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 * 024 * The formats are: 025 * <ul> 026 * <li> 027 * {@code byte[]}</li> 028 * <li> 029 * an implementor of {@linkplain Serializable}, like {@code byte[]}</li> 030 * <li> 031 * {@linkplain String}</li> 032 * <li> 033 * {@linkplain LogEvent}</li> 034 * </ul> 035 * 036 * @param <T> 037 * The {@link Serializable} type returned by {@link #toSerializable(LogEvent)} 038 * 039 * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would 040 * introduce an EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout 041 * can be configured with a Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write 042 * byte arrays as character streams. 043 */ 044 public interface Layout<T extends Serializable> { 045 /** 046 * Returns the format for the layout format. 047 * @return The footer. 048 * @doubt the concept of header and footer is not universal, should not be on the base interface. 049 * (RG) I agree with this. 050 */ 051 byte[] getFooter(); 052 053 /** 054 * Returns the header for the layout format. 055 * @return The header. 056 * @doubt the concept of header and footer is not universal, should not be on the base interface. 057 * (RG) I agree with this. 058 */ 059 byte[] getHeader(); 060 061 /** 062 * Formats the event suitable for display. 063 * 064 * @param event The Logging Event. 065 * @return The formatted event. 066 * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the 067 * Appender can use the Layout. For example, it might concatenate information in front or behind the 068 * data and then write it all to the OutputStream in one call. 069 */ 070 byte[] toByteArray(LogEvent event); 071 072 /** 073 * Formats the event as an Object that can be serialized. 074 * 075 * @param event The Logging Event. 076 * @return The formatted event. 077 */ 078 T toSerializable(LogEvent event); 079 080 /** 081 * Returns the content type output by this layout. The base class returns "text/plain". 082 * 083 * @return the content type. 084 */ 085 String getContentType(); 086 }