I want to implement some sort of lightweight caching in Java which is easily integrable in Java and should be easy to deploy with a Java application.
The cache layer will be between the application and the database layer: no database caching, no Spring, no Hibernate, no EHcache, no http caching.
We can use a file system or a nano database so that the cache can be restored so that the cache can be restored after the process restart.
I tried LRU Cache:
http://stackoverflow.com/questions/224868/easy-simple-to-use-lru-cache-in-java
http://www.programcreek.com/2013/03/leetcode-lru-cache-java/
But I am not sure how to after overflow should I save database into database (which database will be better to use for faster insert and seek of data). Or I should use File System?
Any one has better inputs to implement caching mechanism in Java?
But I am not sure how to after overflow should I save database into database(which database will be better to use for faster insert ans seek ok data) Or I should use File System?
It depends on the use case. If your cached values are very big, you can store each of it in a file and use the hash of the cache key as file name.
If you have values small in size, storing them as separate files would be a lot of overhead, so it is better to store the cached entries into one or a couple of files. To implement this you need to learn about "external indexes" and "memory management" or "free space management" (e.g. best fit, next fit and compaction strategies). This actually leads to the implementation of a tiny database, so may be use one :) Some stuff that comes to my mind: LevelDB, MapDB, LMDB, RocksDB
Keep in mind that caching operations come in concurrently from the application, so the cache may evict a value and a request to the same key may come in at the same time. Will you implement just the basic operations like Cache.get and Cache.put or also CAS-operations like Cache.putIfAbsent? Do you want to efficiently use multi core system, as they are common today?
Still, when using a tiny database, you will need to prepare for some months of engineering work.
Any one has better inputs to implement caching mechanism in Java?
You can read my blog at cruftex.net for some more input to implement lightweight and fast caching in Java.
For a cache implementation with overflow you can take a look at imcache. But imcache is not a fully-fledged generic cache, because for example CAS-operations are missing, see the Cache interface
My own high performance Java cache implementation cache2k, features CAS-operations, events, loaders&writers, expiry, etc. and it will eventually get some overflow to disk, too. However, I am not sure about the time frame... When you are interested to work in this area: contributions are welcome!