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tasks/astrid/common-src/com/todoroo/andlib/utility/SoftHashMap.java

122 lines
3.6 KiB
Java

package com.todoroo.andlib.utility;
import java.io.Serializable;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
/**
* SoftHashMap from javaspecialists.eu Issue 98
* <http://www.javaspecialists.eu/archive/Issue098.html>
*
* @param <K>
* @param <V>
*/
public class SoftHashMap<K, V> extends AbstractMap<K, V> implements
Serializable {
private static final long serialVersionUID = -3796460667941300642L;
/** The internal HashMap that will hold the SoftReference. */
private final Map<K, SoftReference<V>> hash = new HashMap<K, SoftReference<V>>();
private final Map<SoftReference<V>, K> reverseLookup = new HashMap<SoftReference<V>, K>();
/** Reference queue for cleared SoftReference objects. */
protected final ReferenceQueue<V> queue = new ReferenceQueue<V>();
@Override
public V get(Object key) {
expungeStaleEntries();
V result = null;
// We get the SoftReference represented by that key
SoftReference<V> soft_ref = hash.get(key);
if (soft_ref != null) {
// From the SoftReference we get the value, which can be
// null if it has been garbage collected
result = soft_ref.get();
if (result == null) {
// If the value has been garbage collected, remove the
// entry from the HashMap.
hash.remove(key);
reverseLookup.remove(soft_ref);
}
}
return result;
}
private void expungeStaleEntries() {
Reference<? extends V> sv;
while ((sv = queue.poll()) != null) {
hash.remove(reverseLookup.remove(sv));
}
}
@Override
public V put(K key, V value) {
expungeStaleEntries();
SoftReference<V> soft_ref = new SoftReference<V>(value, queue);
reverseLookup.put(soft_ref, key);
SoftReference<V> result = hash.put(key, soft_ref);
if (result == null)
return null;
reverseLookup.remove(result);
return result.get();
}
@Override
public V remove(Object key) {
expungeStaleEntries();
SoftReference<V> result = hash.remove(key);
if (result == null)
return null;
return result.get();
}
@Override
public void clear() {
hash.clear();
reverseLookup.clear();
}
@Override
public int size() {
expungeStaleEntries();
return hash.size();
}
/**
* Returns a copy of the key/values in the map at the point of calling.
* However, setValue still sets the value in the actual SoftHashMap.
*/
@Override
public Set<Entry<K, V>> entrySet() {
expungeStaleEntries();
Set<Entry<K, V>> result = new LinkedHashSet<Entry<K, V>>();
for (final Entry<K, SoftReference<V>> entry : hash.entrySet()) {
final V value = entry.getValue().get();
if (value != null) {
result.add(new Entry<K, V>() {
public K getKey() {
return entry.getKey();
}
public V getValue() {
return value;
}
public V setValue(V v) {
entry.setValue(new SoftReference<V>(v, queue));
return value;
}
});
}
}
return result;
}
}