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.lookup;
018
019 import org.apache.logging.log4j.core.LogEvent;
020
021 /**
022 * Lookup a String key to a String value.
023 * <p>
024 * This class represents the simplest form of a string to string map.
025 * It has a benefit over a map in that it can create the result on
026 * demand based on the key.
027 * </p>
028 * <p>
029 * This class comes complete with various factory methods.
030 * If these do not suffice, you can subclass and implement your own matcher.
031 * </p>
032 * <p>
033 * For example, it would be possible to implement a lookup that used the
034 * key as a primary key, and looked up the value on demand from the database
035 * </p>
036 */
037 public interface StrLookup {
038
039 /**
040 * Main plugin category for StrLookup plugins.
041 *
042 * @since 2.1
043 */
044 String CATEGORY = "Lookup";
045
046 /**
047 * Looks up a String key to a String value.
048 * <p>
049 * The internal implementation may use any mechanism to return the value.
050 * The simplest implementation is to use a Map. However, virtually any
051 * implementation is possible.
052 * </p>
053 * <p>
054 * For example, it would be possible to implement a lookup that used the
055 * key as a primary key, and looked up the value on demand from the database
056 * Or, a numeric based implementation could be created that treats the key
057 * as an integer, increments the value and return the result as a string -
058 * converting 1 to 2, 15 to 16 etc.
059 * </p>
060 * <p>
061 * This method always returns a String, regardless of
062 * the underlying data, by converting it as necessary. For example:
063 * </p>
064 * <pre>
065 * Map<String, Object> map = new HashMap<String, Object>();
066 * map.put("number", new Integer(2));
067 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
068 * </pre>
069 * @param key the key to be looked up, may be null
070 * @return the matching value, null if no match
071 */
072 String lookup(String key);
073
074 /**
075 * Looks up a String key to a String value possibly using the current LogEvent.
076 * <p>
077 * The internal implementation may use any mechanism to return the value.
078 * The simplest implementation is to use a Map. However, virtually any
079 * implementation is possible.
080 * </p>
081 * <p>
082 * For example, it would be possible to implement a lookup that used the
083 * key as a primary key, and looked up the value on demand from the database
084 * Or, a numeric based implementation could be created that treats the key
085 * as an integer, increments the value and return the result as a string -
086 * converting 1 to 2, 15 to 16 etc.
087 * </p>
088 * <p>
089 * This method always returns a String, regardless of
090 * the underlying data, by converting it as necessary. For example:
091 * </p>
092 * <pre>
093 * Map<String, Object> map = new HashMap<String, Object>();
094 * map.put("number", new Integer(2));
095 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
096 * </pre>
097 * @param event The current LogEvent.
098 * @param key the key to be looked up, may be null
099 * @return the matching value, null if no match
100 */
101 String lookup(LogEvent event, String key);
102 }