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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.commons.lang3.text;

import java.util.Map;

/**
 * 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 * * @since 2.2 * @version $Id: StrLookup.java 1436770 2013-01-22 07:09:45Z ggregory $ */ public abstract class StrLookup { /** * Lookup that always returns null. */ private static final StrLookup NONE_LOOKUP; /** * Lookup that uses System properties. */ private static final StrLookup SYSTEM_PROPERTIES_LOOKUP; static { NONE_LOOKUP = new MapStrLookup(null); StrLookup lookup = null; try { final Map propMap = System.getProperties(); @SuppressWarnings("unchecked") // System property keys and values are always Strings final Map properties = (Map) propMap; lookup = new MapStrLookup(properties); } catch (final 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. *

* If a security manager blocked access to system properties, then null will * be returned from every lookup. *

* If a null key is used, this lookup will throw a NullPointerException. * * @return a lookup using system properties, not null */ public static StrLookup systemPropertiesLookup() { return SYSTEM_PROPERTIES_LOOKUP; } /** * Returns a lookup which looks up values using a map. *

* 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 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 StrLookup mapLookup(final Map map) { return new MapStrLookup(map); } //----------------------------------------------------------------------- /** * Constructor. */ protected StrLookup() { super(); } /** * 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. *

* The {@link #lookup(String)} method always returns a String, regardless of * the underlying data, by converting it as necessary. For example: *

     * Map map = new HashMap();
     * map.put("number", Integer.valueOf(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 */ public abstract String lookup(String key); //----------------------------------------------------------------------- /** * Lookup implementation that uses a Map. */ static class MapStrLookup extends StrLookup { /** Map keys are variable names and value. */ private final Map map; /** * Creates a new instance backed by a Map. * * @param map the map of keys to values, may be null */ MapStrLookup(final Map map) { this.map = map; } /** * Looks up a String key to a String value using the map. *

* 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(final String key) { if (map == null) { return null; } final Object obj = map.get(key); if (obj == null) { return null; } return obj.toString(); } } }





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