Reusable SoftHashMap utility class

util/src/org/aspectj/util/SoftHashMap.java

@@ -0,0 +1,95 @@
+/* *******************************************************************
+ * Copyright (c) 2017 Contributors
+ * All rights reserved. 
+ * This program and the accompanying materials are made available 
+ * under the terms of the Eclipse Public License v1.0 
+ * which accompanies this distribution and is available at 
+ * http://www.eclipse.org/legal/epl-v10.html 
+ * ******************************************************************/package org.aspectj.util;
+
+import java.lang.ref.*;
+import java.util.*;
+
+public class SoftHashMap<K,V> extends AbstractMap<K,V> {
+	private Map<K, SpecialValue> map;
+	private ReferenceQueue<? super V> rq = new ReferenceQueue<>();
+
+	public SoftHashMap() {
+		this.map = new HashMap<K,SpecialValue>();
+	}
+	
+	class SpecialValue extends SoftReference<V> {
+		private final K key;
+
+		SpecialValue(K k, V v) {
+			super(v, rq);
+			this.key = k;
+		}
+	}
+
+	@SuppressWarnings("unchecked")
+	private void processQueue() {
+		SpecialValue sv = null;
+		while ((sv = (SpecialValue)rq.poll()) != null) {
+			map.remove(sv.key);
+		}
+	}
+
+	@Override
+	public V get(Object key) {
+		SpecialValue ref = map.get(key);
+		if (ref == null) {
+			map.remove(key);
+			return null;
+		}
+		V value = ref.get();
+		if (value == null) {
+			map.remove(ref.key);
+			return null;
+		}
+		return value;
+	}
+
+	@Override
+	public V put(K k, V v) {
+		processQueue();
+		SpecialValue sv = new SpecialValue(k, v);
+		SpecialValue result = map.put(k, sv);
+		return (result == null ? null : result.get());
+	}
+
+	@Override
+	public java.util.Set<Map.Entry<K,V>> entrySet() {
+		if (map.isEmpty()) { return Collections.<K,V>emptyMap().entrySet(); }
+		Map<K,V> currentContents = new HashMap<K,V>();
+		for (Map.Entry<K,SpecialValue> entry: map.entrySet()) {
+			V currentValueForEntry = entry.getValue().get();
+			if (currentValueForEntry != null) {
+				currentContents.put(entry.getKey(), currentValueForEntry);
+			}
+		}
+		return currentContents.entrySet();
+	}
+
+	@Override
+	public void clear() {
+		processQueue();
+		map.clear();
+	}
+
+	@Override
+	public int size() {
+		processQueue();
+		return map.size();
+	}
+
+	@Override
+	public V remove(Object k) {
+		processQueue();
+		SpecialValue ref = map.remove(k);
+		if (ref == null) {
+			return null;
+		}
+		return ref.get();
+	}
+}