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xom-interest - Re: [XOM-interest] QName flyweights

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Subject: XOM API for Processing XML with Java

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  • From: norwoods <norwoods AT gbronline.com>
  • Cc: xom-interest AT lists.ibiblio.org
  • Subject: Re: [XOM-interest] QName flyweights
  • Date: Mon, 13 Jun 2005 12:27:37 -0700

here is another attempt at a cache. this uses an LRUCache. it can return a QName object with the methods qName=QName3.newQName(name, uri); or qName=QName3.newQName(QName3.qualifyName(prefix, localName), uri);

norwood sisson
****************************
package nu.xom;

final class QName4 {
static LRUCache cache = new LRUCache(128);

static QName4 target = new QName4();

private String localName;

private String name;

private String prefix;

private String uri;

private QName4() {
}

private QName4(String name, String uri) {
this.name = name.intern();
this.uri = uri.intern();
}

public static synchronized QName4 newQName(String name, String uri) {
if (name == null) {
throw new NullPointerException();
}
target.name = name;
if (uri == null)
uri = "";
target.uri = uri;
QName4 value = (QName4) cache.get(target);
if (value == null) {
value = new QName4(name, uri);
cache.put(value, value);
}
return value;
}

public boolean equals(Object o) {
QName4 qName = (QName4) o;
if (this == qName)
return true;
return (name.equals(qName.getQualifiedName()) && (uri.equals(qName
.getNamespaceURI())));
}

public String getLocalName() {
if (localName == null)
splitQualifiedName();
return localName;
}

public String getNamespacePrefix() {
if (prefix == null)
splitQualifiedName();
return prefix;
}

public String getNamespaceURI() {
return uri;
}

public String getQualifiedName() {
return name;
}

public int hashCode() {
return uri.hashCode() ^ name.hashCode();
}

public static String qualifyName(String prefix, String localName) {
if (prefix == null || prefix == "")
return localName;
return prefix + ":" + localName;
}

private void splitQualifiedName() {
int i = name.indexOf(':');
if (i < 0) {
prefix = "".intern();
localName = name.intern();
} else {
prefix = name.substring(0, i).intern();
localName = name.substring(i + 1).intern();
}
}
}
**************************************************
package nu.xom;

import java.util.LinkedHashMap;
import java.util.Collection;
import java.util.Map;
import java.util.ArrayList;

/**
* An LRU cache, based on <code>LinkedHashMap</code>.<br>
* This cache has a fixed maximum number of elements (<code>cacheSize</code>).
* If the cache is full and another entry is added, the LRU (least recently
* used) entry is dropped.
* <p>
* This class is thread-safe. All methods of this class are synchronized. <br>
* Author: Christian d'Heureuse ( <a
* href="http://www.source-code.biz";>www.source-code.biz </a>) <br>
* License: <a href="http://www.gnu.org/licenses/lgpl.html";>LGPL </a>.
*/
public class LRUCache<K,V> {

private final float hashTableLoadFactor = 0.75f;

private LinkedHashMap<K,V> map;
private int cacheSize;

/**
* Creates a new LRU cache.
*
* @param cacheSize
* the maximum number of entries that will be kept in this cache.
*/
public LRUCache (int cacheSize) {
this.cacheSize = cacheSize;
int hashTableCapacity = (int)Math.ceil(cacheSize / hashTableLoadFactor) + 1;
map = new LinkedHashMap<K,V>(hashTableCapacity, hashTableLoadFactor, true) {
// (an anonymous inner class)
private static final long serialVersionUID = 1;
@Override protected boolean removeEldestEntry (Map.Entry<K,V> eldest) {
return size() > LRUCache.this.cacheSize; }}; }

/**
* Retrieves an entry from the cache. <br>
* The retrieved entry becomes the MRU (most recently used) entry.
*
* @param key
* the key whose associated value is to be returned.
* @return the value associated to this key, or null if no value with this
* key exists in the cache.
*/
public synchronized V get (K key) {
return map.get(key); }

/**
* Adds an entry to this cache. If the cache is full, the LRU (least
* recently used) entry is dropped.
*
* @param key
* the key with which the specified value is to be associated.
* @param value
* a value to be associated with the specified key.
*/
public synchronized void put (K key, V value) {
map.put (key,value); }

/**
* Clears the cache.
*/
public synchronized void clear() {
map.clear(); }

/**
* Returns the number of used entries in the cache.
*
* @return the number of entries currently in the cache.
*/
public synchronized int size() {
return map.size(); }

/**
* Returns a <code>Collection</code> that contains a copy of all cache
* entries.
*
* @return a <code>Collection</code> with a copy of the cache content.
*/
public synchronized Collection<Map.Entry<K,V>> getAll() {
return new ArrayList<Map.Entry<K,V>>(map.entrySet()); }
}







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