在系列三中我们介绍了可以通过配置文件或者参数传递来配置Ehcache的系统参数。但是如果我们想动态的去调整这些参数应该怎么办呢？
这是完全可行的，Cache提供了相应的方法。
Cache cache = manager.getCache("sampleCache");
CacheConfiguration config = cache.getCacheConfiguration();
config.setTimeToIdleSeconds(60);
config.setTimeToLiveSeconds(120);
config.setmaxEntriesLocalHeap(10000);
config.setmaxEntriesLocalDisk(1000000);
/**
* @param propertyName
* @param oldValue
* @param newValue
*/
public void firePropertyChange(String propertyName, Object oldValue, Object newValue) {
PropertyChangeSupport pcs;
synchronized (this) {
pcs = propertyChangeSupport;
}
if (pcs != null && (oldValue != null || newValue != null)) {
pcs.firePropertyChange(propertyName, oldValue, newValue);
}
}先让我们来回忆一下PropertyChangeSupport的具体用法。
PropertyChangeSupport类的官方文档解释：
This is a utility class that can be used by beans that support bound properties. You can use an instance of this class as a member field of your bean and delegate various work to it.关联属性，也称绑定属性。当绑定属性值发生变化时，通知所有相关的监听器。为了实现属性绑定，必须实现两个机制。
只要属性的值发生变化，该bean发送一个PropertyChange事件给所有已注册的监听器。该变化可以发生在调用set方法时，或者程序的用户做出某种动作时。
为了使感兴趣的监听器能够进行注册，bean必须实现以下两个方法：
void addPropertyChangeListener(PropertyChangeListener listener);
void removePropertyChangeListener(PropertyChangeListener listener);通过java.bean包下的PropertyChangeSupport类来管理监听器。要使用这个类，bean必须有一个此类的数据域。
private final PropertyChangeSupport propertyChangeSupport = new PropertyChangeSupport(this); /**
* @param listener
*/
public synchronized void addPropertyChangeListener(PropertyChangeListener listener) {
if (listener != null && propertyChangeSupport != null) {
propertyChangeSupport.removePropertyChangeListener(listener);
propertyChangeSupport.addPropertyChangeListener(listener);
}
}
/**
* @param listener
*/
public synchronized void removePropertyChangeListener(PropertyChangeListener listener) {
if (listener != null && propertyChangeSupport != null) {
propertyChangeSupport.removePropertyChangeListener(listener);
}
}当bean的属性发生变化时，使用PropertyChangeSupport对象的firePropertyChange方法，它会将一个事件发送给所有已经注册的监听器。该方法有三个参数：属性的名字、旧的值以及新的值。属性的值必须是对象，如果是简单数据类型，则必须进行包装。
/**
* @param propertyName
* @param oldValue
* @param newValue
*/
public void firePropertyChange(String propertyName, Object oldValue, Object newValue) {
PropertyChangeSupport pcs;
synchronized (this) {
pcs = propertyChangeSupport;
}
if (pcs != null && (oldValue != null || newValue != null)) {
pcs.firePropertyChange(propertyName, oldValue, newValue);
}
}所有注册的监听器实现PropertyChangeListener接口，该接口中有一个方法。
public class RuntimeCfg implements PropertyChangeListener {
//部分代码省略
/**
* Handles changes to the Configuration this RuntimeCfg backs
* @param evt the PropertyChangeEvent
*/
public void propertyChange(final PropertyChangeEvent evt) {
try {
DynamicProperty.valueOf(evt.getPropertyName()).applyChange(evt, this);
} catch (IllegalArgumentException e) {
throw new IllegalStateException(evt.getPropertyName() + " can't be changed dynamically");
}
}
｝再来看看DynamicProperty做了什么。
/**
* Enum of all properties that can change once the Configuration is being used by a CacheManager
*/
private static enum DynamicProperty {
cacheManagerName {
@Override
void applyChange(final PropertyChangeEvent evt, final RuntimeCfg config) {
config.cacheManagerName = (String) evt.getNewValue();
}
},
defaultCacheConfiguration {
@Override
void applyChange(final PropertyChangeEvent evt, final RuntimeCfg config) {
LOG.debug("Default Cache Configuration has changed, previously created caches remain untouched");
}
},
maxBytesLocalHeap {
@Override
void applyChange(final PropertyChangeEvent evt, final RuntimeCfg config) {
ArrayList<ConfigError> errors = new ArrayList<ConfigError>();
Long newValue = (Long)evt.getNewValue();
if ((Long) evt.getOldValue() > (Long) evt.getNewValue()) {
// Double check for over-allocation again
for (Cache cache : getAllActiveCaches(config.cacheManager)) {
CacheConfiguration cacheConfiguration = cache.getCacheConfiguration();
errors.addAll(cacheConfiguration.validateCachePools(config.getConfiguration()));
errors.addAll(cacheConfiguration.verifyPoolAllocationsBeforeAddingTo(config.cacheManager,
newValue, config.getConfiguration().getMaxBytesLocalOffHeap(), config.getConfiguration().getMaxBytesLocalDisk(), null));
}
}
if (!errors.isEmpty()) {
throw new InvalidConfigurationException("Can't reduce CacheManager byte tuning by so much", errors);
}
// Recalculate % based caches
long cacheAllocated = 0;
for (Cache cache : getAllActiveCaches(config.cacheManager)) {
cache.getCacheConfiguration().configCachePools(config.getConfiguration());
long bytesLocalHeap = cache.getCacheConfiguration().getMaxBytesLocalHeap();
cacheAllocated += bytesLocalHeap;
}
config.cacheManager.getOnHeapPool().setMaxSize(newValue - cacheAllocated);
}
},
maxBytesLocalDisk {
@Override
void applyChange(final PropertyChangeEvent evt, final RuntimeCfg config) {
if ((Long)evt.getOldValue() > (Long)evt.getNewValue()) {
// Double check for over-allocation again
for (CacheConfiguration cacheConfiguration : config.getConfiguration().getCacheConfigurations().values()) {
cacheConfiguration.isMaxBytesLocalDiskPercentageSet();
}
}
config.cacheManager.getOnDiskPool().setMaxSize((Long) evt.getNewValue());
// Recalculate % based caches ?
}
};
abstract void applyChange(PropertyChangeEvent evt, RuntimeCfg config);
}使用这个类管理监听器的好处是，它是线程安全的。如果使用一个循环体来set Bean的属性，则这个类可以保证所有监听器执行触发事件的有序。 还有一个好处是，这个类支持 fire 带索引的属性改变事件（详见 java.bean.IndexedPropertyChangeEvent ）。此时向注册的监听器发送一个 PropertyChangeEvent 的方法为：
void fireIndexedPropertyChange(String PropertyName,int index,Object oldValue,Object newValue);来源：oschina
链接：https://my.oschina.net/u/1050156/blog/185683