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.core;
018    
019    import java.io.Serializable;
020    
021    /**
022     * Lays out a {@linkplain LogEvent} in different formats. 
023     * The formats are: byte[], or an implementor of {@linkplain Serializable}, like {@code byte[]},
024     * String, and LogEvent.
025     * 
026     * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would introduce an
027     *        EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout can be configured with a
028     *        Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write byte arrays as character streams.
029     * @param <T>
030     *            The Object type that will be returned on the {@link #toSerializable(LogEvent)} call.
031     */
032    public interface Layout<T extends Serializable> {
033        /**
034         * Returns the format for the layout format.
035         * @return The footer.
036         * @doubt the concept of header and footer is not universal, should not be on the base interface.
037         * (RG) I agree with this.
038         */
039        byte[] getFooter();
040    
041        /**
042         * Returns the header for the layout format.
043         * @return The header.
044         * @doubt the concept of header and footer is not universal, should not be on the base interface.
045         * (RG) I agree with this.
046         */
047        byte[] getHeader();
048    
049        /**
050         * Formats the event suitable for display.
051         *
052         * @param event The Logging Event.
053         * @return The formatted event.
054         * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
055         * Appender can use the Layout. For example, it might concatenate information in front or behind the
056         * data and then write it all to the OutputStream in one call.
057         */
058        byte[] toByteArray(LogEvent event);
059    
060        /**
061         * Formats the event as an Object that can be serialized.
062         *
063         * @param event The Logging Event.
064         * @return The formatted event.
065         */
066        T toSerializable(LogEvent event);
067    
068    
069    }