Added MultiValueMap utility methods

org.springframework.core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -16,14 +16,19 @@
 
 package org.springframework.util;
 
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Enumeration;
 import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import java.util.Set;
 
 /**
  * Miscellaneous collection utility methods.
@@ -31,6 +36,7 @@ import java.util.Properties;
  *
  * @author Juergen Hoeller
  * @author Rob Harrop
+ * @author Arjen Poutsma
  * @since 1.1.3
  */
 public abstract class CollectionUtils {
@@ -323,6 +329,35 @@ public abstract class CollectionUtils {
 		return new EnumerationIterator<E>(enumeration);
 	}
 
+	/**
+	 * Adapts a {@code Map<K, List<V>>} to an {@code MultiValueMap<K,V>}.
+	 *
+	 * @param map the map
+	 * @return the multi-value map
+	 */
+	public static <K, V> MultiValueMap<K, V> toMultiValueMap(Map<K, List<V>> map) {
+		return new MultiValueMapAdapter<K, V>(map);
+
+	}
+
+	/**
+	 * Returns an unmodifiable view of the specified multi-value map.
+	 *
+	 * @param  map the map for which an unmodifiable view is to be returned.
+	 * @return an unmodifiable view of the specified multi-value map.
+	 */
+	public static <K,V> MultiValueMap<K,V> unmodifiableMultiValueMap(MultiValueMap<? extends K, ? extends V> map) {
+		Assert.notNull(map, "'map' must not be null");
+		Map<K, List<V>> result = new LinkedHashMap<K, List<V>>(map.size());
+		for (Map.Entry<? extends K, ? extends List<? extends V>> entry : map.entrySet()) {
+			List<V> values = Collections.unmodifiableList(entry.getValue());
+			result.put(entry.getKey(), values);
+		}
+		Map<K, List<V>> unmodifiableMap = Collections.unmodifiableMap(result);
+		return toMultiValueMap(unmodifiableMap);
+	}
+
+
 
 	/**
 	 * Iterator wrapping an Enumeration.
@@ -348,4 +383,117 @@ public abstract class CollectionUtils {
 		}
 	}
 
+	/**
+	 * Adapts a Map to the MultiValueMap contract.
+	 */
+	private static class MultiValueMapAdapter<K, V> implements MultiValueMap<K, V>, Serializable {
+
+		private final Map<K, List<V>> map;
+
+		public MultiValueMapAdapter(Map<K, List<V>> map) {
+			Assert.notNull(map, "'map' must not be null");
+			this.map = map;
+		}
+
+		public void add(K key, V value) {
+			List<V> values = this.map.get(key);
+			if (values == null) {
+				values = new LinkedList<V>();
+				this.map.put(key, values);
+			}
+			values.add(value);
+		}
+
+		public V getFirst(K key) {
+			List<V> values = this.map.get(key);
+			return (values != null ? values.get(0) : null);
+		}
+
+		public void set(K key, V value) {
+			List<V> values = new LinkedList<V>();
+			values.add(value);
+			this.map.put(key, values);
+		}
+
+		public void setAll(Map<K, V> values) {
+			for (Entry<K, V> entry : values.entrySet()) {
+				set(entry.getKey(), entry.getValue());
+			}
+		}
+
+		public Map<K, V> toSingleValueMap() {
+			LinkedHashMap<K, V> singleValueMap = new LinkedHashMap<K,V>(this.map.size());
+			for (Entry<K, List<V>> entry : map.entrySet()) {
+				singleValueMap.put(entry.getKey(), entry.getValue().get(0));
+			}
+			return singleValueMap;
+		}
+
+		public int size() {
+			return this.map.size();
+		}
+
+		public boolean isEmpty() {
+			return this.map.isEmpty();
+		}
+
+		public boolean containsKey(Object key) {
+			return this.map.containsKey(key);
+		}
+
+		public boolean containsValue(Object value) {
+			return this.map.containsValue(value);
+		}
+
+		public List<V> get(Object key) {
+			return this.map.get(key);
+		}
+
+		public List<V> put(K key, List<V> value) {
+			return this.map.put(key, value);
+		}
+
+		public List<V> remove(Object key) {
+			return this.map.remove(key);
+		}
+
+		public void putAll(Map<? extends K, ? extends List<V>> m) {
+			this.map.putAll(m);
+		}
+
+		public void clear() {
+			this.map.clear();
+		}
+
+		public Set<K> keySet() {
+			return this.map.keySet();
+		}
+
+		public Collection<List<V>> values() {
+			return this.map.values();
+		}
+
+		public Set<Entry<K, List<V>>> entrySet() {
+			return this.map.entrySet();
+		}
+
+		@Override
+		public boolean equals(Object other) {
+			if (this == other) {
+				return true;
+			}
+			return map.equals(other);
+		}
+
+		@Override
+		public int hashCode() {
+			return this.map.hashCode();
+		}
+
+		@Override
+		public String toString() {
+			return this.map.toString();
+		}
+	}
+
 }