public abstract class AsyncTask<Params, Progress, Result> { private static final String LOG_TAG = "AsyncTask"; private static final int CORE_POOL_SIZE = 5; private static final int MAXIMUM_POOL_SIZE = 128; private static final int KEEP_ALIVE = 1; private static final ThreadFactory sThreadFactory = new ThreadFactory() {  private final AtomicInteger mCount = new AtomicInteger(1);  public Thread newThread(Runnable r) {   return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());  } };

 private static final InternalHandler sHandler = new InternalHandler(); mFuture = new FutureTask<Result>(mWorker) {   @Override   protected void More ...done() {    Message message;    Result result = null;    try {     result = get();    } catch (InterruptedException e) {     android.util.Log.w(LOG_TAG, e);    } catch (ExecutionException e) {     throw new RuntimeException("An error occured while executing doInBackground()",       e.getCause());    } catch (CancellationException e) {     message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,       new AsyncTaskResult<Result>(AsyncTask.this, (Result[]) null));     message.sendToTarget();     return;    } catch (Throwable t) {     throw new RuntimeException("An error occured while executing "       + "doInBackground()", t);    }    message = sHandler.obtainMessage(MESSAGE_POST_RESULT,      new AsyncTaskResult<Result>(AsyncTask.this, result));    message.sendToTarget();   }  }; private static class InternalHandler extends Handler {  @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})  @Override  public void More ...handleMessage(Message msg) {   AsyncTaskResult result = (AsyncTaskResult) msg.obj;   switch (msg.what) {    case MESSAGE_POST_RESULT:     // There is only one result     result.mTask.finish(result.mData[0]);     break;    case MESSAGE_POST_PROGRESS:     result.mTask.onProgressUpdate(result.mData);     break;    case MESSAGE_POST_CANCEL:     result.mTask.onCancelled();     break;   }  } }

import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URL;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.widget.ImageView;/** * 網絡緩存 *  * @author Ace * @date 2016-02-18 */public class NetCacheUtils { private LocalCacheUtils mLocalUtils; private MemoryCacheUtils mMemoryUtils; public NetCacheUtils(LocalCacheUtils localUtils,   MemoryCacheUtils memoryUtils) {  mLocalUtils = localUtils;  mMemoryUtils = memoryUtils; } public void getBitmapFromNet(ImageView imageView, String url) {  BitmapTask task = new BitmapTask();  task.execute(imageView, url); } /**  * AsyncTask是線程池+handler的封裝 第一個泛型: 傳參的參數類型類型(和doInBackground一致) 第二個泛型:  * 更新進度的參數類型(和onProgressUpdate一致) 第三個泛型: 返回結果的參數類型(和onPostExecute一致,  * 和doInBackground返回類型一致)  */ class BitmapTask extends AsyncTask<Object, Integer, Bitmap> {  private ImageView mImageView;  private String url;  // 主線程運行, 預加載  @Override  protected void onPreExecute() {   super.onPreExecute();  }  // 子線程運行, 異步加載邏輯在此方法中處理  @Override  protected Bitmap doInBackground(Object... params) {   mImageView = (ImageView) params[0];   url = (String) params[1];   mImageView.setTag(url);// 將imageView和url綁定在一起   // publishProgress(values)//通知進度   // 下載圖片   return download(url);  }  // 主線程運行, 更新進度  @Override  protected void onProgressUpdate(Integer... values) {   super.onProgressUpdate(values);  }  // 主線程運行, 更新主界面  @Override  protected void onPostExecute(Bitmap result) {   if (result != null) {    // 判斷當前圖片是否就是imageView要的圖片, 防止listview重用導致的圖片錯亂的情況出現    String bindUrl = (String) mImageView.getTag();    if (bindUrl.equals(url)) {     // 給imageView設置圖片     mImageView.setImageBitmap(result); // 將圖片保存在本地     mLocalUtils.setBitmapToLocal(result, url);     // 將圖片保存在內存     mMemoryUtils.setBitmapToMemory(url, result);    }   }  } } /**  * 下載圖片  *   * @param url  */ public Bitmap download(String url) {  HttpURLConnection conn = null;  try {   conn = (HttpURLConnection) (new URL(url).openConnection());   conn.setConnectTimeout(5000);   conn.setReadTimeout(5000);   conn.setRequestMethod("GET");   conn.connect();   int responseCode = conn.getResponseCode();   if (responseCode == 200) {    InputStream in = conn.getInputStream();    // 將流轉化為bitmap對象    Bitmap bitmap = BitmapFactory.decodeStream(in);    return bitmap;   }  } catch (Exception e) {   e.printStackTrace();  } finally {   if (conn != null) {    conn.disconnect();   }  }  return null; }}

* A cache that holds strong references to a limited number of values. Each time * a value is accessed, it is moved to the head of a queue. When a value is * added to a full cache, the value at the end of that queue is evicted and may * become eligible for garbage collection. * Cache保存一個強引用來限制內容數量，每當Item被訪問的時候，此Item就會移動到隊列的頭部。* 當cache已滿的時候加入新的item時，在隊列尾部的item會被回收。* <p>If your cached values hold resources that need to be explicitly released, * override {@link #entryRemoved}. * 如果你cache的某個值需要明確釋放，重寫entryRemoved() * <p>By default, the cache size is measured in the number of entries. Override * {@link #sizeOf} to size the cache in different units. For example, this cache * is limited to 4MiB of bitmaps: 默認cache大小是測量的item的數量，重寫sizeof計算不同item的* 大小。 {@code  * int cacheSize = 4 * 1024 * 1024; // 4MiB  * LruCache<String, Bitmap> bitmapCache = new LruCache<String, Bitmap>(cacheSize) {  *  protected int sizeOf(String key, Bitmap value) {  *   return value.getByteCount();  *  }  * }} -------------------------------------------------------------------<p>This class is thread-safe. Perform multiple cache operations atomically by * synchronizing on the cache: <pre> {@code * synchronized (cache) { * if (cache.get(key) == null) { * cache.put(key, value); * } * }}</pre> * 他是線程安全的,自動地執行多個緩存操作并且加鎖 -------------------------<p>This class does not allow null to be used as a key or value. A return * value of null from {@link #get}, {@link #put} or {@link #remove} is * unambiguous: the key was not in the cache.* 不允許key或者value為null* 當get（），put（），remove（）返回值為null時，key相應的項不在cache中

import android.graphics.Bitmap;import android.support.v4.util.LruCache;/** * 內存緩存工具類 *  * @author Ace * @date 2016-02-19 */public class MemoryCacheUtils { // Android 2.3 (API Level // 9)開始，垃圾回收器會更傾向于回收持有軟引用或弱引用的對象，這讓軟引用和弱引用變得不再可靠,建議用LruCache,它是強引用 private LruCache<String, Bitmap> mCache; public MemoryCacheUtils() {  int maxMemory = (int) Runtime.getRuntime().maxMemory();// 獲取虛擬機分配的最大內存                // 16M  // LRU 最近最少使用, 通過控制內存不要超過最大值(由開發者指定), 來解決內存溢出,就像上面翻譯的所說 如果cache滿了會清理最近最少使用的緩存對象  mCache = new LruCache<String, Bitmap>(maxMemory / 8) {   @Override   protected int sizeOf(String key, Bitmap value) {    // 計算一個bitmap的大小    int size = value.getRowBytes() * value.getHeight();// 每一行的字節數乘以高度    return size;   }  }; } public Bitmap getBitmapFromMemory(String url) {  return mCache.get(url); } public void setBitmapToMemory(String url, Bitmap bitmap) {  mCache.put(url, bitmap); }}

/** * 本地緩存工具類 *  * @author Ace * @date 2016-02-19 */public class LocalCacheUtils { // 圖片緩存的文件夾 public static final String DIR_PATH = Environment   .getExternalStorageDirectory().getAbsolutePath()   + "/ace_bitmap_cache"; public Bitmap getBitmapFromLocal(String url) {  try {   File file = new File(DIR_PATH, MD5Encoder.encode(url));   if (file.exists()) {    Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(      file));    return bitmap;   }  } catch (Exception e) {   e.printStackTrace();  }  return null; } public void setBitmapToLocal(Bitmap bitmap, String url) {  File dirFile = new File(DIR_PATH);  // 創建文件夾 文件夾不存在或者它不是文件夾 則創建一個文件夾.mkdirs,mkdir的區別在于假如文件夾有好幾層路徑的話,前者會創建缺失的父目錄 后者不會創建這些父目錄  if (!dirFile.exists() || !dirFile.isDirectory()) {   dirFile.mkdirs();  }  try {   File file = new File(DIR_PATH, MD5Encoder.encode(url));   // 將圖片壓縮保存在本地,參1:壓縮格式;參2:壓縮質量(0-100);參3:輸出流   bitmap.compress(CompressFormat.JPEG, 100,     new FileOutputStream(file));  } catch (Exception e) {   e.printStackTrace();  } }}

import java.security.MessageDigest;public class MD5Encoder {  public static String encode(String string) throws Exception {  byte[] hash = MessageDigest.getInstance("MD5").digest(string.getBytes("UTF-8"));  StringBuilder hex = new StringBuilder(hash.length * 2);  for (byte b : hash) {   if ((b & 0xFF) < 0x10) {    hex.append("0");   }   hex.append(Integer.toHexString(b & 0xFF));  }  return hex.toString(); }}

/** * 三級緩存工具類 *  * @author Ace * @date 2016-02-19 */public class MyBitmapUtils { // 網絡緩存工具類 private NetCacheUtils mNetUtils; // 本地緩存工具類 private LocalCacheUtils mLocalUtils; // 內存緩存工具類 private MemoryCacheUtils mMemoryUtils; public MyBitmapUtils() {  mMemoryUtils = new MemoryCacheUtils();  mLocalUtils = new LocalCacheUtils();  mNetUtils = new NetCacheUtils(mLocalUtils, mMemoryUtils); } public void display(ImageView imageView, String url) {  // 設置默認加載圖片  imageView.setImageResource(R.drawable.news_pic_default);  // 先從內存緩存加載  Bitmap bitmap = mMemoryUtils.getBitmapFromMemory(url);  if (bitmap != null) {   imageView.setImageBitmap(bitmap);   System.out.println("從內存讀取圖片啦...");   return;  }  // 再從本地緩存加載  bitmap = mLocalUtils.getBitmapFromLocal(url);  if (bitmap != null) {   imageView.setImageBitmap(bitmap);   System.out.println("從本地讀取圖片啦...");   // 給內存設置圖片   mMemoryUtils.setBitmapToMemory(url, bitmap);   return;  }  // 從網絡緩存加載  mNetUtils.getBitmapFromNet(imageView, url); }}