1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache license, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the license for the specific language governing permissions and 15 * limitations under the license. 16 */ 17 package org.apache.logging.log4j.core; 18 19 import java.io.Serializable; 20 import java.util.Map; 21 22 /** 23 * Lays out a {@linkplain LogEvent} in different formats. 24 * 25 * The formats are: 26 * <ul> 27 * <li> 28 * {@code byte[]}</li> 29 * <li> 30 * an implementer of {@linkplain Serializable}, like {@code byte[]}</li> 31 * <li> 32 * {@linkplain String}</li> 33 * <li> 34 * {@linkplain LogEvent}</li> 35 * </ul> 36 * 37 * @param <T> 38 * The {@link Serializable} type returned by {@link #toSerializable(LogEvent)} 39 * 40 * @doubt There is still a need for a character-based layout for character based event sinks (databases, etc). Would 41 * introduce an EventEncoder, EventRenderer or something similar for the logging event to byte encoding. (RG) A layout 42 * can be configured with a Charset and then Strings can be converted to byte arrays. OTOH, it isn't possible to write 43 * byte arrays as character streams. 44 */ 45 public interface Layout<T extends Serializable> { 46 /** 47 * Returns the format for the layout format. 48 * @return The footer. 49 * @doubt the concept of header and footer is not universal, should not be on the base interface. 50 * (RG) I agree with this. 51 */ 52 byte[] getFooter(); 53 54 /** 55 * Returns the header for the layout format. 56 * @return The header. 57 * @doubt the concept of header and footer is not universal, should not be on the base interface. 58 * (RG) I agree with this. 59 */ 60 byte[] getHeader(); 61 62 /** 63 * Formats the event suitable for display. 64 * 65 * @param event The Logging Event. 66 * @return The formatted event. 67 * @doubt Likely better to write to a OutputStream instead of return a byte[]. (RG) That limits how the 68 * Appender can use the Layout. For example, it might concatenate information in front or behind the 69 * data and then write it all to the OutputStream in one call. 70 */ 71 byte[] toByteArray(LogEvent event); 72 73 /** 74 * Formats the event as an Object that can be serialized. 75 * 76 * @param event The Logging Event. 77 * @return The formatted event. 78 */ 79 T toSerializable(LogEvent event); 80 81 /** 82 * Returns the content type output by this layout. The base class returns "text/plain". 83 * 84 * @return the content type. 85 */ 86 String getContentType(); 87 88 /** 89 * Returns a description of the content format. 90 * 91 * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content format descriptors are specified. 92 * 93 */ 94 Map<String, String> getContentFormat(); 95 }