Ehcache中可以使用Cache来保存需要缓存的对像，但需要把对象封装在Element的实例里。
往Cache中添加对像：
CacheManager manager = CacheManager.newInstance("src/config/cache.xml"); manager.addCache("testCache");Cache cache = singletonManager.getCache("testCache");Element element = new Element("key", "value"); cache.put(element);
相应源码：
/** * Put an element in the cache. * * Resets the access statistics on the element, which would be the case if it has previously been * gotten from a cache, and is now being put back. * * Also notifies the CacheEventListener that: *
- *
- the element was put, but only if the Element was actually put. *
- if the element exists in the cache, that an update has occurred, even if the element would be expired * if it was requested *
null or the key is null, it is ignored as a NOOP. * @throws IllegalStateException if the cache is not {@link Status#STATUS_ALIVE} * @throws CacheException */ public final void put(Element element) throws IllegalArgumentException, IllegalStateException, CacheException { put(element, false); } Element UML类图：
构造一个Element对象很简单，Cache没有什么复杂的操作。但看似简单的put操作，它的实现是还有点复杂。
Step 1: 开发者调用Cache的put方法。
cache.put(element);
Step 2: 对应的源码
public final void put(Element element) throws IllegalArgumentException, IllegalStateException, CacheException { put(element, false); } Step 3: 默认情况下doNotNotifyCacheReplicators的值是false.暂时先不讨论集群。
private void putAll(Collection<Element> elements, boolean doNotNotifyCacheReplicators) throws IllegalArgumentException,
IllegalStateException, CacheException {
putAllInternal(elements, doNotNotifyCacheReplicators);
}
Step 4: 具体实现细节。 可以大概看一下，今天我们主要分析一下 putObserver这个变量的作用。
private void putInternal(Element element, boolean doNotNotifyCacheReplicators, boolean useCacheWriter) { putObserver.begin(); if (useCacheWriter) { initialiseCacheWriterManager(true); } checkStatus(); if (disabled) { putObserver.end(PutOutcome.IGNORED); return; } if (element == null) { if (doNotNotifyCacheReplicators) { LOG.debug("Element from replicated put is null. This happens because the element is a SoftReference" + " and it has been collected. Increase heap memory on the JVM or set -Xms to be the same as " + "-Xmx to avoid this problem."); } putObserver.end(PutOutcome.IGNORED); return; } if (element.getObjectKey() == null) { putObserver.end(PutOutcome.IGNORED); return; } element.resetAccessStatistics(); applyDefaultsToElementWithoutLifespanSet(element); backOffIfDiskSpoolFull(); element.updateUpdateStatistics(); boolean elementExists = false; if (useCacheWriter) { boolean notifyListeners = true; try { elementExists = !compoundStore.putWithWriter(element, cacheWriterManager); } catch (StoreUpdateException e) { elementExists = e.isUpdate(); notifyListeners = configuration.getCacheWriterConfiguration().getNotifyListenersOnException(); RuntimeException cause = e.getCause(); if (cause instanceof CacheWriterManagerException) { throw ((CacheWriterManagerException)cause).getCause(); } throw cause; } finally { if (notifyListeners) { notifyPutInternalListeners(element, doNotNotifyCacheReplicators, elementExists); } } } else { elementExists = !compoundStore.put(element); notifyPutInternalListeners(element, doNotNotifyCacheReplicators, elementExists); }
putObserver，只看名字，第一反应就知道，这也许是一个观察者。Right!
private final OperationObserverputObserver = operation(PutOutcome.class).named("put").of(this).tag("cache").build();
附上相关调用的UML类图，方便大家理解。
Cache类依赖StatisticBuilder的operation()方法，通过StatisticsManager来创建GeneralOperationStatistic类的一个实例。此实例实现了OperationObserver接口的begin()和end()方法。
putObserver.begin();
注：个人觉得这个地方的代码其实是运行不到的，因为它的addDerivedStatistic方法也没有被调用到。或者是我疏忽了哪个地方，还请知情人士贡献一下。get的被用到了，下节我会详细介绍。
putObserver.end(elementExists ? PutOutcome.UPDATED : PutOutcome.ADDED);
对应的操作：
注： increment()是org.terracotta.statistics.jsr166e.LongAdder类下面基于CAS原理实现的一个线程安全的自增方法。感兴趣的朋友可以reference这个link:
从我们的调查结果中可以看出，putObserver主要目的是统计put操作时ADDED,UPDATED,IGNORED的个数。 虽然结果很简单，但更多的是让我们知道了它的设计理念以及思想。虽然实现起来很复杂，但代码看起来还是那么的简洁。