ehcache是一个分布式缓存框架
分布缓存
我们系统为了提高系统并发，性能、一般对系统进行分布式部署（集群部署方式）
不使用分布缓存，缓存的数据在各各服务单独存储，不方便系统开发。所以要使用分布式缓存对缓存数据进行集中管理。
mybatis无法实现分布式缓存，需要和其它分布式缓存框架进行整合。
整合方法(掌握)
mybatis提供了一个cache接口，如果要实现自己的缓存逻辑，实现cache接口开发即可。
mybatis和ehcache整合，mybatis和ehcache整合包中提供了一个cache接口的实现类。
package org.apache.ibatis.cache;
import java.util.concurrent.locks.ReadWriteLock;
/**
* SPI for cache providers.
*
* One instance of cache will be created for each namespace.
*
* The cache implementation must have a constructor that receives the cache id as an String parameter.
*
* MyBatis will pass the namespace as id to the constructor.
*
* <pre>
* public MyCache(final String id) {
* if (id == null) {
* throw new IllegalArgumentException("Cache instances require an ID");
* }
* this.id = id;
* initialize();
* }
* </pre>
*
* @author Clinton Begin
*/
public interface Cache {
/**
* @return The identifier of this cache
*/
String getId();
/**
* @param key Can be any object but usually it is a {@link CacheKey}
* @param value The result of a select.
*/
void putObject(Object key, Object value);
/**
* @param key The key
* @return The object stored in the cache.
*/
Object getObject(Object key);
/**
* Optional. It is not called by the core.
*
* @param key The key
* @return The object that was removed
*/
Object removeObject(Object key);
/**
* Clears this cache instance
*/
void clear();
/**
* Optional. This method is not called by the core.
*
* @return The number of elements stored in the cache (not its capacity).
*/
int getSize();
/**
* Optional. As of 3.2.6 this method is no longer called by the core.
*
* Any locking needed by the cache must be provided internally by the cache provider.
*
* @return A ReadWriteLock
*/
ReadWriteLock getReadWriteLock();
}
mybatis默认实现cache类是：
package org.apache.ibatis.cache.impl;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.cache.CacheException;
/**
* @author Clinton Begin
*/
public class PerpetualCache implements Cache {
private String id;
private Map<Object, Object> cache = new HashMap<Object, Object>();
public PerpetualCache(String id) {
this.id = id;
}
public String getId() {
return id;
}
public int getSize() {
return cache.size();
}
public void putObject(Object key, Object value) {
cache.put(key, value);
}
public Object getObject(Object key) {
return cache.get(key);
}
public Object removeObject(Object key) {
return cache.remove(key);
}
public void clear() {
cache.clear();
}
public ReadWriteLock getReadWriteLock() {
return null;
}
public boolean equals(Object o) {
if (getId() == null) throw new CacheException("Cache instances require an ID.");
if (this == o) return true;
if (!(o instanceof Cache)) return false;
Cache otherCache = (Cache) o;
return getId().equals(otherCache.getId());
}
public int hashCode() {
if (getId() == null) throw new CacheException("Cache instances require an ID.");
return getId().hashCode();
}
}
整合ehcache
- 加入ehcache包
- ehcache-core-2.6.5.jar
- mybatis-ehcache-1.0.2.jar
配置mapper中cache中的type为ehcache对cache接口的实现类型
<!-- 开启本mapper的namespace下的二级缓存
type：指定cache接口的实现类的类型，mybatis默认使用PerpetualCache
要和ehcache整合，需要配置type为ehcache实现cache接口的类型
<cache />
-->
<cache type="org.mybatis.caches.ehcache.EhcacheCache"/>
加入ehcache的配置文件
在classpath下配置ehcache.xml
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
<diskStore path="F:\develop\ehcache" />
<defaultCache
maxElementsInMemory="1000"
maxElementsOnDisk="10000000"
eternal="false"
overflowToDisk="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
diskExpiryThreadIntervalSeconds="120"
memoryStoreEvictionPolicy="LRU">
</defaultCache>
</ehcache>
