation note: this interface extends Serializable since LogEvents must be serializable.
45 */
46 public interface Message extends Serializable {
47
48 /**
49 * Gets the Message formatted as a String. Each Message implementation determines the
50 * appropriate way to format the data encapsulated in the Message. Messages that provide
51 * more than one way of formatting the Message will implement MultiformatMessage.
52 * <p>
53 * When configured to log asynchronously, this method is called before the Message is queued, unless this
54 * message implements {@link ReusableMessage} or is annotated with {@link AsynchronouslyFormattable}.
55 * This gives the Message implementation class a chance to create a formatted message String with the current value
56 * of any mutable objects.
57 * The intention is that the Message implementation caches this formatted message and returns it on subsequent
58 * calls. (See <a href="https://issues.apache.org/jira/browse/LOG4J2-763">LOG4J2-763</a>.)
59 * </p>
60 * <p>
61 * When logging synchronously, this method will not be called for Messages that implement the
62 * {@link StringBuilderFormattable} interface: instead, the
63 * {@link StringBuilderFormattable#formatTo(StringBuilder) formatTo(StringBuilder)} method will be called so the
64 * Message can format its contents without creating intermediate String objects.
65 * </p>
66 *
67 * @return The message String.
68 */
69 String getFormattedMessage();
70
71 /**
72 * Gets the format portion of the Message.
73 *
74 * @return The message format. Some implementations, such as ParameterizedMessage, will use this as
75 * the message "pattern". Other Messages may simply return an empty String.
76 * TODO Do all messages have a format? What syntax? Using a Formatter object could be cleaner.
77 * (RG) In SimpleMessage the format is identical to the formatted message. In ParameterizedMessage and
78 * StructuredDataMessage it is not. It is up to the Message implementer to determine what this
79 * method will return. A Formatter is inappropriate as this is very specific to the Message
80 * implementation so it isn't clear to me how having a Formatter separate from the Message would be cleaner.
81 */
82 String getFormat();
83
84 /**
85 * Gets parameter values, if any.
86 *
87 * @return An array of parameter values or null.
88 */
89 Object[] getParameters();
90
91 /**
92 * Gets the throwable, if any.
93 *
94 * @return the throwable or null.
95 */
96 Throwable getThrowable();
97 }