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 * This class comes complete with various factory methods.
029 * If these do not suffice, you can subclass and implement your own matcher.
030 * <p>
031 * For example, it would be possible to implement a lookup that used the
032 * key as a primary key, and looked up the value on demand from the database
033 *
034 * @author Apache Software Foundation
035 * @version $Id$
036 */
037 public interface StrLookup {
038 /**
039 * Looks up a String key to a String value.
040 * <p>
041 * The internal implementation may use any mechanism to return the value.
042 * The simplest implementation is to use a Map. However, virtually any
043 * implementation is possible.
044 * <p>
045 * For example, it would be possible to implement a lookup that used the
046 * key as a primary key, and looked up the value on demand from the database
047 * Or, a numeric based implementation could be created that treats the key
048 * as an integer, increments the value and return the result as a string -
049 * converting 1 to 2, 15 to 16 etc.
050 * <p>
051 * The {@link #lookup(String)} method always returns a String, regardless of
052 * the underlying data, by converting it as necessary. For example:
053 * <pre>
054 * Map<String, Object> map = new HashMap<String, Object>();
055 * map.put("number", new Integer(2));
056 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
057 * </pre>
058 * @param key the key to be looked up, may be null
059 * @return the matching value, null if no match
060 */
061 String lookup(String key);
062
063 /**
064 * Looks up a String key to a String value possibly using the current LogEvent.
065 * <p>
066 * The internal implementation may use any mechanism to return the value.
067 * The simplest implementation is to use a Map. However, virtually any
068 * implementation is possible.
069 * <p>
070 * For example, it would be possible to implement a lookup that used the
071 * key as a primary key, and looked up the value on demand from the database
072 * Or, a numeric based implementation could be created that treats the key
073 * as an integer, increments the value and return the result as a string -
074 * converting 1 to 2, 15 to 16 etc.
075 * <p>
076 * The {@link #lookup(String)} method always returns a String, regardless of
077 * the underlying data, by converting it as necessary. For example:
078 * <pre>
079 * Map<String, Object> map = new HashMap<String, Object>();
080 * map.put("number", new Integer(2));
081 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
082 * </pre>
083 * @param event The current LogEvent.
084 * @param key the key to be looked up, may be null
085 * @return the matching value, null if no match
086 */
087 String lookup(LogEvent event, String key);
088 }