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 */ 017package org.apache.commons.lang3.text; 018 019import java.util.Map; 020import java.util.Objects; 021 022import org.apache.commons.lang3.SystemProperties; 023 024/** 025 * Lookup a String key to a String value. 026 * <p> 027 * This class represents the simplest form of a string to string map. 028 * It has a benefit over a map in that it can create the result on 029 * demand based on the key. 030 * </p> 031 * <p> 032 * This class comes complete with various factory methods. 033 * If these do not suffice, you can subclass and implement your own matcher. 034 * </p> 035 * <p> 036 * For example, it would be possible to implement a lookup that used the 037 * key as a primary key, and looked up the value on demand from the database. 038 * </p> 039 * 040 * @param <V> Unused. 041 * @since 2.2 042 * @deprecated As of 3.6, use Apache Commons Text 043 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/lookup/StringLookupFactory.html"> 044 * StringLookupFactory</a> instead 045 */ 046@Deprecated 047public abstract class StrLookup<V> { 048 049 /** 050 * Lookup implementation that uses a Map. 051 * 052 * @param <V> the type of mapped values. 053 */ 054 static class MapStrLookup<V> extends StrLookup<V> { 055 056 /** Map keys are variable names and value. */ 057 private final Map<String, V> map; 058 059 /** 060 * Creates a new instance backed by a Map. 061 * 062 * @param map the map of keys to values, may be null 063 */ 064 MapStrLookup(final Map<String, V> map) { 065 this.map = map; 066 } 067 068 /** 069 * Looks up a String key to a String value using the map. 070 * <p> 071 * If the map is null, then null is returned. 072 * The map result object is converted to a string using toString(). 073 * </p> 074 * 075 * @param key the key to be looked up, may be null 076 * @return the matching value, null if no match 077 */ 078 @Override 079 public String lookup(final String key) { 080 if (map == null) { 081 return null; 082 } 083 return Objects.toString(map.get(key), null); 084 } 085 } 086 087 /** 088 * Lookup implementation based on system properties. 089 */ 090 private static final class SystemPropertiesStrLookup extends StrLookup<String> { 091 /** 092 * {@inheritDoc} This implementation directly accesses system properties. 093 */ 094 @Override 095 public String lookup(final String key) { 096 return SystemProperties.getProperty(key); 097 } 098 } 099 100 /** 101 * Lookup that always returns null. 102 */ 103 private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null); 104 105 /** 106 * Lookup based on system properties. 107 */ 108 private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup(); 109 110 /** 111 * Returns a lookup which looks up values using a map. 112 * <p> 113 * If the map is null, then null will be returned from every lookup. 114 * The map result object is converted to a string using toString(). 115 * </p> 116 * 117 * @param <V> the type of the values supported by the lookup 118 * @param map the map of keys to values, may be null 119 * @return a lookup using the map, not null 120 */ 121 public static <V> StrLookup<V> mapLookup(final Map<String, V> map) { 122 return new MapStrLookup<>(map); 123 } 124 125 /** 126 * Returns a lookup which always returns null. 127 * 128 * @return a lookup that always returns null, not null 129 */ 130 public static StrLookup<?> noneLookup() { 131 return NONE_LOOKUP; 132 } 133 134 /** 135 * Returns a new lookup which uses a copy of the current 136 * {@link System#getProperties() System properties}. 137 * <p> 138 * If a security manager blocked access to system properties, then null will 139 * be returned from every lookup. 140 * </p> 141 * <p> 142 * If a null key is used, this lookup will throw a NullPointerException. 143 * </p> 144 * 145 * @return a lookup using system properties, not null 146 */ 147 public static StrLookup<String> systemPropertiesLookup() { 148 return SYSTEM_PROPERTIES_LOOKUP; 149 } 150 151 /** 152 * Constructs a new instance. 153 */ 154 protected StrLookup() { 155 } 156 157 /** 158 * Looks up a String key to a String value. 159 * <p> 160 * The internal implementation may use any mechanism to return the value. 161 * The simplest implementation is to use a Map. However, virtually any 162 * implementation is possible. 163 * </p> 164 * <p> 165 * For example, it would be possible to implement a lookup that used the 166 * key as a primary key, and looked up the value on demand from the database 167 * Or, a numeric based implementation could be created that treats the key 168 * as an integer, increments the value and return the result as a string - 169 * converting 1 to 2, 15 to 16 etc. 170 * </p> 171 * <p> 172 * The {@link #lookup(String)} method always returns a String, regardless of 173 * the underlying data, by converting it as necessary. For example: 174 * </p> 175 * <pre>{@code 176 * Map<String, Object> map = new HashMap<String, Object>(); 177 * map.put("number", Integer.valueOf(2)); 178 * assertEquals("2", StrLookup.mapLookup(map).lookup("number")); 179 * }</pre> 180 * @param key the key to be looked up, may be null 181 * @return the matching value, null if no match 182 */ 183 public abstract String lookup(String key); 184}