    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;
    020
    021import org.apache.commons.lang3.SystemProperties;
    022
    023/**
    024 * Lookup a String key to a String value.
    025 * <p>
    026 * This class represents the simplest form of a string to string map.
    027 * It has a benefit over a map in that it can create the result on
    028 * demand based on the key.
    029 * </p>
    030 * <p>
    031 * This class comes complete with various factory methods.
    032 * If these do not suffice, you can subclass and implement your own matcher.
    033 * </p>
    034 * <p>
    035 * For example, it would be possible to implement a lookup that used the
    036 * key as a primary key, and looked up the value on demand from the database.
    037 * </p>
    038 *
    039 * @param <V> Unused.
    040 * @since 2.2
    041 * @deprecated As of 3.6, use Apache Commons Text
    042 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/lookup/StringLookupFactory.html">
    043 * StringLookupFactory</a> instead
    044 */
    045@Deprecated
    046public abstract class StrLookup<V> {
    047
    048    /**
    049     * Lookup that always returns null.
    050     */
    051    private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null);
    052
    053    /**
    054     * Lookup based on system properties.
    055     */
    056    private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup();
    057
    058    /**
    059     * Returns a lookup which always returns null.
    060     *
    061     * @return a lookup that always returns null, not null
    062     */
    063    public static StrLookup<?> noneLookup() {
    064        return NONE_LOOKUP;
    065    }
    066
    067    /**
    068     * Returns a new lookup which uses a copy of the current
    069     * {@link System#getProperties() System properties}.
    070     * <p>
    071     * If a security manager blocked access to system properties, then null will
    072     * be returned from every lookup.
    073     * </p>
    074     * <p>
    075     * If a null key is used, this lookup will throw a NullPointerException.
    076     * </p>
    077     *
    078     * @return a lookup using system properties, not null
    079     */
    080    public static StrLookup<String> systemPropertiesLookup() {
    081        return SYSTEM_PROPERTIES_LOOKUP;
    082    }
    083
    084    /**
    085     * Returns a lookup which looks up values using a map.
    086     * <p>
    087     * If the map is null, then null will be returned from every lookup.
    088     * The map result object is converted to a string using toString().
    089     * </p>
    090     *
    091     * @param <V> the type of the values supported by the lookup
    092     * @param map  the map of keys to values, may be null
    093     * @return a lookup using the map, not null
    094     */
    095    public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
    096        return new MapStrLookup<>(map);
    097    }
    098
    099    /**
    100     * Constructor.
    101     */
    102    protected StrLookup() {
    103    }
    104
    105    /**
    106     * Looks up a String key to a String value.
    107     * <p>
    108     * The internal implementation may use any mechanism to return the value.
    109     * The simplest implementation is to use a Map. However, virtually any
    110     * implementation is possible.
    111     * </p>
    112     * <p>
    113     * For example, it would be possible to implement a lookup that used the
    114     * key as a primary key, and looked up the value on demand from the database
    115     * Or, a numeric based implementation could be created that treats the key
    116     * as an integer, increments the value and return the result as a string -
    117     * converting 1 to 2, 15 to 16 etc.
    118     * </p>
    119     * <p>
    120     * The {@link #lookup(String)} method always returns a String, regardless of
    121     * the underlying data, by converting it as necessary. For example:
    122     * </p>
    123     * <pre>
    124     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
    125     * map.put("number", Integer.valueOf(2));
    126     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
    127     * </pre>
    128     * @param key  the key to be looked up, may be null
    129     * @return the matching value, null if no match
    130     */
    131    public abstract String lookup(String key);
    132
    133    /**
    134     * Lookup implementation that uses a Map.
    135     *
    136     * @param <V> the type of mapped values.
    137     */
    138    static class MapStrLookup<V> extends StrLookup<V> {
    139
    140        /** Map keys are variable names and value. */
    141        private final Map<String, V> map;
    142
    143        /**
    144         * Creates a new instance backed by a Map.
    145         *
    146         * @param map  the map of keys to values, may be null
    147         */
    148        MapStrLookup(final Map<String, V> map) {
    149            this.map = map;
    150        }
    151
    152        /**
    153         * Looks up a String key to a String value using the map.
    154         * <p>
    155         * If the map is null, then null is returned.
    156         * The map result object is converted to a string using toString().
    157         * </p>
    158         *
    159         * @param key  the key to be looked up, may be null
    160         * @return the matching value, null if no match
    161         */
    162        @Override
    163        public String lookup(final String key) {
    164            if (map == null) {
    165                return null;
    166            }
    167            final Object obj = map.get(key);
    168            if (obj == null) {
    169                return null;
    170            }
    171            return obj.toString();
    172        }
    173    }
    174
    175    /**
    176     * Lookup implementation based on system properties.
    177     */
    178    private static class SystemPropertiesStrLookup extends StrLookup<String> {
    179        /**
    180         * {@inheritDoc} This implementation directly accesses system properties.
    181         */
    182        @Override
    183        public String lookup(final String key) {
    184            return SystemProperties.getProperty(key);
    185        }
    186    }
    187}