/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.lookup;

import org.apache.logging.log4j.core.LogEvent;

Lookup a String key to a String value.

This class represents the simplest form of a string to string map.
It has a benefit over a map in that it can create the result on
demand based on the key.


This class comes complete with various factory methods.
If these do not suffice, you can subclass and implement your own matcher.


For example, it would be possible to implement a lookup that used the
key as a primary key, and looked up the value on demand from the database

/**
 * Lookup a String key to a String value.
 * <p>
 * This class represents the simplest form of a string to string map.
 * It has a benefit over a map in that it can create the result on
 * demand based on the key.
 * </p>
 * <p>
 * This class comes complete with various factory methods.
 * If these do not suffice, you can subclass and implement your own matcher.
 * </p>
 * <p>
 * For example, it would be possible to implement a lookup that used the
 * key as a primary key, and looked up the value on demand from the database
 * </p>
 */
public interface StrLookup {

    
Main plugin category for StrLookup plugins.
Since:
2.1/**
     * Main plugin category for StrLookup plugins.
     *
     * @since 2.1
     */
    String CATEGORY = "Lookup";

    
Looks up a String key to a String value.

The internal implementation may use any mechanism to return the value.
The simplest implementation is to use a Map. However, virtually any
implementation is possible.


For example, it would be possible to implement a lookup that used the
key as a primary key, and looked up the value on demand from the database
Or, a numeric based implementation could be created that treats the key
as an integer, increments the value and return the result as a string -
converting 1 to 2, 15 to 16 etc.


This method always returns a String, regardless of
the underlying data, by converting it as necessary. For example:

Map<String, Object> map = new HashMap<String, Object>();
map.put("number", new Integer(2));
assertEquals("2", StrLookup.mapLookup(map).lookup("number"));

Params:
key –  the key to be looked up, may be null
Returns:
the matching value, null if no match/**
     * Looks up a String key to a String value.
     * <p>
     * The internal implementation may use any mechanism to return the value.
     * The simplest implementation is to use a Map. However, virtually any
     * implementation is possible.
     * </p>
     * <p>
     * For example, it would be possible to implement a lookup that used the
     * key as a primary key, and looked up the value on demand from the database
     * Or, a numeric based implementation could be created that treats the key
     * as an integer, increments the value and return the result as a string -
     * converting 1 to 2, 15 to 16 etc.
     * </p>
     * <p>
     * This method always returns a String, regardless of
     * the underlying data, by converting it as necessary. For example:
     * </p>
     * <pre>
     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
     * map.put("number", new Integer(2));
     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
     * </pre>
     * @param key  the key to be looked up, may be null
     * @return the matching value, null if no match
     */
    String lookup(String key);

    
Looks up a String key to a String value possibly using the current LogEvent.

The internal implementation may use any mechanism to return the value.
The simplest implementation is to use a Map. However, virtually any
implementation is possible.


For example, it would be possible to implement a lookup that used the
key as a primary key, and looked up the value on demand from the database
Or, a numeric based implementation could be created that treats the key
as an integer, increments the value and return the result as a string -
converting 1 to 2, 15 to 16 etc.


This method always returns a String, regardless of
the underlying data, by converting it as necessary. For example:

Map<String, Object> map = new HashMap<String, Object>();
map.put("number", new Integer(2));
assertEquals("2", StrLookup.mapLookup(map).lookup("number"));

Params:
event – The current LogEvent.
key –  the key to be looked up, may be null
Returns:
the matching value, null if no match/**
     * Looks up a String key to a String value possibly using the current LogEvent.
     * <p>
     * The internal implementation may use any mechanism to return the value.
     * The simplest implementation is to use a Map. However, virtually any
     * implementation is possible.
     * </p>
     * <p>
     * For example, it would be possible to implement a lookup that used the
     * key as a primary key, and looked up the value on demand from the database
     * Or, a numeric based implementation could be created that treats the key
     * as an integer, increments the value and return the result as a string -
     * converting 1 to 2, 15 to 16 etc.
     * </p>
     * <p>
     * This method always returns a String, regardless of
     * the underlying data, by converting it as necessary. For example:
     * </p>
     * <pre>
     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
     * map.put("number", new Integer(2));
     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
     * </pre>
     * @param event The current LogEvent.
     * @param key  the key to be looked up, may be null
     * @return the matching value, null if no match
     */
    String lookup(LogEvent event, String key);
}