    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&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
    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&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
    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    }