CacheManager

CacheManager supports two creation modes: singleton and instance. The two types can exist in the same JVM. However, multiple CacheManagers with the same name are not allowed to exist in the same JVM. CacheManager() constructors creating non-Singleton CacheManagers can violate this rule, causing a NullPointerException. If your code might create multiple CacheManagers of the same name in the same JVM, avoid this error by using the static CacheManager.create() methods, which always return the named (or default unnamed) CacheManager if it already exists in that JVM. If the named (or default unnamed) CacheManager does not exist, the CacheManager.create() methods create it.

For singletons, calling CacheManager.create(...) returns the existing singleton CacheManager with the configured name (if it exists) or creates the singleton based on the passed-in configuration.

To work from configuration, use the CacheManager.newInstance(...) method, which parses the passed-in configuration to either get the existing named CacheManager or create that CacheManager if it doesn't exist.

To review, the behavior of the CacheManager creation methods is as follows:

CacheManager.newInstance(Configuration configuration) – Create a new CacheManager or return the existing one named in the configuration.

CacheManager.create() – Create a new singleton CacheManager with default configuration, or return the existing singleton. This is the same as CacheManager.getInstance().

CacheManager.create(Configuration configuration) – Create a singleton CacheManager with the passed-in configuration, or return the existing singleton.

new CacheManager(Configuration configuration) – Create a new CacheManager, or throw an exception if the CacheManager named in the configuration already exists or if the parameter (configuration) is null.

Note that in instance-mode (non-singleton), where multiple CacheManagers can be created and used concurrently in the same JVM, each CacheManager requires its own configuration.

If the Caches under management use the disk store, the disk-store path specified in each CacheManager configuration should be unique. This is because when a new CacheManager is created, a check is made to ensure that no other CacheManagers are using the same disk-store path. Depending upon your persistence strategy, Ehcache will automatically resolve a disk-store path conflict, or it will let you know that you must explicitly configure the disk-store path.

If managed caches use only the memory store, there are no special considerations.

See the Javadoc for Ehcache for more information on these methods, including options for passing in configuration. For examples, see the code samples in Creating a CacheManager.