/*
* Copyright (C) 2010-2101 Alibaba Group Holding Limited.
*
* 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 com.alibaba.otter.shared.common.utils.cache;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;
import com.google.common.collect.MapMaker;
/**
* 简单内存镜像实现
*
* <pre>
* 1. 使用hashMap做为存储
* 2. 支持时间戳作为版本号
* 3. 支持ComputeFunction，在get结果为null允许进行回调处理
* </pre>
*/
public class ExtensionMemoryMirror<KEY, VALUE> {
private final Map<KEY, VALUE> store;
private final ComputeFunction<KEY, VALUE> function;
public ExtensionMemoryMirror(ComputeFunction<KEY, VALUE> function){
this.function = function;
store = new MapMaker().makeMap();
}
public synchronized VALUE get(KEY key) {
if (store.containsKey(key)) {
KEY oldKey = null;
for (KEY k : store.keySet()) {
if (k.equals(key)) {
oldKey = k;
break;
}
}
if (((Comparable) key).compareTo(oldKey) > 0) {
VALUE result = function.apply(key);
// 一定要先删除key，否则put时key不会被更新，对应的时间戳一直为老对象
remove(key);
put(key, result);
return result;
} else {
return store.get(key);
}
} else {
VALUE result = function.apply(key);
remove(key);
put(key, result);
return result;
}
}
public synchronized void put(KEY key, VALUE value) {
store.put(getKey(key), value);
}
public synchronized void remove(Object key) {
store.remove(getKey(key));
}
public synchronized void clear() {
store.clear();
}
public Iterator getKeys() {
return store.keySet().iterator();
}
public Set<Entry<KEY, VALUE>> entrySet() {
return store.entrySet();
}
public int size() {
return store.size();
}
private KEY getKey(Object key) {
if (key == null) {
throw new IllegalArgumentException("Cache key not be null");
}
return (KEY) key;
}
public static interface ComputeFunction<KEY, VALUE> {
VALUE apply(KEY key);
}
}