android 下载网络图片并缓存

异步下载网络图片，并提供是否缓存至内存或外部文件的功能

异步加载类AsyncImageLoader

public void downloadImage(final String url, final ImageCallback callback);

public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback);

public void setCache2File(boolean flag);

public void setCachedDir(String dir);

图片下载和缓存实现类LoaderImpl

1.AsyncImageLoader.java

 package com.imagecache;

 import java.lang.ref.SoftReference;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;

 import android.content.Context;
 import android.graphics.Bitmap;
 import android.os.Handler;
 import android.util.Log;

 public class AsyncImageLoader {
     //保存正在下载的图片URL集合，避免重复下载用
     private static HashSet<String> sDownloadingSet;
     //软引用内存缓存
     private static Map<String,SoftReference<Bitmap>> sImageCache;
     //图片三种获取方式管理者，网络URL获取、内存缓存获取、外部文件缓存获取
     private static LoaderImpl impl;
     //线程池相关
     private static ExecutorService sExecutorService;

     //通知UI线程图片获取ok时使用
     private Handler handler; 

     /**
      * 异步加载图片完毕的回调接口
      */
     public interface ImageCallback{
         /**
          * 回调函数
          * @param bitmap: may be null!
          * @param imageUrl
          */
         public void onImageLoaded(Bitmap bitmap, String imageUrl);
     }

     static{
         sDownloadingSet = new HashSet<String>();
         sImageCache = new HashMap<String,SoftReference<Bitmap>>();
         impl = new LoaderImpl(sImageCache);
     }

     public AsyncImageLoader(Context context){
         handler = new Handler();
         startThreadPoolIfNecessary();

         String defaultDir = context.getCacheDir().getAbsolutePath();
         setCachedDir(defaultDir);
     }

     /**
      * 是否缓存图片至/data/data/package/cache/目录
      * 默认不缓存
      */
     public void setCache2File(boolean flag){
         impl.setCache2File(flag);
     }

     /**
      * 设置缓存路径，setCache2File(true)时有效
      */
     public void setCachedDir(String dir){
         impl.setCachedDir(dir);
     }

     /**开启线程池*/
     public static void startThreadPoolIfNecessary(){
         if(sExecutorService == null || sExecutorService.isShutdown() || sExecutorService.isTerminated()){
             sExecutorService = Executors.newFixedThreadPool(3);
             //sExecutorService = Executors.newSingleThreadExecutor();
         }
     }

     /**
      * 异步下载图片，并缓存到memory中
      * @param url
      * @param callback    see ImageCallback interface
      */
     public void downloadImage(final String url, final ImageCallback callback){
         downloadImage(url, true, callback);
     }

     /**
      *
      * @param url
      * @param cache2Memory 是否缓存至memory中
      * @param callback
      */
     public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback){
         if(sDownloadingSet.contains(url)){
             Log.i("AsyncImageLoader", "###该图片正在下载，不能重复下载！");
             return;
         }

         Bitmap bitmap = impl.getBitmapFromMemory(url);
         if(bitmap != null){
             if(callback != null){
                 callback.onImageLoaded(bitmap, url);
             }
         }else{
             //从网络端下载图片
             sDownloadingSet.add(url);
             sExecutorService.submit(new Runnable(){
                 @Override
                 public void run() {
                     final Bitmap bitmap = impl.getBitmapFromUrl(url, cache2Memory);
                     handler.post(new Runnable(){
                         @Override
                         public void run(){
                             if(callback != null)
                                 callback.onImageLoaded(bitmap, url);
                             sDownloadingSet.remove(url);
                         }
                     });
                 }
             });
         }
     }

     /**
      * 预加载下一张图片，缓存至memory中
      * @param url
      */
     public void preLoadNextImage(final String url){
         //将callback置为空，只将bitmap缓存到memory即可。
         downloadImage(url, null);
     }

 }

2.LoaderImpl.java

 package com.imagecache;

 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.UnsupportedEncodingException;
 import java.lang.ref.SoftReference;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.Map;

 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;

 /**
  *
  * @author Administrator
  * @desc 异步加载图片管理器
  *
  */
 public class LoaderImpl {
     //内存中的软应用缓存
     private Map<String, SoftReference<Bitmap>> imageCache;

     //是否缓存图片至本地文件
     private boolean cache2FileFlag = false;

     //缓存目录,默认是/data/data/package/cache/目录
     private String cachedDir;

     public LoaderImpl(Map<String, SoftReference<Bitmap>> imageCache){
         this.imageCache = imageCache;
     }

     /**
      * 是否缓存图片至外部文件
      * @param flag
      */
     public void setCache2File(boolean flag){
         cache2FileFlag = flag;
     }

     /**
      * 设置缓存图片到外部文件的路径
      * @param cacheDir
      */
     public void setCachedDir(String cacheDir){
         this.cachedDir = cacheDir;
     }

     /**
      * 从网络端下载图片
      * @param url 网络图片的URL地址
      * @param cache2Memory 是否缓存(缓存在内存中)
      * @return bitmap 图片bitmap结构
      *
      */
     public Bitmap getBitmapFromUrl(String url, boolean cache2Memory){
         Bitmap bitmap = null;
         try{
             URL u = new URL(url);
             HttpURLConnection conn = (HttpURLConnection)u.openConnection();
             InputStream is = conn.getInputStream();
             bitmap = BitmapFactory.decodeStream(is);

             if(cache2Memory){
                 //1.缓存bitmap至内存软引用中
                 imageCache.put(url, new SoftReference<Bitmap>(bitmap));
                 if(cache2FileFlag){
                     //2.缓存bitmap至/data/data/packageName/cache/文件夹中
                     String fileName = getMD5Str(url);
                     String filePath = this.cachedDir + "/" +fileName;
                     FileOutputStream fos = new FileOutputStream(filePath);
                     bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
                 }
             }

             is.close();
             conn.disconnect();
             return bitmap;
         }catch(IOException e){
             e.printStackTrace();
             return null;
         }
     }

     /**
      * 从内存缓存中获取bitmap
      * @param url
      * @return bitmap or null.
      */
     public Bitmap getBitmapFromMemory(String url){
         Bitmap bitmap = null;
         if(imageCache.containsKey(url)){
             synchronized(imageCache){
                 SoftReference<Bitmap> bitmapRef = imageCache.get(url);
                 if(bitmapRef != null){
                     bitmap = bitmapRef.get();
                     return bitmap;
                 }
             }
         }
         //从外部缓存文件读取
         if(cache2FileFlag){
             bitmap = getBitmapFromFile(url);
             if(bitmap != null)
                 imageCache.put(url, new SoftReference<Bitmap>(bitmap));
         }

         return bitmap;
     }

     /**
      * 从外部文件缓存中获取bitmap
      * @param url
      * @return
      */
     private Bitmap getBitmapFromFile(String url){
         Bitmap bitmap = null;
         String fileName = getMD5Str(url);
         if(fileName == null)
             return null;

         String filePath = cachedDir + "/" + fileName;

         try {
             FileInputStream fis = new FileInputStream(filePath);
             bitmap = BitmapFactory.decodeStream(fis);
         } catch (FileNotFoundException e) {
             e.printStackTrace();
             bitmap = null;
         }
         return bitmap;
     }

     /**
      * MD5 加密
      */
     private static String getMD5Str(String str) {
         MessageDigest messageDigest = null;
         try {
             messageDigest = MessageDigest.getInstance("MD5");
             messageDigest.reset();
             messageDigest.update(str.getBytes("UTF-8"));
         } catch (NoSuchAlgorithmException e) {
             System.out.println("NoSuchAlgorithmException caught!");
             return null;
         } catch (UnsupportedEncodingException e) {
             e.printStackTrace();
             return null;
         }   

         byte[] byteArray = messageDigest.digest();
         StringBuffer md5StrBuff = new StringBuffer();
         for (int i = 0; i < byteArray.length; i++) {
             if (Integer.toHexString(0xFF & byteArray[i]).length() == 1)
                 md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));
             else
                 md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));
         }   

         return md5StrBuff.toString();
     }  

     /**
      * MD5 加密
     private static String getMD5Str(Object...objects){
         StringBuilder stringBuilder=new StringBuilder();
         for (Object object : objects) {
             stringBuilder.append(object.toString());
         }
         return getMD5Str(stringBuilder.toString());
     }*/
 }

3.测试Activity

 package com.imagecache;

 import android.app.Activity;
 import android.graphics.Bitmap;
 import android.os.Bundle;
 import android.widget.ImageView;

 public class MainActivity extends Activity {
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);

         final ImageView iv = (ImageView)findViewById(R.id.iv);
         //网络图片地址
         String imgUrl = "http://...";

         //for test
         AsyncImageLoader loader = new AsyncImageLoader(getApplicationContext());

         //将图片缓存至外部文件中
         loader.setCache2File(true);    //false
         //设置外部缓存文件夹
         loader.setCachedDir(this.getCacheDir().getAbsolutePath());

         //下载图片，第二个参数是否缓存至内存中
         loader.downloadImage(imgUrl, true/*false*/, new AsyncImageLoader.ImageCallback() {
             @Override
             public void onImageLoaded(Bitmap bitmap, String imageUrl) {
                 if(bitmap != null){
                     iv.setImageBitmap(bitmap);
                 }else{
                     //下载失败，设置默认图片
                 }
             }
         });
     }

 }