Monday, December 30, 2013

Ehcache: Java's Most Widely-Used Cache

Ehcache is an open source, standards-based cache for boosting performance, offloading your database, and simplifying scalability. It's the most widely-used Java-based cache because it's robust, proven, and full-featured. Ehcache scales from in-process, with one or more nodes, all the way to mixed in-process/out-of-process configurations with terabyte-sized caches.
Terracotta actively develops, maintains, and supports Ehcache as a professional open source project available under an Apache 2 license. In addition to the open source Ehcache edition, Terracotta offers BigMemory for enterprise-grade in-memory data management with high availability, worldwide 24x7 professional support, consulting, and training services.
For applications requiring a coherent distributed cache, use Terracotta BigMemory Max, which is available in both free and full versions. (Terracotta no longer actively updates the open-source version of Terracotta Server Array, also known as Terracotta. However, you can still download the latest open-source version of Terrcotta Server Array.)

Code Samples


The Code Samples page contains examples that will help you get started with Ehcache.
If you have suggestions or ideas for more code samples, please tell us about them using the forums or mailing list.

Using the CacheManager

All usages of Ehcache start with the creation of a CacheManager. See Key Classes and Methods for details on how to create CacheManagers.

Singleton versus Instance

Create a singleton CacheManager using defaults, then list caches.
String[] cacheNames = CacheManager.getInstance().getCacheNames();
Create a CacheManager instance using defaults, then list caches.
String[] cacheNames = manager.getCacheNames();
Create two CacheManagers, each with a different configuration, and list the caches in each.
CacheManager manager1 = CacheManager.newInstance("src/config/ehcache1.xml");
CacheManager manager2 = CacheManager.newInstance("src/config/ehcache2.xml");
String[] cacheNamesForManager1 = manager1.getCacheNames();
String[] cacheNamesForManager2 = manager2.getCacheNames();

Ways of loading Cache Configuration

When the CacheManager is created it creates caches found in the configuration. Create a CacheManager using defaults. Ehcache will look for ehcache.xml in the classpath.
CacheManager manager = CacheManager.newInstance();
Create a CacheManager specifying the path of a configuration file.
CacheManager manager = CacheManager.newInstance("src/config/ehcache.xml");
Create a CacheManager from a configuration resource in the classpath.
URL url = getClass().getResource("/anotherconfigurationname.xml");
CacheManager manager = CacheManager.newInstance(url);
Create a CacheManager from a configuration in an InputStream.
InputStream fis = new FileInputStream(new File("src/config/ehcache.xml").getAbsolutePath());
try {
  CacheManager manager = CacheManager.newInstance(fis);
} finally {

Adding and Removing Caches Programmatically

You are not just stuck with the caches that were placed in the configuration. You can create and remove them programmatically. Add a cache using defaults, then use it. The following example creates a cache called , which will be configured using defaultCache from the configuration.
CacheManager singletonManager = CacheManager.create();
Cache test = singletonManager.getCache("testCache");
Create a Cache and add it to the CacheManager, then use it. Note that Caches are not usable until they have been added to a CacheManager.
CacheManager singletonManager = CacheManager.create();
Cache memoryOnlyCache = new Cache("testCache", 5000, false, false, 5, 2);
Cache test = singletonManager.getCache("testCache");
See the cache constructor for the full parameters for a new Cache.
Remove cache called sampleCache1:
CacheManager singletonManager = CacheManager.create();

Shutdown the CacheManager

Ehcache should be shutdown after use. It does have a shutdown hook, but it is best practice to shut it down in your code.
Shutdown the singleton CacheManager:
Shutdown a CacheManager instance, assuming you have a reference to the CacheManager called :
See the CacheManagerTest for more examples.

Creating Caches Programmatically

Creating a new cache from defaults

A new cache with a given name can be created from defaults very simply:

Creating a new cache with custom parameters

The configuration for a Cache can be specified programmatically as an argument to the Cache constructor:
public Cache(CacheConfiguration cacheConfiguration) {
Here is an example which creates a cache called "testCache."
//Create a singleton CacheManager using defaults
CacheManager manager = CacheManager.create();

//Create a Cache specifying its configuration.
Cache testCache = new Cache(
  new CacheConfiguration("testCache", maxEntriesLocalHeap)
    .persistence(new PersistenceConfiguration().strategy(Strategy.LOCALTEMPSWAP)));
Once the cache is created, add it to the list of caches managed by the CacheManager:
The cache is not usable until it has been added.

Using Caches

All of these examples refer to , which is a reference to a CacheManager, which has a cache in it called .

Obtaining a reference to a Cache {#Obtaining a reference to a Cache}

Obtain a Cache called "sampleCache1", which has been preconfigured in the configuration file
Cache cache = manager.getCache("sampleCache1");

Performing CRUD operations

Put an element into a cache
Cache cache = manager.getCache("sampleCache1");
Element element = new Element("key1", "value1");
Update an element in a cache. Even though cache.put() is used, Ehcache knows there is an existing element, and considers the put an update for the purpose of notifying cache listeners.
Cache cache = manager.getCache("sampleCache1");
cache.put(new Element("key1", "value1"));
//This updates the entry for "key1"
cache.put(new Element("key1", "value2"));
Get a Serializable value from an element in a cache with a key of "key1".
Cache cache = manager.getCache("sampleCache1");
Element element = cache.get("key1");
Serializable value = element.getValue();
Get a NonSerializable value from an element in a cache with a key of "key1".
Cache cache = manager.getCache("sampleCache1");
Element element = cache.get("key1");
Object value = element.getObjectValue();
Remove an element from a cache with a key of "key1".
Cache cache = manager.getCache("sampleCache1");

Obtaining Cache Sizes

Get the number of elements currently in the Cache.
Cache cache = manager.getCache("sampleCache1");
int elementsInMemory = cache.getSize();
Get the number of elements currently in the MemoryStore.
Cache cache = manager.getCache("sampleCache1");
long elementsInMemory = cache.getMemoryStoreSize();
Get the number of elements currently in the DiskStore.
Cache cache = manager.getCache("sampleCache1");
long elementsInMemory = cache.getDiskStoreSize();

Obtaining Statistics of Cache Hits and Misses

These methods are useful for tuning cache configurations. Get the number of times requested items were found in the cache (cache hits).
Cache cache = manager.getCache("sampleCache1");
int hits = cache.getHitCount();
Get the number of times requested items were found in the MemoryStore of the cache.
Cache cache = manager.getCache("sampleCache1");
int hits = cache.getMemoryStoreHitCount();
Get the number of times requested items were found in the DiskStore of the cache.
Cache cache = manager.getCache("sampleCache1");
int hits = cache.getDiskStoreCount();
Get the number of times requested items were not found in the cache (cache misses).
Cache cache = manager.getCache("sampleCache1");
int hits = cache.getMissCountNotFound();
Get the number of times requested items were not found in the cache due to expiry of the elements.
Cache cache = manager.getCache("sampleCache1");
int hits = cache.getMissCountExpired();
These are just the most commonly used methods. See CacheTest for more examples. See Cache for the full API.

Dynamically Modifying Cache Configurations

This example shows how to dynamically modify the cache configuration of an already running cache:
Cache cache = manager.getCache("sampleCache");
CacheConfiguration config = cache.getCacheConfiguration();
Dynamic cache configurations can also be frozen to prevent future changes:
Cache cache = manager.getCache("sampleCache");


A cache will automatically participate in the ongoing UserTransaction when configured in transactionalMode XA.
Note that XA Transactional caches are supported only for local Ehcache, BigMemory Go, and BigMemory Max. Replicated Ehcache architectures such as RMI, JMS, or JGroups are not supported as there is no locking in those architectures.

Cache Statistics and Monitoring

Registering CacheStatistics in an MBeanServer

This example shows how to register CacheStatistics in the JDK1.5 platform MBeanServer, which works with the JConsole management agent.
CacheManager manager = CacheManager.newInstance();
MBeanServer mBeanServer = ManagementFactory.getPlatformMBeanServer();
ManagementService.registerMBeans(manager, mBeanServer, false, false, false, true);

More examples

JCache Examples

See the examples in JCache.

Cache Server Examples

See the examples in Cache Server.

Browse the JUnit Tests

Ehcache comes with a comprehensive JUnit test suite, which not only tests the code, but shows you how to use ehcache. A link to browsable unit test source code for the major Ehcache classes is given per section. The unit tests are also in the in the Ehcache tarball.


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