Java time-based map/cache with expiring keys

Java time-based map/cache with expiring keys

Do any of you know of a Java Map or similar standard data store that automatically purges entries after a given timeout? This means aging, where the old expired entries ?age-out? automatically.

Preferably in an open source library that is accessible via Maven?

I know of ways to implement the functionality myself and have done it several times in the past, so I'm not asking for advice in that respect, but for pointers to a good reference implementation.

WeakReference based solutions like WeakHashMap are not an option, because my keys are likely to be non-interned strings and I want a configurable timeout that's not dependent on the garbage collector.

Ehcache is also an option I wouldn't like to rely on because it needs external configuration files. I am looking for a code-only solution.

Answer by dty for Java time-based map/cache with expiring keys

Check out Google Collections (now called Guava). It has a map which can timeout entries automatically.

Answer by Shervin Asgari for Java time-based map/cache with expiring keys

Yes. Google Collections, or Guava as it is named now has something called MapMaker which can do exactly that.

ConcurrentMap graphs = new MapMaker()     .concurrencyLevel(4)     .softKeys()     .weakValues()     .maximumSize(10000)     .expiration(10, TimeUnit.MINUTES)     .makeComputingMap(         new Function() {           public Graph apply(Key key) {             return createExpensiveGraph(key);           }         });  

Update:

As of guava 10.0 (released September 28, 2011) many of these MapMaker methods have been deprecated in favour of the new CacheBuilder:

Cache graphs = CacheBuilder.newBuilder()      .concurrencyLevel(4)      .weakKeys()      .maximumSize(10000)      .expireAfterWrite(10, TimeUnit.MINUTES)      .build(          new CacheLoader() {            public Graph load(Key key) throws AnyException {              return createExpensiveGraph(key);            }          });  

Answer by Emil for Java time-based map/cache with expiring keys

Google collections (guava) has the MapMaker in which you can set time limit(for expiration) and you can use soft or weak reference as you choose using a factory method to create instances of your choice.

Answer by dan carter for Java time-based map/cache with expiring keys

Sounds like ehcache is overkill for what you want, however note that it does not need external configuration files.

It is generally a good idea to move configuration into a declarative configuration files ( so you don't need to recompile when a new installation requires a different expiry time ), but it is not at all required, you can still configure it programmatically. http://www.ehcache.org/documentation/user-guide/configuration

Answer by zhan Dz for Java time-based map/cache with expiring keys

ExpiringMap has similar capabilities as Google Guava.

Map map = ExpiringMap.builder()    .expiration(30, TimeUnit.SECONDS)    .build();  

Answer by toby941 for Java time-based map/cache with expiring keys

you can try Expiring Map http://www.java2s.com/Code/Java/Collections-Data-Structure/ExpiringMap.htm a class from The Apache MINA Project

Answer by Guram Savinov for Java time-based map/cache with expiring keys

Apache Commons has decorator for Map to expire enties: PassiveExpiringMap It's more simple than caches from Guava.

P.S. be careful, it's not synchronized.

Answer by piero86 for Java time-based map/cache with expiring keys

You can try out my implementation of a self-expiring hash map. This implementation does not make use of threads to remove expired entries, instead it uses DelayQueue that is cleaned up at every operation automatically.

Answer by palindrom for Java time-based map/cache with expiring keys

If anybody needs a simple thing, following is a simple key-expiring set. It might be converted to a map easily.

public class CacheSet {      public static final int TIME_OUT = 86400 * 1000;        LinkedHashMap linkedHashMap = new

LinkedHashMap() { @Override protected boolean removeEldestEntry(Map.Entry eldest) { final long time = System.currentTimeMillis(); if( time - eldest.getValue().time > TIME_OUT) { Iterator i = values().iterator(); i.next(); do { i.remove(); } while( i.hasNext() && time - i.next().time > TIME_OUT ); } return false; } }; public boolean putIfNotExists(K key) { Hit value = linkedHashMap.get(key); if( value != null ) { return false; } linkedHashMap.put(key, new Hit()); return true; } private static class Hit { final long time; Hit() { this.time = System.currentTimeMillis(); } } }

Answer by anuj dhiman for Java time-based map/cache with expiring keys

Guava cache is easy to implementation.We can expires key on time base using guava cache. I have read fully post and below gives key of my study.

cache = CacheBuilder.newBuilder().refreshAfterWrite(2,TimeUnit.SECONDS).                build(new CacheLoader(){                  @Override                  public String load(String arg0) throws Exception {                      // TODO Auto-generated method stub                      return addcache(arg0);                  }                  }  

Reference : guava cache example

Answer by Paramaeleon for Java time-based map/cache with expiring keys

Typically, a cache should keep objects around some time and shall expose of them some time later. What is a good time to hold an object depends on the use case. I wanted this thing to be simple, no threads or schedulers. This approach works for me. Unlike SoftReferences, objects are guaranteed to be available some minimum amount of time. However, the do not stay around in memory until the sun turns into a red giant.

As useage example think of a slowly responding system that shall be able to check if a request has been done quite recently, and in that case not to perform the requested action twice, even if a hectic user hits the button several times. But, if the same action is requested some time later, it shall be performed again.

class Cache {      long avg, count, created, max, min;      Map map = new HashMap();        /**       * @param min   minimal time [ns] to hold an object       * @param max   maximal time [ns] to hold an object       */      Cache(long min, long max) {          created = System.nanoTime();          this.min = min;          this.max = max;          avg = (min + max) / 2;      }        boolean add(T e) {          boolean result = map.put(e, Long.valueOf(System.nanoTime())) != null;          onAccess();          return result;      }        boolean contains(Object o) {          boolean result = map.containsKey(o);          onAccess();          return result;      }        private void onAccess() {          count++;          long now = System.nanoTime();          for (Iterator> it = map.entrySet().iterator(); it.hasNext();) {              long t = it.next().getValue();              if (now > t + min && (now > t + max || now + (now - created) / count > t + avg)) {                  it.remove();              }          }      }  }  

Answer by Vivek for Java time-based map/cache with expiring keys

This is a sample implementation that i did for the same requirement and concurrency works well. Might be useful for someone.

import java.text.SimpleDateFormat;  import java.util.Date;  import java.util.Map;  import java.util.concurrent.ConcurrentHashMap;    /**   *    * @author Vivekananthan M   *   * @param    * @param    */  public class WeakConcurrentHashMap extends ConcurrentHashMap {        private static final long serialVersionUID = 1L;        private Map timeMap = new ConcurrentHashMap();      private long expiryInMillis = 1000;      private static final SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss:SSS");        public WeakConcurrentHashMap() {          initialize();      }        public WeakConcurrentHashMap(long expiryInMillis) {          this.expiryInMillis = expiryInMillis;          initialize();      }        void initialize() {          new CleanerThread().start();      }        @Override      public V put(K key, V value) {          Date date = new Date();          timeMap.put(key, date.getTime());          System.out.println("Inserting : " + sdf.format(date) + " : " + key + " : " + value);          V returnVal = super.put(key, value);          return returnVal;      }        @Override      public void putAll(Map m) {          for (K key : m.keySet()) {              put(key, m.get(key));          }      }        @Override      public V putIfAbsent(K key, V value) {          if (!containsKey(key))              return put(key, value);          else              return get(key);      }        class CleanerThread extends Thread {          @Override          public void run() {              System.out.println("Initiating Cleaner Thread..");              while (true) {                  cleanMap();                  try {                      Thread.sleep(expiryInMillis / 2);                  } catch (InterruptedException e) {                      e.printStackTrace();                  }              }          }            private void cleanMap() {              long currentTime = new Date().getTime();              for (K key : timeMap.keySet()) {                  if (currentTime > (timeMap.get(key) + expiryInMillis)) {                      V value = remove(key);                      timeMap.remove(key);                      System.out.println("Removing : " + sdf.format(new Date()) + " : " + key + " : " + value);                  }              }          }      }  }  

Cheers!!

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