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.
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 sDownloadingSet; //软引用内存缓存 private static Map > 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 (); sImageCache = new HashMap >(); 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 > 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 > 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)); 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 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)); } 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 } } }); } }