ehcache API

一 ehcache API: cache技术向来都是应用的高级话题, 但今天贴的是一个关于ehcache的低级备份.参考官方文档做的一个备份. 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: //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 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 CacheManagerehcache应该在使用后关闭, 最佳实践是在code中显式调用: //Shutdown the singleton CacheManagerCacheManager.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 MBeanServerehCache 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 usedLFU －least frequently usedFIFO－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. 感叹: csdn的blog越来越烂了, 在外面编好的格式, 粘贴过来就乱了.很是深恶痛绝!