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 */
017package org.apache.logging.log4j.core.lookup;
018
019import 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 * @version $Id$
035 */
036public interface StrLookup {
037    /**
038     * Looks up a String key to a String value.
039     * <p>
040     * The internal implementation may use any mechanism to return the value.
041     * The simplest implementation is to use a Map. However, virtually any
042     * implementation is possible.
043     * <p>
044     * For example, it would be possible to implement a lookup that used the
045     * key as a primary key, and looked up the value on demand from the database
046     * Or, a numeric based implementation could be created that treats the key
047     * as an integer, increments the value and return the result as a string -
048     * converting 1 to 2, 15 to 16 etc.
049     * <p>
050     * The {@link #lookup(String)} method always returns a String, regardless of
051     * the underlying data, by converting it as necessary. For example:
052     * <pre>
053     * Map<String, Object> map = new HashMap<String, Object>();
054     * map.put("number", new Integer(2));
055     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
056     * </pre>
057     * @param key  the key to be looked up, may be null
058     * @return the matching value, null if no match
059     */
060    String lookup(String key);
061
062    /**
063     * Looks up a String key to a String value possibly using the current LogEvent.
064     * <p>
065     * The internal implementation may use any mechanism to return the value.
066     * The simplest implementation is to use a Map. However, virtually any
067     * implementation is possible.
068     * <p>
069     * For example, it would be possible to implement a lookup that used the
070     * key as a primary key, and looked up the value on demand from the database
071     * Or, a numeric based implementation could be created that treats the key
072     * as an integer, increments the value and return the result as a string -
073     * converting 1 to 2, 15 to 16 etc.
074     * <p>
075     * The {@link #lookup(String)} method always returns a String, regardless of
076     * the underlying data, by converting it as necessary. For example:
077     * <pre>
078     * Map<String, Object> map = new HashMap<String, Object>();
079     * map.put("number", new Integer(2));
080     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
081     * </pre>
082     * @param event The current LogEvent.
083     * @param key  the key to be looked up, may be null
084     * @return the matching value, null if no match
085     */
086    String lookup(LogEvent event, String key);
087}