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 *      https://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 */
017
018package org.apache.commons.text.lookup;
019
020import java.util.function.UnaryOperator;
021
022/**
023 * Lookups a String key for a String value.
024 * <p>
025 * This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create
026 * the result on demand based on the key.
027 * </p>
028 * <p>
029 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value
030 * on demand from the database.
031 * </p>
032 *
033 * @since 1.3
034 */
035@FunctionalInterface
036public interface StringLookup extends UnaryOperator<String> {
037
038    /**
039     * Looks up a String key to provide a String value.
040     * <p>
041     * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
042     * Map. However, virtually any implementation is possible.
043     * </p>
044     * <p>
045     * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
046     * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
047     * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
048     * </p>
049     * <p>
050     * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
051     * example:
052     * </p>
053     *
054     * <pre>
055     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
056     * map.put("number", Integer.valueOf(2));
057     * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
058     * </pre>
059     *
060     * @param key the key to look up, may be null.
061     * @return The matching value, null if no match.
062     * @since 1.14.0
063     */
064    @Override
065    default String apply(final String key) {
066        return lookup(key);
067    }
068
069    /**
070     * Looks up a String key to provide a String value.
071     * <p>
072     * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
073     * Map. However, virtually any implementation is possible.
074     * </p>
075     * <p>
076     * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
077     * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
078     * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
079     * </p>
080     * <p>
081     * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
082     * example:
083     * </p>
084     *
085     * <pre>
086     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
087     * map.put("number", Integer.valueOf(2));
088     * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
089     * </pre>
090     *
091     * @param key the key to look up, may be null.
092     * @return The matching value, null if no match.
093     * @deprecated Use {@link #apply(String)}.
094     */
095    @Deprecated
096    String lookup(String key);
097}