    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}