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")); } 2.3Disk 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 stublog("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 blocke.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!