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    import java.util.Map;
021    
022    /**
023     * Lays out a {@linkplain LogEvent} in different formats.
024     *
025     * The formats are:
026     * <ul>
027     * <li>
028     * {@code byte[]}</li>
029     * <li>
030     * an implementer of {@linkplain Serializable}, like {@code byte[]}</li>
031     * <li>
032     * {@linkplain String}</li>
033     * <li>
034     * {@linkplain LogEvent}</li>
035     * </ul>
036     *
037     * @param <T>
038     *            The {@link Serializable} type returned by {@link #toSerializable(LogEvent)}
039     *
040     * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would
041     * introduce an EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout
042     * can be configured with a Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write
043     * byte arrays as character streams.
044     */
045    public interface Layout<T extends Serializable> {
046        /**
047         * Returns the format for the layout format.
048         * @return The footer.
049         */
050        byte[] getFooter();
051    
052        /**
053         * Returns the header for the layout format.
054         * @return The header.
055         */
056        byte[] getHeader();
057    
058        /**
059         * Formats the event suitable for display.
060         *
061         * @param event The Logging Event.
062         * @return The formatted event.
063         * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
064         * Appender can use the Layout. For example, it might concatenate information in front or behind the
065         * data and then write it all to the OutputStream in one call.
066         */
067        byte[] toByteArray(LogEvent event);
068    
069        /**
070         * Formats the event as an Object that can be serialized.
071         *
072         * @param event The Logging Event.
073         * @return The formatted event.
074         */
075        T toSerializable(LogEvent event);
076    
077        /**
078         * Returns the content type output by this layout. The base class returns "text/plain".
079         *
080         * @return the content type.
081         */
082        String getContentType();
083    
084        /**
085         * Returns a description of the content format.
086         *
087         * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content format descriptors are specified.
088         *
089         */
090        Map<String, String> getContentFormat();
091    }