001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache license, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the license for the specific language governing permissions and
015 * limitations under the license.
016 */
017package org.apache.logging.log4j.message;
018
019import java.io.Serializable;
020import org.apache.logging.log4j.util.StringBuilderFormattable;
021
022/**
023 * An interface for various Message implementations that can be logged. Messages can act as wrappers
024 * around Objects so that user can have control over converting Objects to Strings when necessary without
025 * requiring complicated formatters and as a way to manipulate the message based on information available
026 * at runtime such as the locale of the system.
027 * <p>
028 * Custom Message implementations should consider implementing the {@link StringBuilderFormattable}
029 * interface for more efficient processing. Garbage-free Layouts will call
030 * {@link StringBuilderFormattable#formatTo(StringBuilder) formatTo(StringBuilder)} instead of
031 * {@link Message#getFormattedMessage()} if the Message implements StringBuilderFormattable.
032 * </p>
033 *<p>
034 * Note: Message objects should not be considered to be thread safe nor should they be assumed to be
035 * safely reusable even on the same thread. The logging system may provide information to the Message
036 * objects and the Messages might be queued for asynchronous delivery. Thus, any modifications to a
037 * Message object by an application should by avoided after the Message has been passed as a parameter on
038 * a Logger method.
039 * </p>
040 * TODO Interfaces should rarely extend Serializable according to Effective Java 2nd Ed pg 291.
041 * (RG) That section also says "If a class or interface exists primarily to participate in a framework that
042 * requires all participants to implement Serializable, then it makes perfect sense for the class or
043 * interface to implement or extend Serializable". Such is the case here as the LogEvent must be Serializable.
044 *
045 * @see StringBuilderFormattable
046 */
047public interface Message extends Serializable {
048
049    /**
050     * Gets the Message formatted as a String. Each Message implementation determines the
051     * appropriate way to format the data encapsulated in the Message. Messages that provide
052     * more than one way of formatting the Message will implement MultiformatMessage.
053     * <p>
054     * This method will not be called for Messages that implement the
055     * {@link StringBuilderFormattable} interface: instead, the
056     * {@link StringBuilderFormattable#formatTo(StringBuilder) formatTo(StringBuilder)} method will be called so the
057     * Message can format its contents without creating intermediate String objects.
058     * </p>
059     *
060     * @return The message String.
061     */
062    String getFormattedMessage();
063
064    /**
065     * Gets the format portion of the Message.
066     *
067     * @return The message format. Some implementations, such as ParameterizedMessage, will use this as
068     * the message "pattern". Other Messages may simply return an empty String.
069     * TODO Do all messages have a format?  What syntax?  Using a Formatter object could be cleaner.
070     * (RG) In SimpleMessage the format is identical to the formatted message. In ParameterizedMessage and
071     * StructuredDataMessage it is not. It is up to the Message implementer to determine what this
072     * method will return. A Formatter is inappropriate as this is very specific to the Message
073     * implementation so it isn't clear to me how having a Formatter separate from the Message would be cleaner.
074     */
075    String getFormat();
076
077    /**
078     * Gets parameter values, if any.
079     *
080     * @return An array of parameter values or null.
081     */
082    Object[] getParameters();
083
084    /**
085     * Gets the throwable, if any.
086     *
087     * @return the throwable or null.
088     */
089    Throwable getThrowable();
090}