~~~ /** * Copyright 2009-2019 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.ibatis.cache.decorators; import java.util.LinkedHashMap; import java.util.Map; import org.apache.ibatis.cache.Cache; /** * Lru (least recently used) cache decorator. * * @author Clinton Begin */ 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(); } private void cycleKeyList(Object key) { keyMap.put(key, key); //也实现了长度溢出删除 if (eldestKey != null) { delegate.removeObject(eldestKey); eldestKey = null; } } } ~~~