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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package org.apache.commons.lang3.text;

import java.util.Map;

Lookup a String key to a String value.

This class represents the simplest form of a string to string map.
It has a benefit over a map in that it can create the result on
demand based on the key.

This class comes complete with various factory methods.
If these do not suffice, you can subclass and implement your own matcher.

For example, it would be possible to implement a lookup that used the
key as a primary key, and looked up the value on demand from the database.
Type parameters:
<V> – Unused.
Since:
2.2
Deprecated:
as of 3.6, use commons-text

StringLookupFactory instead/**
 * Lookup a String key to a String value.
 * <p>
 * This class represents the simplest form of a string to string map.
 * It has a benefit over a map in that it can create the result on
 * demand based on the key.
 * <p>
 * This class comes complete with various factory methods.
 * If these do not suffice, you can subclass and implement your own matcher.
 * <p>
 * For example, it would be possible to implement a lookup that used the
 * key as a primary key, and looked up the value on demand from the database.
 *
 * @param <V> Unused.
 * @since 2.2
 * @deprecated as of 3.6, use commons-text
 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/StringLookupFactory.html">
 * StringLookupFactory</a> instead
 */
@Deprecated
public abstract class StrLookup<V> {

    
Lookup that always returns null.
/**
     * Lookup that always returns null.
     */
    private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null);

    
Lookup based on system properties.
/**
     * Lookup based on system properties.
     */
    private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup();

    //-----------------------------------------------------------------------
    
Returns a lookup which always returns null.
Returns:
a lookup that always returns null, not null/**
     * Returns a lookup which always returns null.
     *
     * @return a lookup that always returns null, not null
     */
    public static StrLookup<?> noneLookup() {
        return NONE_LOOKUP;
    }

    
Returns a new lookup which uses a copy of the current System properties. 

If a security manager blocked access to system properties, then null will
be returned from every lookup.

If a null key is used, this lookup will throw a NullPointerException.
Returns:
a lookup using system properties, not null/**
     * Returns a new lookup which uses a copy of the current
     * {@link System#getProperties() System properties}.
     * <p>
     * If a security manager blocked access to system properties, then null will
     * be returned from every lookup.
     * <p>
     * If a null key is used, this lookup will throw a NullPointerException.
     *
     * @return a lookup using system properties, not null
     */
    public static StrLookup<String> systemPropertiesLookup() {
        return SYSTEM_PROPERTIES_LOOKUP;
    }

    
Returns a lookup which looks up values using a map.

If the map is null, then null will be returned from every lookup.
The map result object is converted to a string using toString().
Params:
map –  the map of keys to values, may be null
Type parameters:
<V> – the type of the values supported by the lookup
Returns:
a lookup using the map, not null/**
     * Returns a lookup which looks up values using a map.
     * <p>
     * If the map is null, then null will be returned from every lookup.
     * The map result object is converted to a string using toString().
     *
     * @param <V> the type of the values supported by the lookup
     * @param map  the map of keys to values, may be null
     * @return a lookup using the map, not null
     */
    public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
        return new MapStrLookup<>(map);
    }

    //-----------------------------------------------------------------------
    
Constructor.
/**
     * Constructor.
     */
    protected StrLookup() {
        super();
    }

    
Looks up a String key to a String value.

The internal implementation may use any mechanism to return the value.
The simplest implementation is to use a Map. However, virtually any
implementation is possible.

For example, it would be possible to implement a lookup that used the
key as a primary key, and looked up the value on demand from the database
Or, a numeric based implementation could be created that treats the key
as an integer, increments the value and return the result as a string -
converting 1 to 2, 15 to 16 etc.
 The lookup(String) method always returns a String, regardless of the underlying data, by converting it as necessary. For example: 
Map<String, Object> map = new HashMap<String, Object>();
map.put("number", Integer.valueOf(2));
assertEquals("2", StrLookup.mapLookup(map).lookup("number"));

Params:
key –  the key to be looked up, may be null
Returns:
the matching value, null if no match/**
     * Looks up a String key to a String value.
     * <p>
     * The internal implementation may use any mechanism to return the value.
     * The simplest implementation is to use a Map. However, virtually any
     * implementation is possible.
     * <p>
     * For example, it would be possible to implement a lookup that used the
     * key as a primary key, and looked up the value on demand from the database
     * Or, a numeric based implementation could be created that treats the key
     * as an integer, increments the value and return the result as a string -
     * converting 1 to 2, 15 to 16 etc.
     * <p>
     * The {@link #lookup(String)} method always returns a String, regardless of
     * the underlying data, by converting it as necessary. For example:
     * <pre>
     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
     * map.put("number", Integer.valueOf(2));
     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
     * </pre>
     * @param key  the key to be looked up, may be null
     * @return the matching value, null if no match
     */
    public abstract String lookup(String key);

    //-----------------------------------------------------------------------
    
Lookup implementation that uses a Map.
/**
     * Lookup implementation that uses a Map.
     */
    static class MapStrLookup<V> extends StrLookup<V> {

        
Map keys are variable names and value. /** Map keys are variable names and value. */
        private final Map<String, V> map;

        
Creates a new instance backed by a Map.
Params:
map –  the map of keys to values, may be null/**
         * Creates a new instance backed by a Map.
         *
         * @param map  the map of keys to values, may be null
         */
        MapStrLookup(final Map<String, V> map) {
            this.map = map;
        }

        
Looks up a String key to a String value using the map.

If the map is null, then null is returned.
The map result object is converted to a string using toString().
Params:
key –  the key to be looked up, may be null
Returns:
the matching value, null if no match/**
         * Looks up a String key to a String value using the map.
         * <p>
         * If the map is null, then null is returned.
         * The map result object is converted to a string using toString().
         *
         * @param key  the key to be looked up, may be null
         * @return the matching value, null if no match
         */
        @Override
        public String lookup(final String key) {
            if (map == null) {
                return null;
            }
            final Object obj = map.get(key);
            if (obj == null) {
                return null;
            }
            return obj.toString();
        }
    }

    //-----------------------------------------------------------------------
    
Lookup implementation based on system properties.
/**
     * Lookup implementation based on system properties.
     */
    private static class SystemPropertiesStrLookup extends StrLookup<String> {
        
{@inheritDoc} This implementation directly accesses system properties.
/**
         * {@inheritDoc} This implementation directly accesses system properties.
         */
        @Override
        public String lookup(final String key) {
            if (!key.isEmpty()) {
                try {
                    return System.getProperty(key);
                } catch (final SecurityException scex) {
                    // Squelched. All lookup(String) will return null.
                }
            }
            return null;
        }
    }
}