Apache CXF example source code file (WeakIdentityHashMap.java)

This example Apache CXF source code file (WeakIdentityHashMap.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Apache CXF tags/keywords

collection, identityweakreference, identityweakreference, k, k, map, referencequeue, set, unsupportedoperationexception, util, v, v, weakidentityhashmap, weakreference, weakreference

The Apache CXF WeakIdentityHashMap.java source code

/**
 * 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.
 */
package org.apache.cxf.common.util;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;


/**
 * Implements a combination of WeakHashMap and IdentityHashMap.
 * Useful for caches that need to key off of a == comparison
 * instead of a .equals.
 * 
 * <b>
 * This class is not a general-purpose Map implementation! While
 * this class implements the Map interface, it intentionally violates
 * Map's general contract, which mandates the use of the equals method
 * when comparing objects. This class is designed for use only in the
 * rare cases wherein reference-equality semantics are required.
 * 
 * Note that this implementation is not synchronized.
 * </b>
 */
public class WeakIdentityHashMap<K, V> implements Map {
    private final ReferenceQueue<K> queue = new ReferenceQueue();
    private Map<IdentityWeakReference, V> backingStore = new HashMap();


    public WeakIdentityHashMap() {
    }


    public void clear() {
        backingStore.clear();
        reap();
    }

    public boolean containsKey(Object key) {
        reap();
        return backingStore.containsKey(new IdentityWeakReference(key));
    }

    public boolean containsValue(Object value)  {
        reap();
        return backingStore.containsValue(value);
    }

    public Set<Map.Entry entrySet() {
        reap();
        Set<Map.Entry ret = new HashSet>();
        for (Map.Entry<IdentityWeakReference, V> ref : backingStore.entrySet()) {
            final K key = ref.getKey().get();
            final V value = ref.getValue();
            Map.Entry<K, V> entry = new Map.Entry() {
                public K getKey() {
                    return key;
                }
                public V getValue() {
                    return value;
                }
                public V setValue(V value) {
                    throw new UnsupportedOperationException();
                }
            };
            ret.add(entry);
        }
        return Collections.unmodifiableSet(ret);
    }
    public Set<K> keySet() {
        reap();
        Set<K> ret = new HashSet();
        for (IdentityWeakReference ref : backingStore.keySet()) {
            ret.add(ref.get());
        }
        return Collections.unmodifiableSet(ret);
    }

    public boolean equals(Object o) {
        if (!(o instanceof WeakIdentityHashMap)) {
            return false;
        }
        return backingStore.equals(((WeakIdentityHashMap)o).backingStore);
    }

    public V get(Object key) {
        reap();
        return backingStore.get(new IdentityWeakReference(key));
    }
    public V put(K key, V value) {
        reap();
        return backingStore.put(new IdentityWeakReference(key), value);
    }

    public int hashCode() {
        reap();
        return backingStore.hashCode();
    }
    public boolean isEmpty() {
        reap();
        return backingStore.isEmpty();
    }
    public void putAll(Map t) {
        throw new UnsupportedOperationException();
    }
    public V remove(Object key) {
        reap();
        return backingStore.remove(new IdentityWeakReference(key));
    }
    public int size() {
        reap();
        return backingStore.size();
    }
    public Collection<V> values() {
        reap();
        return backingStore.values();
    }

    private synchronized void reap() {
        Reference<? extends K> zombie = queue.poll();

        while (zombie != null) {
            backingStore.remove(zombie);
            zombie = queue.poll();
        }
    }

    class IdentityWeakReference extends WeakReference<K> {
        int hash;
        
        @SuppressWarnings("unchecked")
        IdentityWeakReference(Object obj) {
            super((K)obj, queue);
            hash = System.identityHashCode(obj);
        }

        public int hashCode() {
            return hash;
        }

        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o instanceof WeakReference) {
                WeakReference ref = (WeakReference)o;
                if (this.get() == ref.get()) {
                    return true;
                }
            }
            return false;
        }
    }
}