【Mybatis】LRU缓冲实现
LRU (least recently used) 即“最近最少使用”缓冲淘汰算法。
Mybatis 的 LRUCache 是利用 java 的基础工具包LinkedHashMap
特性二次开发完成。
Cache 接口定义
public interface Cache {
/**
* 缓冲 ID
*/
String getId();
/**
* 存储数据
*/
void putObject(Object key, Object value);
/**
* 获取数据
*/
Object getObject(Object key);
/**
* 删除数据
*/
Object removeObject(Object key);
/**
* 清空缓冲
*/
void clear();
/**
* 获取缓冲大小
*/
int getSize();
ReadWriteLock getReadWriteLock();
}
LRUCache 实现类
LRUCache 实现 Cache 接口
package org.apache.ibatis.cache.decorators;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import org.apache.ibatis.cache.Cache;
/**
* Lru (least recently used) cache decorator
*/
public class LruCache implements Cache {
private final Cache delegate;
private Map<Object, Object> keyMap;
private Object eldestKey;
public LruCache(Cache delegate) {
this.delegate = delegate;
setSize(1024);
}
@Override
public String getId() {
return delegate.getId();
}
@Override
public int getSize() {
return delegate.getSize();
}
public void setSize(final int size) {
keyMap = new LinkedHashMap<Object, Object>(size, .75F, true) {
private static final long serialVersionUID = 4267176411845948333L;
@Override
protected boolean removeEldestEntry(Map.Entry<Object, Object> eldest) {
boolean tooBig = size() > size;
if (tooBig) {
eldestKey = eldest.getKey();
}
return tooBig;
}
};
}
@Override
public void putObject(Object key, Object value) {
delegate.putObject(key, value);
cycleKeyList(key);
}
@Override
public Object getObject(Object key) {
keyMap.get(key); //touch
return delegate.getObject(key);
}
@Override
public Object removeObject(Object key) {
return delegate.removeObject(key);
}
@Override
public void clear() {
delegate.clear();
keyMap.clear();
}
@Override
public ReadWriteLock getReadWriteLock() {
return null;
}
private void cycleKeyList(Object key) {
keyMap.put(key, key);
if (eldestKey != null) {
delegate.removeObject(eldestKey);
eldestKey = null;
}
}
}