/*
* 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.commons.lang3.text;
import java.util.Map;
/**
* 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>
* This class comes complete with various factory methods.
* If these do not suffice, you can subclass and implement your own matcher.
* <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
*
* @since 2.2
* @version $Id: StrLookup.java 1153484 2011-08-03 13:39:42Z ggregory $
*/
public abstract class StrLookup<V> {
/**
* Lookup that always returns null.
*/
private static final StrLookup<String> NONE_LOOKUP;
/**
* Lookup that uses System properties.
*/
private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP;
static {
NONE_LOOKUP = new MapStrLookup<String>(null);
StrLookup<String> lookup = null;
try {
final Map<?, ?> propMap = System.getProperties();
@SuppressWarnings("unchecked") // System property keys and values are always Strings
final Map<String, String> properties = (Map<String, String>) propMap;
lookup = new MapStrLookup<String>(properties);
} catch (SecurityException ex) {
lookup = NONE_LOOKUP;
}
SYSTEM_PROPERTIES_LOOKUP = lookup;
}
//-----------------------------------------------------------------------
/**
* Returns a lookup which always returns null.
*
* @return a lookup that always returns null, not null
*/
public static StrLookup<?> noneLookup() {
return NONE_LOOKUP;
}
/**
* Returns a lookup which uses {@link System#getProperties() System properties}
* to lookup the key to value.
* <p>
* If a security manager blocked access to system properties, then null will
* be returned from every lookup.
* <p>
* If a null key is used, this lookup will throw a NullPointerException.
*
* @return a lookup using system properties, not null
*/
public static StrLookup<String> systemPropertiesLookup() {
return SYSTEM_PROPERTIES_LOOKUP;
}
/**
* Returns a lookup which looks up values using a map.
* <p>
* If the map is null, then null will be returned from every lookup.
* The map result object is converted to a string using toString().
*
* @param <V> the type of the values supported by the lookup
* @param map the map of keys to values, may be null
* @return a lookup using the map, not null
*/
public static <V> StrLookup<V> mapLookup(Map<String, V> map) {
return new MapStrLookup<V>(map);
}
//-----------------------------------------------------------------------
/**
* Constructor.
*/
protected StrLookup() {
super();
}
/**
* 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>
* 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>
* The {@link #lookup(String)} method always returns a String, regardless of
* the underlying data, by converting it as necessary. For example:
* <pre>
* Map<String, Object> map = new HashMap<String, Object>();
* map.put("number", Integer.valueOf(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
*/
public abstract String lookup(String key);
//-----------------------------------------------------------------------
/**
* Lookup implementation that uses a Map.
*/
static class MapStrLookup<V> extends StrLookup<V> {
/** Map keys are variable names and value. */
private final Map<String, V> map;
/**
* Creates a new instance backed by a Map.
*
* @param map the map of keys to values, may be null
*/
MapStrLookup(Map<String, V> map) {
this.map = map;
}
/**
* Looks up a String key to a String value using the map.
* <p>
* If the map is null, then null is returned.
* The map result object is converted to a string using toString().
*
* @param key the key to be looked up, may be null
* @return the matching value, null if no match
*/
@Override
public String lookup(String key) {
if (map == null) {
return null;
}
Object obj = map.get(key);
if (obj == null) {
return null;
}
return obj.toString();
}
}
}