https://github.com/spring-projects/spring-framework: Spring Core (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.
 */

package org.springframework.util;

import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Function;

import org.springframework.lang.Nullable;


LinkedHashMap variant that stores String keys in a case-insensitive manner, for example for key-based access in a results table. 
Preserves the original order as well as the original casing of keys,
while allowing for contains, get and remove calls with any case of key.

Does not support null keys. 
Author:Juergen Hoeller, Phillip Webb
Type parameters:
  • <V> – the value type
Since:3.0
/**
 * {@link LinkedHashMap} variant that stores String keys in a case-insensitive
 * manner, for example for key-based access in a results table.
 *
 * <p>Preserves the original order as well as the original casing of keys,
 * while allowing for contains, get and remove calls with any case of key.
 *
 * <p>Does <i>not</i> support {@code null} keys.
 *
 * @author Juergen Hoeller
 * @author Phillip Webb
 * @since 3.0
 * @param <V> the value type
 */
@SuppressWarnings("serial")
public class LinkedCaseInsensitiveMap<V> implements Map<String, V>, Serializable, Cloneable {

	private final LinkedHashMap<String, V> targetMap;

	private final HashMap<String, String> caseInsensitiveKeys;

	private final Locale locale;

	@Nullable
	private transient volatile Set<String> keySet;

	@Nullable
	private transient volatile Collection<V> values;

	@Nullable
	private transient volatile Set<Entry<String, V>> entrySet;


	
Create a new LinkedCaseInsensitiveMap that stores case-insensitive keys
according to the default Locale (by default in lower case).

See Also:
  • convertKey(String)
/**
	 * Create a new LinkedCaseInsensitiveMap that stores case-insensitive keys
	 * according to the default Locale (by default in lower case).
	 * @see #convertKey(String)
	 */
	public LinkedCaseInsensitiveMap() {
		this((Locale) null);
	}

	
Create a new LinkedCaseInsensitiveMap that stores case-insensitive keys
according to the given Locale (in lower case).

Params:
  • locale – the Locale to use for case-insensitive key conversion
See Also:
/**
	 * Create a new LinkedCaseInsensitiveMap that stores case-insensitive keys
	 * according to the given Locale (in lower case).
	 * @param locale the Locale to use for case-insensitive key conversion
	 * @see #convertKey(String)
	 */
	public LinkedCaseInsensitiveMap(@Nullable Locale locale) {
		this(12, locale);  // equivalent to LinkedHashMap's initial capacity of 16
	}

	
Create a new LinkedCaseInsensitiveMap that wraps a LinkedHashMap with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected, storing case-insensitive keys according to the default Locale (in lower case). 
Params:
  • expectedSize – the expected number of elements (with a corresponding
capacity to be derived so that no resize/rehash operations are needed)
See Also:
/**
	 * Create a new LinkedCaseInsensitiveMap that wraps a {@link LinkedHashMap}
	 * with an initial capacity that can accommodate the specified number of
	 * elements without any immediate resize/rehash operations to be expected,
	 * storing case-insensitive keys according to the default Locale (in lower case).
	 * @param expectedSize the expected number of elements (with a corresponding
	 * capacity to be derived so that no resize/rehash operations are needed)
	 * @see CollectionUtils#newHashMap(int)
	 * @see #convertKey(String)
	 */
	public LinkedCaseInsensitiveMap(int expectedSize) {
		this(expectedSize, null);
	}

	
Create a new LinkedCaseInsensitiveMap that wraps a LinkedHashMap with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected, storing case-insensitive keys according to the given Locale (in lower case). 
Params:
  • expectedSize – the expected number of elements (with a corresponding
capacity to be derived so that no resize/rehash operations are needed)
  • locale – the Locale to use for case-insensitive key conversion
See Also:
/**
	 * Create a new LinkedCaseInsensitiveMap that wraps a {@link LinkedHashMap}
	 * with an initial capacity that can accommodate the specified number of
	 * elements without any immediate resize/rehash operations to be expected,
	 * storing case-insensitive keys according to the given Locale (in lower case).
	 * @param expectedSize the expected number of elements (with a corresponding
	 * capacity to be derived so that no resize/rehash operations are needed)
	 * @param locale the Locale to use for case-insensitive key conversion
	 * @see CollectionUtils#newHashMap(int)
	 * @see #convertKey(String)
	 */
	public LinkedCaseInsensitiveMap(int expectedSize, @Nullable Locale locale) {
		this.targetMap = new LinkedHashMap<String, V>(
				(int) (expectedSize / CollectionUtils.DEFAULT_LOAD_FACTOR), CollectionUtils.DEFAULT_LOAD_FACTOR) {
			@Override
			public boolean containsKey(Object key) {
				return LinkedCaseInsensitiveMap.this.containsKey(key);
			}
			@Override
			protected boolean removeEldestEntry(Map.Entry<String, V> eldest) {
				boolean doRemove = LinkedCaseInsensitiveMap.this.removeEldestEntry(eldest);
				if (doRemove) {
					removeCaseInsensitiveKey(eldest.getKey());
				}
				return doRemove;
			}
		};
		this.caseInsensitiveKeys = CollectionUtils.newHashMap(expectedSize);
		this.locale = (locale != null ? locale : Locale.getDefault());
	}

	
Copy constructor.

/**
	 * Copy constructor.
	 */
	@SuppressWarnings("unchecked")
	private LinkedCaseInsensitiveMap(LinkedCaseInsensitiveMap<V> other) {
		this.targetMap = (LinkedHashMap<String, V>) other.targetMap.clone();
		this.caseInsensitiveKeys = (HashMap<String, String>) other.caseInsensitiveKeys.clone();
		this.locale = other.locale;
	}


	// Implementation of java.util.Map

	@Override
	public int size() {
		return this.targetMap.size();
	}

	@Override
	public boolean isEmpty() {
		return this.targetMap.isEmpty();
	}

	@Override
	public boolean containsKey(Object key) {
		return (key instanceof String && this.caseInsensitiveKeys.containsKey(convertKey((String) key)));
	}

	@Override
	public boolean containsValue(Object value) {
		return this.targetMap.containsValue(value);
	}

	@Override
	@Nullable
	public V get(Object key) {
		if (key instanceof String) {
			String caseInsensitiveKey = this.caseInsensitiveKeys.get(convertKey((String) key));
			if (caseInsensitiveKey != null) {
				return this.targetMap.get(caseInsensitiveKey);
			}
		}
		return null;
	}

	@Override
	@Nullable
	public V getOrDefault(Object key, V defaultValue) {
		if (key instanceof String) {
			String caseInsensitiveKey = this.caseInsensitiveKeys.get(convertKey((String) key));
			if (caseInsensitiveKey != null) {
				return this.targetMap.get(caseInsensitiveKey);
			}
		}
		return defaultValue;
	}

	@Override
	@Nullable
	public V put(String key, @Nullable V value) {
		String oldKey = this.caseInsensitiveKeys.put(convertKey(key), key);
		V oldKeyValue = null;
		if (oldKey != null && !oldKey.equals(key)) {
			oldKeyValue = this.targetMap.remove(oldKey);
		}
		V oldValue = this.targetMap.put(key, value);
		return (oldKeyValue != null ? oldKeyValue : oldValue);
	}

	@Override
	public void putAll(Map<? extends String, ? extends V> map) {
		if (map.isEmpty()) {
			return;
		}
		map.forEach(this::put);
	}

	@Override
	@Nullable
	public V putIfAbsent(String key, @Nullable V value) {
		String oldKey = this.caseInsensitiveKeys.putIfAbsent(convertKey(key), key);
		if (oldKey != null) {
			return this.targetMap.get(oldKey);
		}
		return this.targetMap.putIfAbsent(key, value);
	}

	@Override
	@Nullable
	public V computeIfAbsent(String key, Function<? super String, ? extends V> mappingFunction) {
		String oldKey = this.caseInsensitiveKeys.putIfAbsent(convertKey(key), key);
		if (oldKey != null) {
			return this.targetMap.get(oldKey);
		}
		return this.targetMap.computeIfAbsent(key, mappingFunction);
	}

	@Override
	@Nullable
	public V remove(Object key) {
		if (key instanceof String) {
			String caseInsensitiveKey = removeCaseInsensitiveKey((String) key);
			if (caseInsensitiveKey != null) {
				return this.targetMap.remove(caseInsensitiveKey);
			}
		}
		return null;
	}

	@Override
	public void clear() {
		this.caseInsensitiveKeys.clear();
		this.targetMap.clear();
	}

	@Override
	public Set<String> keySet() {
		Set<String> keySet = this.keySet;
		if (keySet == null) {
			keySet = new KeySet(this.targetMap.keySet());
			this.keySet = keySet;
		}
		return keySet;
	}

	@Override
	public Collection<V> values() {
		Collection<V> values = this.values;
		if (values == null) {
			values = new Values(this.targetMap.values());
			this.values = values;
		}
		return values;
	}

	@Override
	public Set<Entry<String, V>> entrySet() {
		Set<Entry<String, V>> entrySet = this.entrySet;
		if (entrySet == null) {
			entrySet = new EntrySet(this.targetMap.entrySet());
			this.entrySet = entrySet;
		}
		return entrySet;
	}

	@Override
	public LinkedCaseInsensitiveMap<V> clone() {
		return new LinkedCaseInsensitiveMap<>(this);
	}

	@Override
	public boolean equals(@Nullable Object other) {
		return (this == other || this.targetMap.equals(other));
	}

	@Override
	public int hashCode() {
		return this.targetMap.hashCode();
	}

	@Override
	public String toString() {
		return this.targetMap.toString();
	}


	// Specific to LinkedCaseInsensitiveMap

	
Return the locale used by this LinkedCaseInsensitiveMap. Used for case-insensitive key conversion. 
See Also:
Since:4.3.10
/**
	 * Return the locale used by this {@code LinkedCaseInsensitiveMap}.
	 * Used for case-insensitive key conversion.
	 * @since 4.3.10
	 * @see #LinkedCaseInsensitiveMap(Locale)
	 * @see #convertKey(String)
	 */
	public Locale getLocale() {
		return this.locale;
	}

	
Convert the given key to a case-insensitive key.

The default implementation converts the key
to lower-case according to this Map's Locale.

Params:
  • key – the user-specified key
See Also:
Returns:the key to use for storing
/**
	 * Convert the given key to a case-insensitive key.
	 * <p>The default implementation converts the key
	 * to lower-case according to this Map's Locale.
	 * @param key the user-specified key
	 * @return the key to use for storing
	 * @see String#toLowerCase(Locale)
	 */
	protected String convertKey(String key) {
		return key.toLowerCase(getLocale());
	}

	
Determine whether this map should remove the given eldest entry.

Params:
  • eldest – the candidate entry
See Also:
Returns:true for removing it, false for keeping it
/**
	 * Determine whether this map should remove the given eldest entry.
	 * @param eldest the candidate entry
	 * @return {@code true} for removing it, {@code false} for keeping it
	 * @see LinkedHashMap#removeEldestEntry
	 */
	protected boolean removeEldestEntry(Map.Entry<String, V> eldest) {
		return false;
	}

	@Nullable
	private String removeCaseInsensitiveKey(String key) {
		return this.caseInsensitiveKeys.remove(convertKey(key));
	}


	private class KeySet extends AbstractSet<String> {

		private final Set<String> delegate;

		KeySet(Set<String> delegate) {
			this.delegate = delegate;
		}

		@Override
		public int size() {
			return this.delegate.size();
		}

		@Override
		public boolean contains(Object o) {
			return this.delegate.contains(o);
		}

		@Override
		public Iterator<String> iterator() {
			return new KeySetIterator();
		}

		@Override
		public boolean remove(Object o) {
			return LinkedCaseInsensitiveMap.this.remove(o) != null;
		}

		@Override
		public void clear() {
			LinkedCaseInsensitiveMap.this.clear();
		}

		@Override
		public Spliterator<String> spliterator() {
			return this.delegate.spliterator();
		}

		@Override
		public void forEach(Consumer<? super String> action) {
			this.delegate.forEach(action);
		}
	}


	private class Values extends AbstractCollection<V> {

		private final Collection<V> delegate;

		Values(Collection<V> delegate) {
			this.delegate = delegate;
		}

		@Override
		public int size() {
			return this.delegate.size();
		}

		@Override
		public boolean contains(Object o) {
			return this.delegate.contains(o);
		}

		@Override
		public Iterator<V> iterator() {
			return new ValuesIterator();
		}

		@Override
		public void clear() {
			LinkedCaseInsensitiveMap.this.clear();
		}

		@Override
		public Spliterator<V> spliterator() {
			return this.delegate.spliterator();
		}

		@Override
		public void forEach(Consumer<? super V> action) {
			this.delegate.forEach(action);
		}
	}


	private class EntrySet extends AbstractSet<Entry<String, V>> {

		private final Set<Entry<String, V>> delegate;

		public EntrySet(Set<Entry<String, V>> delegate) {
			this.delegate = delegate;
		}

		@Override
		public int size() {
			return this.delegate.size();
		}

		@Override
		public boolean contains(Object o) {
			return this.delegate.contains(o);
		}

		@Override
		public Iterator<Entry<String, V>> iterator() {
			return new EntrySetIterator();
		}

		@Override
		@SuppressWarnings("unchecked")
		public boolean remove(Object o) {
			if (this.delegate.remove(o)) {
				removeCaseInsensitiveKey(((Map.Entry<String, V>) o).getKey());
				return true;
			}
			return false;
		}

		@Override
		public void clear() {
			this.delegate.clear();
			caseInsensitiveKeys.clear();
		}

		@Override
		public Spliterator<Entry<String, V>> spliterator() {
			return this.delegate.spliterator();
		}

		@Override
		public void forEach(Consumer<? super Entry<String, V>> action) {
			this.delegate.forEach(action);
		}
	}


	private abstract class EntryIterator<T> implements Iterator<T> {

		private final Iterator<Entry<String, V>> delegate;

		@Nullable
		private Entry<String, V> last;

		public EntryIterator() {
			this.delegate = targetMap.entrySet().iterator();
		}

		protected Entry<String, V> nextEntry() {
			Entry<String, V> entry = this.delegate.next();
			this.last = entry;
			return entry;
		}

		@Override
		public boolean hasNext() {
			return this.delegate.hasNext();
		}

		@Override
		public void remove() {
			this.delegate.remove();
			if (this.last != null) {
				removeCaseInsensitiveKey(this.last.getKey());
				this.last = null;
			}
		}
	}


	private class KeySetIterator extends EntryIterator<String> {

		@Override
		public String next() {
			return nextEntry().getKey();
		}
	}


	private class ValuesIterator extends EntryIterator<V> {

		@Override
		public V next() {
			return nextEntry().getValue();
		}
	}


	private class EntrySetIterator extends EntryIterator<Entry<String, V>> {

		@Override
		public Entry<String, V> next() {
			return nextEntry();
		}
	}

}