1. OSCache – OSCache is a caching solution that includes a JSP tag library and set of classes to perform fine grained dynamic caching of JSP content, servlet responses or arbitrary objects. It provides both in memory and persistent on disk caches, and can allow your site to have graceful error tolerance (eg if an error occurs like your db goes down, you can serve the cached content so people can still surf the site almost without knowing).

2. JBoss Cache – JBoss Cache still is, as it’s name suggests, a cache. It is a product designed to cache frequently accessed Java objects in order to dramatically improve the performance of applications. This makes it easy to remove data access bottlenecks – such as connecting to a database.
And unlike non-cluster-aware caches which may go out of sync when there are concurrent updates, each JBoss Cache instance is aware of remote cache updates and can either invalidate or update it’s state.

3. cache4j – cache4j is a cache for Java objects with a simple API and fast implementation. It features in-memory caching, a design for a multi-threaded environment, both synchronized and blocking implementations, a choice of eviction algorithms (LFU, LRU, FIFO), and the choice of either hard or soft references for object storage.

4. Ehcache – Ehcache is a widely used java distributed cache for general purpose caching, Java EE and light-weight containers.

It features memory and disk stores, replicate by copy and invalidate, listeners, cache loaders, cache extensions, cache exception handlers, a gzip caching servlet filter, RESTful & SOAP APIs, an implementation of JSR107 and much more…

5. Whirlycache – Whirlycache is a fast, configurable in-memory object cache for Java. It can be used, for example, to speed up a website or an application by caching objects that would otherwise have to be created by querying a database or by another expensive procedure.

BenchMarks -

6. Java Caching System – JCS is a distributed caching system written in java. It is intended to speed up applications by providing a means to manage cached data of various dynamic natures. Like any caching system, JCS is most useful for high read, low put applications. Latency times drop sharply and bottlenecks move away from the database in an effectively cached system.