装饰器模式很有意思，有点想代理一样，每一层代理加点东西，搞个新包装。但是实际上里面的产品还是厂家生产的。
/**
* 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 org.apache.ibatis.cache.Cache;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
/**
* @author Clinton Begin
*/
public class LoggingCache implements Cache {
private final Log log;
private final Cache delegate;
protected int requests = 0;
protected int hits = 0;
public LoggingCache(Cache delegate) {
this.delegate = delegate;
this.log = LogFactory.getLog(getId());
}
@Override
public String getId() {
return delegate.getId();
}
@Override
public int getSize() {
return delegate.getSize();
}
@Override
public void putObject(Object key, Object object) {
delegate.putObject(key, object);
}
@Override
public Object getObject(Object key) {
requests++;
final Object value = delegate.getObject(key);
if (value != null) {
hits++;
}
if (log.isDebugEnabled()) {
log.debug("Cache Hit Ratio [" + getId() + "]: " + getHitRatio());
}
return value;
}
@Override
public Object removeObject(Object key) {
return delegate.removeObject(key);
}
@Override
public void clear() {
delegate.clear();
}
@Override
public int hashCode() {
return delegate.hashCode();
}
@Override
public boolean equals(Object obj) {
return delegate.equals(obj);
}
private double getHitRatio() {
return (double) hits / (double) requests;
}
}
这是一个最简单明了的装饰器应用，纯粹就是加一个日志打印。
if (log.isDebugEnabled()) {
log.debug("Cache Hit Ratio [" + getId() + "]: " + getHitRatio());
}
使用
@Test
void shouldDemonstrateHowAllObjectsAreFlushedAfterBasedOnTime() throws Exception {
Cache cache = new PerpetualCache("DefaultCache");
cache = new ScheduledCache(cache);
((ScheduledCache) cache).setClearInterval(2500);
cache = new LoggingCache(cache);
for (int i = 0; i < 100; i++) {
cache.putObject(i, i);
assertEquals(i, cache.getObject(i));
}
Thread.sleep(5000);
assertEquals(0, cache.getSize());
}
Mybatis3源码深度解析
可以看出来厂家就是PerpetualCache
/**
* 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.impl;
import java.util.HashMap;
import java.util.Map;
import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.cache.CacheException;
/**
* @author Clinton Begin
*/
public class PerpetualCache implements Cache {
private final String id;
private final Map<Object, Object> cache = new HashMap<>();
public PerpetualCache(String id) {
this.id = id;
}
@Override
public String getId() {
return id;
}
@Override
public int getSize() {
return cache.size();
}
@Override
public void putObject(Object key, Object value) {
cache.put(key, value);
}
@Override
public Object getObject(Object key) {
return cache.get(key);
}
@Override
public Object removeObject(Object key) {
return cache.remove(key);
}
@Override
public void clear() {
cache.clear();
}
@Override
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());
}
@Override
public int hashCode() {
if (getId() == null) {
throw new CacheException("Cache instances require an ID.");
}
return getId().hashCode();
}
}
当然底层逻辑其实很简单，就是一个HashMap.
让我迷惑的就是下面这个装饰器
/**
* 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.Deque;
import java.util.LinkedList;
import org.apache.ibatis.cache.Cache;
/**
* FIFO (first in, first out) cache decorator.
*
* @author Clinton Begin
*/
public class FifoCache implements Cache {
private final Cache delegate;
private final Deque<Object> keyList;
private int size;
public FifoCache(Cache delegate) {
this.delegate = delegate;
this.keyList = new LinkedList<>();
this.size = 1024;
}
@Override
public String getId() {
return delegate.getId();
}
@Override
public int getSize() {
return delegate.getSize();
}
public void setSize(int size) {
this.size = size;
}
@Override
public void putObject(Object key, Object value) {
cycleKeyList(key);
delegate.putObject(key, value);
}
@Override
public Object getObject(Object key) {
return delegate.getObject(key);
}
@Override
public Object removeObject(Object key) {
return delegate.removeObject(key);
}
@Override
public void clear() {
delegate.clear();
keyList.clear();
}
private void cycleKeyList(Object key) {
keyList.addLast(key);
if (keyList.size() > size) {
Object oldestKey = keyList.removeFirst();
delegate.removeObject(oldestKey);
}
}
}
下面这个队列的实际作用是啥，只有put的时候有操作，但是get的时候完全没有看出来啥作用。
private final Deque<Object> keyList;
