Android Open Source - Alfred4Android Soft Cache

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License

The source code is released under:
Apache License
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Java Source Code

package com.toraleap.collimator.util;
/*ww w.  java  2 s.c om*/
import java.lang.ref.SoftReference;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingQueue;

import android.os.Handler;
import android.os.Message;
import android.util.Log;

/**
 * ????????????????????????????? request ????????????????????
 * @author    uestc.Mobius <mobius@toraleap.com>
 * @version  2010.1104
 *
 * @param <K>  ??????????
 * @param <V>  ?????????
 */
public abstract class SoftCache<K, V> {

  private static final int MESSAGE_FIRST = 200;
  public static final int MESSAGE_CACHE_GOT = MESSAGE_FIRST + 1;
  public static final int MESSAGE_QUEUE_FINISHED = MESSAGE_FIRST + 2;
  
    private final ConcurrentHashMap<K, SoftReference<V>> cache = new ConcurrentHashMap<K, SoftReference<V>>();
    private final LinkedBlockingQueue<K> queue = new LinkedBlockingQueue<K>();
    private final SoftReference<V> loadingHolder = new SoftReference<V>(null);
    private final Handler callback;
    private final Thread thread = new Thread() {
    public void run() {
      K key;
      while (true) {
        try {
          key = queue.take();
            requestAndCache(key);
            if (!isInterrupted()) {
              sendHandlerMessage(MESSAGE_CACHE_GOT, 0, 0, key);
              if (queue.size() == 0) sendHandlerMessage(MESSAGE_QUEUE_FINISHED, 0, 0, null);
            } else {
              clearQueue();
            }
        } catch (InterruptedException e) {
          e.printStackTrace();
          clearQueue();
        }
      }
    }
  };

  /**
   * ?????????????????????
   * @param callback  ???????????? Handler
   */
    public SoftCache(Handler callback) {
      this.callback = callback;
      thread.setDaemon(true);
      thread.start();
    }
    
    /**
     * ????????????????????????????????????????????????? ???? ?????????????????????????????????????????????????????????????? Handler ???? MESSAGE_CACHE_GOT ??????????????????????????? Handler ???? MESSAGE_QUEUE_FINISHED ?????????????????????? getDefault ???????
     * @param key  ?????????
     * @return ?????????????????
     */
    public V get(K key) {
      SoftReference<V> ref = cache.get(key);
      // ?????????????????????
      if (ref == null) {
        offerRequest(key);
        return getDefault();
      }
      // ????????????
      if (ref == loadingHolder) {
        return getDefault();
      }
      V value = ref.get();
      // ?????????????????????
      if (value == null) {
        offerRequest(key);
        return getDefault();
      }
      // ?????????????
      return value;
    }
    
    /**
     * ???????????????????????????????????????? Handler ???? MESSAGE_CACHE_GOT ??????????????? MESSAGE_QUEUE_FINISHED ?????
     */
    public void interrupt() {
      thread.interrupt();
    }
    
    /**
     * ????????????????????????????????????????????????????????? null????????????????????
     * @param key  ??????????
     * @return  ??????????????? null
     */
    V getCache(K key) {
      SoftReference<V> ref = cache.get(key);
      if (ref == null) return null;
      return ref.get();
    }

    /**
     * ???????????????????????????????????????
     * @param key  ?????
     * @param value    ???????????
     * @return ???????????
     */
    V putCache(K key, V value) {
      if (value == null) return null;
      cache.put(key, new SoftReference<V>(value));
      return value;
    }
    
    /**
     * ????????????????????????????????????????????????????????????????????????????
     * @param key  ??????????
     * @return ??????
     */
    V requestAndCache(K key) {
      V value = getCache(key);
      // ???????????????????
      if (value == null) {
          return putCache(key, request(key));
      }
      // ?????????????
      return value;      
    }
    
    /**
     * ??????????????????????
     * @param key  ??????????
     */
    private void offerRequest(K key) {
      cache.put(key, loadingHolder);
      queue.offer(key);
      if (getMaxQueueLength() > 0 && queue.size() > getMaxQueueLength()) {
        cache.remove(queue.remove());
      }
    }
    
    /**
     * ???????????????????????????????????
     */
    private void clearQueue() {
      while (true) {
        K key = queue.poll();
        if (key == null) break;
        cache.remove(key);
      }
    }
    
  /**
   * ???????????????????????
   * @param what  ???????
   * @param arg1  ???????1 (????????????)
   * @param arg2  ???????2 (????????????)
   * @param obj  ?????????? (????????????)
   */
  private void sendHandlerMessage(int what, int arg1, int arg2, Object obj) {
    if (null != callback) {
      Message msg = Message.obtain();
      msg.what = what;
      msg.arg1 = arg1;
      msg.arg2 = arg2;
      msg.obj = obj;
      callback.sendMessage(msg);
    }
  }
  
  /**
   * ??????????????????????????????????? null??
   * @return ??? null ??????
   */
  V getDefault() {
    return null;
  }
  
  /**
   * ????????????????????????????????????????????????????????????????????????????(-1)??
   * @return
   */
  int getMaxQueueLength() {
    return -1;
  }
    
    /**
     * ?????????????????????????????????????????????????
     * @param key  ?????????
     * @return ??????????
     */
    abstract V request(K key);
}
Java Source Code List
