android中图片内存缓存的工具类的实现

package com.demo.loading;

import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.concurrent.ConcurrentHashMap;

import android.graphics.Bitmap;

/****
* 内存中的缓存
****/
public class ImageMemoryCache {
private static final int HARD_CACHE_CAPACITY = 30;

private HashMap<String, Bitmap> mHardBitmapCache;

private final static ConcurrentHashMap<String, SoftReference<Bitmap>> mSoftBitmapCache =

new ConcurrentHashMap<String, SoftReference<Bitmap>>(
HARD_CACHE_CAPACITY / 2);

public ImageMemoryCache() {
mHardBitmapCache = new LinkedHashMap<String, Bitmap>(
HARD_CACHE_CAPACITY / 2, 0.75f, true) {
private static final long serialVersionUID = 1L;

@Override
protected boolean removeEldestEntry(
LinkedHashMap.Entry<String, Bitmap> eldest) {
if (size() > HARD_CACHE_CAPACITY) {
// Entries push-out of hard reference cache are transferred
// to soft reference cache
mSoftBitmapCache.put(eldest.getKey(),
new SoftReference<Bitmap>(eldest.getValue()));
return true;
} else
return false;
}
};
}

/**
* 从缓存中获取图片
*/
public Bitmap getBitmapFromCache(String url) {
// 先从mHardBitmapCache缓存中获取
synchronized (mHardBitmapCache) {
final Bitmap bitmap = mHardBitmapCache.get(url);
if (bitmap != null) {
// 如果找到的话，把元素移到linkedhashmap的最前面，从而保证在LRU算法中是最后被删除
mHardBitmapCache.remove(url);
mHardBitmapCache.put(url, bitmap);
return bitmap;
}
}

// 如果mHardBitmapCache中找不到，到mSoftBitmapCache中找
SoftReference<Bitmap> bitmapReference = mSoftBitmapCache.get(url);
if (bitmapReference != null) {
final Bitmap bitmap = bitmapReference.get();
if (bitmap != null) {
// 将图片移回硬缓存
mHardBitmapCache.put(url, bitmap);
mSoftBitmapCache.remove(url);
return bitmap;
} else {
mSoftBitmapCache.remove(url);
}
}
return null;
}

/*** 添加图片到缓存 ***/
public void addBitmapToCache(String url, Bitmap bitmap) {
if (bitmap != null) {
synchronized (mHardBitmapCache) {
mHardBitmapCache.put(url, bitmap);
}
}
}
}