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 }