ehcache常用API整理

鑑於csdn的blog的不穩定, 及混亂的編輯器, 和無上傳功能, 遂決定徹底投誠javaeye的blog.

數月前整理的一個東西, 作爲cache的掃盲文檔.參考了它的官方文檔.

對ehcache感興趣的兄臺可以參考.

附件爲eclipse項目, 直接導入, 運行test目錄下的junit testcase, 可一目瞭然.
一 ehcache API:

1: Using the CacheManager

1.1所有ehcache的使用, 都是從 CacheManager. 開始的.
有多種方法創建CacheManager實例:

//Create a singleton CacheManager using defaults, then list caches.
CacheManager.getInstance()

或者:

//Create a CacheManager instance using defaults, then list caches.
CacheManager manager = new CacheManager();
String[] cacheNames = manager.getCacheNames();

如果需要從指定配置文件創建 CacheManager:

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();

1.2 Adding and Removing Caches Programmatically
手動創建一個cache, 而不是通過配置文件:

//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");

或者:

//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.
    public void testCreatCacheByProgram()
    {
        CacheManager singletonManager = CacheManager.create();
        Cache memoryOnlyCache = new Cache("testCache", 5000, false, false, 5, 2);
        singletonManager.addCache(memoryOnlyCache);
        Cache testCache = singletonManager.getCache("testCache");
        assertNotNull(testCache);       
    }

手動移除一個cache:

//Remove cache called sampleCache1
CacheManager singletonManager = CacheManager.create();
singletonManager.removeCache("sampleCache1");

1.3 Shutdown the CacheManager
ehcache應該在使用後關閉, 最佳實踐是在code中顯式調用:

//Shutdown the singleton CacheManager
CacheManager.getInstance().shutdown();

2 Using Caches
比如我有這樣一個cache:

    <cache name="sampleCache1" maxElementsInMemory="10000"
        maxElementsOnDisk="1000" eternal="false" overflowToDisk="true"
        diskSpoolBufferSizeMB="20" timeToIdleSeconds="300"
        timeToLiveSeconds="600" memoryStoreEvictionPolicy="LFU" />

2.1 Obtaining a reference to a Cache
獲得該cache的引用:

        String cacheName = "sampleCache1";
        CacheManager manager = new CacheManager("src/ehcache1.xml");
        Cache cache = manager.getCache(cacheName);

2.2 Performing CRUD operations
下面的代碼演示了ehcache的增刪改查:

    public void testCRUD()
    {
        String cacheName = "sampleCache1";
        CacheManager manager = new CacheManager("src/ehcache1.xml");
        Cache cache = manager.getCache(cacheName);
        //Put an element into a cache
        Element element = new Element("key1", "value1");
        cache.put(element);
        //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".
        element = cache.get("key1");
        Serializable value = element.getValue();
        //Get a NonSerializable value from an element in a cache with a key of "key1".
        element = cache.get("key1");
        assertNotNull(element);
        Object valueObj = element.getObjectValue();
        assertNotNull(valueObj);
        //Remove an element from a cache with a key of "key1".
        assertNotNull(cache.get("key1"));
        cache.remove("key1");
        assertNull(cache.get("key1"));
       
    }

2.3 Disk Persistence on demand

//sampleCache1 has a persistent diskStore. We wish to ensure that the data //and index are written immediately.
        public void testDiskPersistence()
    {
        String cacheName = "sampleCache1";
        CacheManager manager = new CacheManager("src/ehcache1.xml");
        Cache cache = manager.getCache(cacheName);
        for (int i = 0; i < 50000; i++)
        {
            Element element = new Element("key" + i, "myvalue" + i);
            cache.put(element);
        }
        cache.flush();
        Log.debug("java.io.tmpdir = " + System.getProperty("java.io.tmpdir"));
    }

備註: 持久化到硬盤的路徑由虛擬機參數"java.io.tmpdir"決定.
例如, 在windows中, 會在此路徑下
C:\Documents and Settings\li\Local Settings\Temp
在linux中, 通常會在: /tmp 下

2.4 Obtaining Cache Sizes
以下代碼演示如何獲得cache個數:

    public void testCachesizes()
    {
        long count = 5;
        String cacheName = "sampleCache1";
        CacheManager manager = new CacheManager("src/ehcache1.xml");
        Cache cache = manager.getCache(cacheName);
        for (int i = 0; i < count; i++)
        {
            Element element = new Element("key" + i, "myvalue" + i);
            cache.put(element);
        }
        //Get the number of elements currently in the Cache.
        int elementsInCache = cache.getSize();
        assertTrue(elementsInCache == 5);
        //Cache cache = manager.getCache("sampleCache1");
        long elementsInMemory = cache.getMemoryStoreSize();
        //Get the number of elements currently in the DiskStore.
        long elementsInDiskStore = cache.getDiskStoreSize();
        assertTrue(elementsInMemory + elementsInDiskStore == count);   
    }

3: Registering CacheStatistics in an MBeanServer
ehCache 提供jmx支持:

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

把該程序打包, 然後:

java -Dcom.sun.management.jmxremote -jar 程序名.jar

再到javahome/bin中運行jconsole.exe, 便可監控cache.

4. 用戶可以自定義處理cacheEventHandler, 處理諸如元素放入cache的各種事件(放入,移除,過期等事件)
只需三步:
4.1 在cache配置中, 增加cacheEventListenerFactory節點.

    <cache name="Test" maxElementsInMemory="1" eternal="false"
        overflowToDisk="true" timeToIdleSeconds="1" timeToLiveSeconds="2"
        diskPersistent="false" diskExpiryThreadIntervalSeconds="1"
        memoryStoreEvictionPolicy="LFU">
        <cacheEventListenerFactory class="co.ehcache.EventFactory" />
    </cache>

4.2: 編寫EventFactory, 繼承CacheEventListenerFactory:

public class EventFactory extends CacheEventListenerFactory 
{
    @Override
    public CacheEventListener createCacheEventListener(Properties properties)
    {
        // TODO Auto-generated method stub
        return new CacheEvent();
    }

}

4.3 編寫 class: CacheEvent, 實現 CacheEventListener 接口:

public class CacheEvent implements CacheEventListener 
{

    public void dispose()
    {
        log("in dispose");
    }

    public void notifyElementEvicted(Ehcache cache, Element element)
    {
        // TODO Auto-generated method stub
        log("in notifyElementEvicted" + element);
    }

    public void notifyElementExpired(Ehcache cache, Element element)
    {
        // TODO Auto-generated method stub
        log("in notifyElementExpired" + element);
    }

    public void notifyElementPut(Ehcache cache, Element element) throws CacheException
    {
        // TODO Auto-generated method stub
        log("in notifyElementPut" + element);
    }

    public void notifyElementRemoved(Ehcache cache, Element element) throws CacheException
    {
        // TODO Auto-generated method stub
        log("in notifyElementRemoved" + element);
    }

    public void notifyElementUpdated(Ehcache cache, Element element) throws CacheException
    {
        // TODO Auto-generated method stub
        log("in notifyElementUpdated" + element);
    }

    public void notifyRemoveAll(Ehcache cache)
    {
        // TODO Auto-generated method stub
        log("in notifyRemoveAll");
    }
   
    public Object clone() throws CloneNotSupportedException
    {
        return super.clone();
    }   
   
    private void log(String s)
    {
        Log.debug(s);
    }
}

現在可以編寫測試代碼:

    public void testEventListener()
    {
        String key = "person";
        Person person = new Person("lcl", 100);
        MyCacheManager.getInstance().put("Test", key, person);
        Person p = (Person) MyCacheManager.getInstance().get("Test", key);

        try
        {
            Thread.sleep(10000);
        }
        catch (InterruptedException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        assertNull(MyCacheManager.getInstance().get("Test", key));
    }

    根據配置, 該緩存對象生命期只有2分鐘, 在Thread.sleep(10000)期間, 該緩存元素將過期被銷燬, 在銷燬前, 觸發notifyElementExpired事件.

二 Ehcache配置文件
以如下配置爲例說明:

<cache name="CACHE_FUNC" 
maxElementsInMemory="2" 
eternal="false" 
timeToIdleSeconds="10" 
timeToLiveSeconds="20"
overflowToDisk="true" 
diskPersistent="true" 
diskExpiryThreadIntervalSeconds="120"  />

maxElementsInMemory ：cache 中最多可以存放的元素的數量。如果放入cache中的元素超過這個數值，有兩種情況：
1. 若overflowToDisk的屬性值爲true，會將cache中多出的元素放入磁盤文件中。
2. 若overflowToDisk的屬性值爲false，會根據memoryStoreEvictionPolicy的策略替換cache中原有的元素。

eternal ：是否永駐內存。如果值是true，cache中的元素將一直保存在內存中，不會因爲時間超時而丟失，所以在這個值爲true的時候，timeToIdleSeconds和timeToLiveSeconds兩個屬性的值就不起作用了。

3. timeToIdleSeconds ：訪問這個cache中元素的最大間隔時間。如果超過這個時間沒有訪問這個cache中的某個元素，那麼這個元素將被從cache中清除。

4. timeToLiveSeconds : cache中元素的生存時間。意思是從cache中的某個元素從創建到消亡的時間，從創建開始計時，當超過這個時間，這個元素將被從cache中清除。

5. overflowToDisk ：溢出是否寫入磁盤。系統會根據標籤<diskStore path="java.io.tmpdir"/> 中path的值查找對應的屬性值，如果系統的java.io.tmpdir的值是 D:\temp，寫入磁盤的文件就會放在這個文件夾下。文件的名稱是cache的名稱，後綴名的data。如：CACHE_FUNC.data。

6. diskExpiryThreadIntervalSeconds ：磁盤緩存的清理線程運行間隔.

7. memoryStoreEvictionPolicy ：內存存儲與釋放策略。有三個值：
LRU －least recently used
LFU －least frequently used
FIFO－first in first out, the oldest element by creation time

diskPersistent ：是否持久化磁盤緩存。當這個屬性的值爲true時，系統在初始化的時候會在磁盤中查找文件名爲cache名稱，後綴名爲index的的文件，如CACHE_FUNC.index 。這個文件中存放了已經持久化在磁盤中的cache的index，找到後把cache加載到內存。要想把cache真正持久化到磁盤，寫程序時必須注意，在是用net.sf.ehcache.Cache的void put (Element element)方法後要使用void flush()方法。
更多說明可看ehcache自帶的ehcache.xml的註釋說明.

ehcache常用API整理

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