    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     * TODO 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        /**
    048         * Main plugin element type for Layout plugins.
    049         *
    050         * @since 2.1
    051         */
    052        String ELEMENT_TYPE = "layout";
    053
    054        /**
    055         * Returns the format for the layout format.
    056         * @return The footer.
    057         */
    058        byte[] getFooter();
    059
    060        /**
    061         * Returns the header for the layout format.
    062         * @return The header.
    063         */
    064        byte[] getHeader();
    065
    066        /**
    067         * Formats the event suitable for display.
    068         *
    069         * @param event The Logging Event.
    070         * @return The formatted event.
    071         * TODO Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the
    072         * Appender can use the Layout. For example, it might concatenate information in front or behind the
    073         * data and then write it all to the OutputStream in one call.
    074         */
    075        byte[] toByteArray(LogEvent event);
    076
    077        // TODO: it would be nice to provide ByteBuffers alongside the byte[]s
    078
    079        /**
    080         * Formats the event as an Object that can be serialized.
    081         *
    082         * @param event The Logging Event.
    083         * @return The formatted event.
    084         */
    085        T toSerializable(LogEvent event);
    086
    087        /**
    088         * Returns the content type output by this layout. The base class returns "text/plain".
    089         *
    090         * @return the content type.
    091         */
    092        String getContentType();
    093
    094        /**
    095         * Returns a description of the content format.
    096         *
    097         * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content
    098         * format descriptors are specified.
    099         */
    100        Map<String, String> getContentFormat();
    101    }