Code Samples

This page shows some of the more common code samples to get you started. Code samples for each feature are in the relevant chapters.

Using the CacheManager

All usages of ehcache start with the creation of a CacheManager.

Singleton versus Instance

As of ehcache-1.2, ehcache CacheManagers can be created as either singletons (use the create factory method) or instances (use new).

Create a singleton CacheManager using defaults, then list caches.

CacheManager.create();
String[] cacheNames = CacheManager.getInstance().getCacheNames();

Create a CacheManager instance using defaults, then list caches.

 CacheManager manager = new CacheManager();
 String[] cacheNames = manager.getCacheNames();

Create two CacheManagers, each with a different configuration, and list the caches in each.

 CacheManager manager1 = new CacheManager("src/config/ehcache1.xml");
 CacheManager manager2 = new CacheManager("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 = new CacheManager();

Create a CacheManager specifying the path of a configuration file.

CacheManager manager = new CacheManager("src/config/ehcache.xml");

Create a CacheManager from a configuration resource in the classpath.

URL url = getClass().getResource("/anotherconfigurationname.xml");
CacheManager manager = new CacheManager(url);

Create a CacheManager from a configuration in an InputStream.

InputStream fis = new FileInputStream(new File("src/config/ehcache.xml").getAbsolutePath());
try {
    CacheManager manager = new CacheManager(fis);
} finally {
    fis.close();
}

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 testCache , which will be configured using defaultCache from the configuration.

CacheManager singletonManager = CacheManager.create();
singletonManager.addCache("testCache");
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);
manager.addCache(memoryOnlyCache);
Cache test = singletonManager.getCache("testCache");

See Cache#Cache(...) for the full parameters for a new Cache:

Remove cache called sampleCache1

CacheManager singletonManager = CacheManager.create();
singletonManager.removeCache("sampleCache1");

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

CacheManager.getInstance().shutdown();

Shutdown a CacheManager instance, assuming you have a reference to the CacheManager called manager 

manager.shutdown();

See the CacheManagerTest for more examples.

Using Caches

All of these examples refer to manager , which is a reference to a CacheManager, which has a cache in it called sampleCache1 .

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");
cache.put(element);

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");
Element element = new Element("key1", "value1"
cache.remove("key1");

Disk Persistence on demand

sampleCache1 has a persistent diskStore. We wish to ensure that the data and index are written immediately.

Cache cache = manager.getCache("sampleCache1");
cache.flush();

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. i.e. 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. i.e. 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.

Creating a new cache from defaults

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

manager.addCache("cache name");

Creating a new cache with custom parameters

The configuration for a Cache can be specified programmatically in the Cache constructor:

public Cache(
    String name,
    int maxElementsInMemory,
    MemoryStoreEvictionPolicy memoryStoreEvictionPolicy,
    boolean overflowToDisk,
    boolean eternal,
    long timeToLiveSeconds,
    long timeToIdleSeconds,
    boolean diskPersistent,
    long diskExpiryThreadIntervalSeconds) {
    ...
   }

Here is an example which creates a cache called test.

   //Create a CacheManager using defaults
   CacheManager manager = CacheManager.create();

   //Create a Cache specifying its configuration.

   Cache testCache = new Cache("test", maxElements,
   MemoryStoreEvictionPolicy.LFU, true, false, 60, 30, false, 0);
   manager.addCache(cache);

Once the cache is created, add it to the list of caches managed by the CacheManager:

     manager.addCache(testCache);

The cache is not usable until it has been added.

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 = new CacheManager();
    MBeanServer mBeanServer = ManagementFactory.getPlatformMBeanServer();
    ManagementService.registerMBeans(manager, mBeanServer, false, false, false, true);

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 src.zip in the ehcache tarball.