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 callbacksee 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(){@Overridepublic void run() {final Bitmap bitmap = impl.getBitmapFromUrl(url, cache2Memory);handler.post(new Runnable(){@Overridepublic 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() {@Overridepublic 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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