Easy, simple to use LRU cache in java

Question

I know it's simple to implement, but I want to reuse something that already exist.

Problem I want to solve is that I load configuration (from XML so I want to cache them) for different pages, roles, ... so the combination of inputs can grow quite much (but in 99% will not). To handle this 1%, I want to have some max number of items in cache...

Till know I have found org.apache.commons.collections.map.LRUMap in apache commons and it looks fine but want to check also something else. Any recommendations?

Answer 1

You can use a LinkedHashMap (Java 1.4+) :

// Create cache final int MAX_ENTRIES = 100; Map cache = new LinkedHashMap(MAX_ENTRIES+1, .75F, true) {     // This method is called just after a new entry has been added     public boolean removeEldestEntry(Map.Entry eldest) {         return size() > MAX_ENTRIES;     } };  // Add to cache Object key = "key"; cache.put(key, object);  // Get object Object o = cache.get(key); if (o == null && !cache.containsKey(key)) {     // Object not in cache. If null is not a possible value in the cache,     // the call to cache.contains(key) is not needed }  // If the cache is to be used by multiple threads, // the cache must be wrapped with code to synchronize the methods cache = (Map)Collections.synchronizedMap(cache); 

Answer 2

This is an old question, but for posterity I wanted to list ConcurrentLinkedHashMap, which is thread safe, unlike LRUMap. Usage is quite easy:

ConcurrentMap<K, V> cache = new ConcurrentLinkedHashMap.Builder<K, V>()     .maximumWeightedCapacity(1000)     .build(); 

And the documentation has some good examples, like how to make the LRU cache size-based instead of number-of-items based.