    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     */
    017    package org.apache.logging.log4j.message;
    018
    019    import java.io.Serializable;
    020
    021    /**
    022     * An interface for various Message implementations that can be logged. Messages can act as wrappers
    023     * around Objects so that user can have control over converting Objects to Strings when necessary without
    024     * requiring complicated formatters and as a way to manipulate the message based on information available
    025     * at runtime such as the locale of the system.
    026     *<p>
    027     * Note: Message objects should not be considered to be thread safe nor should they be assumed to be
    028     * safely reusable even on the same thread. The logging system may provide information to the Message
    029     * objects and the Messages might be queued for asynchronous delivery. Thus, any modifications to a
    030     * Message object by an application should by avoided after the Message has been passed as a parameter on
    031     * a Logger method.
    032     * </p>
    033     * TODO Interfaces should rarely extend Serializable according to Effective Java 2nd Ed pg 291.
    034     * (RG) That section also says "If a class or interface exists primarily to participate in a framework that
    035     * requires all participants to implement Serializable, then it makes perfect sense for the class or
    036     * interface to implement or extend Serializable". Such is the case here as the LogEvent must be Serializable.
    037     */
    038    public interface Message extends Serializable {
    039
    040        /**
    041         * Gets the Message formatted as a String. Each Message implementation determines the
    042         * appropriate way to format the data encapsulated in the Message. Messages that provide
    043         * more than one way of formatting the Message will implement MultiformatMessage.
    044         *
    045         * @return The message String.
    046         */
    047        String getFormattedMessage();
    048
    049        /**
    050         * Gets the format portion of the Message.
    051         *
    052         * @return The message format. Some implementations, such as ParameterizedMessage, will use this as
    053         * the message "pattern". Other Messages may simply return an empty String.
    054         * TODO Do all messages have a format?  What syntax?  Using a Formatter object could be cleaner.
    055         * (RG) In SimpleMessage the format is identical to the formatted message. In ParameterizedMessage and
    056         * StructuredDataMessage it is not. It is up to the Message implementer to determine what this
    057         * method will return. A Formatter is inappropriate as this is very specific to the Message
    058         * implementation so it isn't clear to me how having a Formatter separate from the Message would be cleaner.
    059         */
    060        String getFormat();
    061
    062        /**
    063         * Gets parameter values, if any.
    064         *
    065         * @return An array of parameter values or null.
    066         */
    067        Object[] getParameters();
    068
    069        /**
    070         * Gets the throwable, if any.
    071         *
    072         * @return the throwable or null.
    073         */
    074        Throwable getThrowable();
    075    }