ehcache常用API(http://blog.csdn.net/lcllcl987/archive/2008/06/11/2536407.aspx)

cache技术在应用中向来属于高级话题, 但今天却贴一个ehcache的低级备份.参考其官方文档整理. 一 ehcache API:

1: Using the CacheManager

1.1所有ehcache的使用, 都是从 CacheManager. 开始的. 有多种方法创建CacheManager实例:

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1. //Create a singleton CacheManager using defaults, then list caches.   
2.   
3. CacheManager.getInstance()  

//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();

如果需要从指定配置文件创建 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 手动创建一个cache, 而不是通过配置文件: //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);    }   手动移除一个cache: //Remove cache called sampleCache1 CacheManager singletonManager = CacheManager.create(); singletonManager.removeCache("sampleCache1");

1.3 Shutdown the CacheManager ehcache应该在使用后关闭, 最佳实践是在code中显式调用: //Shutdown the singleton CacheManager CacheManager.getInstance().shutdown();

 

2 Using Caches 比如我有这样一个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 获得该cache的引用:   String cacheName = "sampleCache1";   CacheManager manager = new CacheManager("src/ehcache1.xml");   Cache cache = manager.getCache(cacheName);

2.2 Performing CRUD operations 下面的代码演示了ehcache的增删改查:  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"));  } 备注: 持久化到硬盘的路径由虚拟机参数"java.io.tmpdir"决定. 例如, 在windows中, 会在此路径下 C:/Documents and Settings/li/Local Settings/Temp 在linux中, 通常会在: /tmp 下

2.4  Obtaining Cache Sizes 以下代码演示如何获得cache个数:  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); 把该程序打包, 然后: java -Dcom.sun.management.jmxremote -jar 程序名.jar

再到javahome/bin中运行jconsole.exe, 便可监控cache.

4. 用户可以自定义处理cacheEventHandler, 处理诸如元素放入cache的各种事件(放入,移除,过期等事件) 只需三步: 4.1 在cache配置中, 增加cacheEventListenerFactory节点.  <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: 编写EventFactory, 继承CacheEventListenerFactory: public class EventFactory extends CacheEventListenerFactory  {  @Override  public CacheEventListener createCacheEventListener(Properties properties)  {   // TODO Auto-generated method stub   return new CacheEvent();  }

}

4.3  编写 class: CacheEvent, 实现 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);     } }

现在可以编写测试代码:  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));  }    根据配置, 该缓存对象生命期只有2分钟, 在Thread.sleep(10000)期间, 该缓存元素将过期被销毁, 在销毁前, 触发notifyElementExpired事件.   二 Ehcache配置文件  以如下配置为例说明:   <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数量。如果放入cache中的元素超过这个数值，有两种情况： 1、若overflowToDisk的属性值为true，会将cache中多出的元素放入磁盘文件中。 2、若overflowToDisk的属性值为false，会根据memoryStoreEvictionPolicy的策略替换cache中原有的元素。 eternal ：是否永驻内存。如果值是true，cache中的元素将一直保存在内存中，不会因为时间超时而丢失，所以在这个值为true的时候， timeToIdleSeconds和timeToLiveSeconds两个属性的值就不起作用了。  timeToIdleSeconds ：访问这个cache中元素的最大间隔时间。如果超过这个时间没有访问这个cache中的某个元素，那么这个元素将被从cache中清除。 timeToLiveSeconds : cache中元素的生存时间。意思是从cache中的某个元素从创建到消亡的时间，从创建开始计时，当超过这个时间，这个元素将被从cache中清除。 overflowToDisk ：溢出是否写入磁盘。系统会根据标签<diskStore path="java.io.tmpdir"/> 中path的值查找对应的属性值，如果系统的java.io.tmpdir的值是 D:/temp，写入磁盘的文件就会放在这个文件夹下。文件的名称是cache的名称，后缀名的data。如：CACHE_FUNC.data。 diskExpiryThreadIntervalSeconds  ：磁盘缓存的清理线程运行间隔. memoryStoreEvictionPolicy ：内存存储与释放策略。有三个值： LRU －least recently used LFU －least frequently used FIFO－first in first out, the oldest element by creation time diskPersistent ： 是否持久化磁盘缓存。当这个属性的值为true时，系统在初始化的时候会在磁盘中查找文件名为cache名称，后缀名为index的的文件，如CACHE_FUNC.index 。这个文件中存放了已经持久化在磁盘中的cache的index，找到后把cache加载到内存。要想把cache真正持久化到磁盘，写程序时必须注意，在是用net.sf.ehcache.Cache的void put (Element element)方法后要使用void flush()方法。  更多说明可看ehcache自带的ehcache.xml的注释说明.