LoggingCache.java

/*
 *    Copyright 2009-2014 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.concurrent.locks.ReadWriteLock;

import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;

/**
 * @author Clinton Begin
 */
/**
 * 日志缓存
 * 添加功能：取缓存时打印命中率
 *
 */
public class LoggingCache implements Cache {

  //用的mybatis自己的抽象Log
  private Log log;  
  private 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);
  }

  //目的就是getObject时，打印命中率
  @Override
  public Object getObject(Object key) {
      //访问一次requests加一
    requests++;
    final Object value = delegate.getObject(key);
    //命中了则hits加一
    if (value != null) {
      hits++;
    }
    if (log.isDebugEnabled()) {
        //就是打印命中率 hits/requests
      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 ReadWriteLock getReadWriteLock() {
    return null;
  }

  @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;
  }

}