三级缓存图片类

package com.azy.xiaolong.news.util;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;


import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Build;
import android.support.v4.util.LruCache;

public class BitmapLoad {

    private static LruCache<String, Bitmap> cache;
    private static File cachePath;
    private BitmapCallback callback;
    public BitmapLoad(Context context) {
        int size=(int) (Runtime.getRuntime().maxMemory()/8);
        if(cache==null){
            cache=new LruCache<String, Bitmap>(size){
                @Override
                protected int sizeOf(String key, Bitmap value) {
                    return value.getRowBytes()*value.getHeight();
                }
            };
        }

        if(cachePath==null){
            cachePath=context.getExternalCacheDir();
            if(!cachePath.exists()){
                cachePath.mkdirs();
            }
        }
    }

    //加载图片
    @SuppressWarnings("unused")
    public Bitmap LoadBitmap(String url, BitmapCallback callback) {
        this.callback = callback;
        // 从缓存中取图片
        Bitmap bitmap = null;
        bitmap = getBitmapToCache(url);
        if (bitmap != null) {
            return bitmap;
        }
        // 从SD卡内存中取图片
        bitmap = getBitmapToSdcard(url);
        if (bitmap != null) {
            return bitmap;
        }

        // 从网络下载
        getBitmapNet(url, callback);
        return null;
    }

    // 从缓存中取图片
    private Bitmap getBitmapToCache(String url) {
        return cache.get(url);
    }

    // 从缓存中存图片
    private void putBitmapToCache(String url, Bitmap bitmap) {
        cache.put(url, bitmap);
    }

    // 从SD卡内存中取图片
    private Bitmap getBitmapToSdcard(String url) {
        String fileName = url.substring(url.lastIndexOf('/') + 1, url.length());
        File file = new File(cachePath, fileName);
        if (file.exists()) {
            Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
            putBitmapToCache(url, bitmap);
            return bitmap;
        }
        return null;

    }

    // 从SD卡内存中存图片
    private void putBitmapToSdcard(String url, Bitmap bitmap) {
        String fileName = url.substring(url.lastIndexOf('/') + 1, url.length());
        File file = new File(cachePath, fileName);
        OutputStream os;
        try {
            os = new FileOutputStream(file);
            bitmap.compress(CompressFormat.JPEG, 100, os);
            os.flush();
            os.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 下载完成后回调的接口
    public interface BitmapCallback {
        public void BitmapOk(String str, Bitmap bitmap);

        public void BitmapError(String url);
    }

    // 从网络下载
    @SuppressLint("NewApi")
    private void getBitmapNet(String url, BitmapCallback callback) {
        BitmapAsyn2 asyn = new BitmapAsyn2();
        if (Build.VERSION.SDK_INT >= 11) {
            asyn.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);
        } else {
            asyn.execute(url);
        }

    }

    // 异步任务类
    class BitmapAsyn2 extends AsyncTask<String, Void, Bitmap> {
        String url;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            this.url = params[0];
            InputStream is = HttpClientUtil
                    .httpGet2InputStream(params[0], null);
            if (is != null) {
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                if (bitmap != null) {
                    putBitmapToCache(url, bitmap);
                    putBitmapToSdcard(url, bitmap);
                    try {
                        is.close();
                        return bitmap;
                    } catch (IOException e) {
                    }
                }
            }
            return null;
        }

        @Override
        protected void onPostExecute(Bitmap result) {
            super.onPostExecute(result);
            if (result != null) {
                callback.BitmapOk(url, result);
            } else {
                callback.BitmapError(url);
            }
        }

    }

}