android下载网络图片并缓存

来源：互联网发布：软件使用说明编辑：程序博客网时间：2024/06/05 19:37

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

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

    /**              *               * @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

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              }          }      });  }  }

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