org.apache.logging.log4j.core.lookup.StrLookup Maven / Gradle / Ivy
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/*
* 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
*
*/
public interface StrLookup {
/**
* 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"));
*
* @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"));
*
* @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);
}