src/main/java/org/apache/pdfbox/jbig2/util/cache/SoftReferenceCache.java

/**
 * 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.pdfbox.jbig2.util.cache;

import java.lang.ref.SoftReference;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;

public class SoftReferenceCache implements Cache
{
    private final Map<Object, SoftReference<?>> cache =
            Collections.synchronizedMap(new WeakHashMap<Object, SoftReference<?>>());

    @Override
    public Object put(Object key, Object value, int sizeEstimate)
    {
        SoftReference<Object> softReference = new SoftReference<Object>(value);
        SoftReference<?> oldValue = cache.put(key, softReference);
        return getValueNullSafe(oldValue);
    }

    @Override
    public Object get(Object key)
    {
        SoftReference<?> softReference = cache.get(key);
        return getValueNullSafe(softReference);
    }

    @Override
    public void clear()
    {
        cache.clear();
    }

    @Override
    public Object remove(Object key)
    {
        SoftReference<?> removedObj = cache.remove(key);
        return getValueNullSafe(removedObj);
    }

    private Object getValueNullSafe(SoftReference<?> softReference)
    {
        return softReference == null ? null : softReference.get();
    }
}