Looking for simple Java in-memory cache

Question

I m looking for a simple Java in-memory cache that has good concurrency  so LinkedHashMap isn t good enough   and which can be serialized to disk periodically   One feature I need  but which has proved hard to find  is a way to  peek  at an object   By this I mean retrieve an object from the cache without causing the cache to hold on to the object any longer than it otherwise would have   Update  An additional requirement I neglected to mention is that I need to be able to modify the cached objects  they contain float arrays  in-place   Can anyone provide any recommendations

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Ehcache is a pretty good solution for this and has a way to peek  getQuiet   is the method  such that it doesn t update the idle timestamp   Internally  Ehcache is implemented with a set of maps  kind of like ConcurrentHashMap  so it has similar kinds of concurrency benefits

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If you re needing something simple  would this fit the bill   Map lt K  V gt  myCache   Collections synchronizedMap new WeakHashMap lt K  V gt        It wont save to disk  but you said you wanted simple     Links    Collections synchronizedMap WeakHashMap    As Adam commented  synchronising a map has a performance hit  Not saying the idea doesn t have hairs on it  but would suffice as a quick and dirty solution

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You can easily use imcache  A sample code is below   void example        Cache lt Integer Integer gt  cache   CacheBuilder heapCache        cacheLoader new CacheLoader lt Integer  Integer gt              public Integer load Integer key                return null                   capacity 10000  build

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Since this question was originally asked  Google s Guava library now includes a powerful and flexible cache   I would recommend using this

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Another option for an in-memory java cache is cache2k   The in-memory performance is superior to EHCache and google guava  see the cache2k benchmarks page    The usage pattern is similar to other caches  Here is an example   Cache lt String String gt  cache   new Cache2kBuilder lt String  String gt          expireAfterWrite 5  TimeUnit MINUTES        expire refresh after 5 minutes    resilienceDuration 30  TimeUnit SECONDS     cope with at most 30 seconds                                              outage before propagating                                               exceptions    refreshAhead true                           keep fresh when expiring    loader new CacheLoader lt String  String gt           Override     public String load final String key  throws Exception         return                     build    String val   cache peek  something    cache put  something    hello    val   cache get  something      If you have google guava as dependency then trying out guava cache  may be a good alternative

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Try  Cacheable from jcabi-aspects  With a single annotation you make the entire method result cacheable in memory   public class Resource      Cacheable lifetime   5  unit   TimeUnit SECONDS    public String load URL url        return url openConnection   getContent            Also  read this article  http   www yegor256 com 2014 08 03 cacheable-java-annotation html

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Try this   import java util     public class SimpleCacheManager        private static SimpleCacheManager instance      private static Object monitor   new Object        private Map lt String  Object gt  cache   Collections synchronizedMap new HashMap lt String  Object gt           private SimpleCacheManager                public void put String cacheKey  Object value            cache put cacheKey  value              public Object get String cacheKey            return cache get cacheKey              public void clear String cacheKey            cache put cacheKey  null              public void clear             cache clear               public static SimpleCacheManager getInstance             if  instance    null                synchronized  monitor                    if  instance    null                        instance   new SimpleCacheManager                                                      return instance

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How about this  https   commons apache org proper commons-jcs   updated to new address  as JCS is now in Apache Commons

User · Answer

Try Ehcache  It allows you to plug in your own caching expiry algorithms so you could control your peek functionality    You can serialize to disk  database  across a cluster etc

[java] Looking for simple Java in-memory cache

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