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