Java tutorial
/* * Copyright (C) 2010 The Android Open Source Project * Copyright (C) 2011 Peter Kuterna * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package net.peterkuterna.android.apps.devoxxfrsched.util; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.lang.ref.SoftReference; import java.lang.ref.WeakReference; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.concurrent.ConcurrentHashMap; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.HttpStatus; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.util.EntityUtils; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.Drawable; import android.os.AsyncTask; import android.os.Environment; import android.os.Handler; import android.util.Log; import android.widget.ImageView; /** * This helper class download images from the Internet and binds those with the * provided ImageView. * * <p> * It requires the INTERNET permission, which should be added to your * application's manifest file. * </p> * * A local cache of downloaded images is maintained internally to improve * performance. */ public class ImageDownloader { private static final String TAG = "ImageDownloader"; private Context mContext; private HttpClient mClient; public ImageDownloader(Context context) { this.mContext = context; this.mClient = HttpUtils.getHttpClient(context); } /** * Download the specified image from the Internet and binds it to the * provided ImageView. The binding is immediate if the image is found in the * cache and will be done asynchronously otherwise. A null bitmap will be * associated to the ImageView if an error occurs. * * @param url * The URL of the image to download. * @param imageView * The ImageView to bind the downloaded image to. * @param emptyResId * The resource id to use as empty view */ public void download(String url, ImageView imageView, int emptyResId) { resetPurgeTimer(); Bitmap bitmap = getBitmapFromCache(url); if (bitmap == null) { forceDownload(url, imageView, emptyResId); } else { cancelPotentialDownload(url, imageView); imageView.setImageBitmap(bitmap); } } /** * Same as download but the image is always downloaded and the cache is not * used. Kept private at the moment as its interest is not clear. */ private void forceDownload(String url, ImageView imageView, int emptyResId) { // State sanity: url is guaranteed to never be null in // DownloadedDrawable and cache keys. if (url == null) { imageView.setImageDrawable(null); return; } if (cancelPotentialDownload(url, imageView)) { BitmapDownloaderTask task = new BitmapDownloaderTask(imageView); DownloadedDrawable downloadedDrawable = new DownloadedDrawable(mContext, task, emptyResId); imageView.setImageDrawable(downloadedDrawable); imageView.setMinimumHeight(156); task.execute(url); } } /** * Returns true if the current download has been canceled or if there was no * download in progress on this image view. Returns false if the download in * progress deals with the same url. The download is not stopped in that * case. */ private static boolean cancelPotentialDownload(String url, ImageView imageView) { BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView); if (bitmapDownloaderTask != null) { String bitmapUrl = bitmapDownloaderTask.url; if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) { bitmapDownloaderTask.cancel(true); } else { // The same URL is already being downloaded. return false; } } return true; } /** * @param imageView * Any imageView * @return Retrieve the currently active download task (if any) associated * with this imageView. null if there is no such task. */ private static BitmapDownloaderTask getBitmapDownloaderTask(ImageView imageView) { if (imageView != null) { Drawable drawable = imageView.getDrawable(); if (drawable instanceof DownloadedDrawable) { DownloadedDrawable downloadedDrawable = (DownloadedDrawable) drawable; return downloadedDrawable.getBitmapDownloaderTask(); } } return null; } Bitmap downloadBitmap(String url) { final int IO_BUFFER_SIZE = 4 * 1024; File cacheFile = null; try { MessageDigest mDigest = MessageDigest.getInstance("SHA-1"); mDigest.update(url.getBytes()); final String cacheKey = bytesToHexString(mDigest.digest()); if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) { cacheFile = new File(Environment.getExternalStorageDirectory() + File.separator + "Android" + File.separator + "data" + File.separator + mContext.getPackageName() + File.separator + "cache" + File.separator + "bitmap_" + cacheKey + ".tmp"); } } catch (NoSuchAlgorithmException e) { // Oh well, SHA-1 not available (weird), don't cache bitmaps. } HttpGet getRequest = null; try { getRequest = new HttpGet(url); } catch (IllegalArgumentException e) { Log.e(TAG, "Error while constructing get request: " + e.getMessage()); return null; } try { HttpResponse response = mClient.execute(getRequest); final int statusCode = response.getStatusLine().getStatusCode(); if (statusCode != HttpStatus.SC_OK) { Log.w("ImageDownloader", "Error " + statusCode + " while retrieving bitmap from " + url); return null; } final HttpEntity entity = response.getEntity(); if (entity != null) { final byte[] respBytes = EntityUtils.toByteArray(entity); if (cacheFile != null) { try { cacheFile.getParentFile().mkdirs(); cacheFile.createNewFile(); FileOutputStream fos = new FileOutputStream(cacheFile); fos.write(respBytes); fos.close(); } catch (FileNotFoundException e) { Log.w(TAG, "Error writing to bitmap cache: " + cacheFile.toString(), e); } catch (IOException e) { Log.w(TAG, "Error writing to bitmap cache: " + cacheFile.toString(), e); } } return BitmapFactory.decodeByteArray(respBytes, 0, respBytes.length); } } catch (IOException e) { getRequest.abort(); Log.w(TAG, "I/O error while retrieving bitmap from " + url, e); } catch (IllegalStateException e) { getRequest.abort(); Log.w(TAG, "Incorrect URL: " + url); } catch (Exception e) { getRequest.abort(); Log.w(TAG, "Error while retrieving bitmap from " + url, e); } return null; } /** * The actual AsyncTask that will asynchronously download the image. */ class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { private String url; private final WeakReference<ImageView> imageViewReference; public BitmapDownloaderTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } /** * Actual download method. */ @Override protected Bitmap doInBackground(String... params) { url = params[0]; return downloadBitmap(url); } /** * Once the image is downloaded, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { if (isCancelled()) { bitmap = null; } addBitmapToCache(url, bitmap); if (bitmap != null && imageViewReference != null) { ImageView imageView = imageViewReference.get(); BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView); // Change bitmap only if this process is still associated with // it // Or if we don't use any bitmap to task association // (NO_DOWNLOADED_DRAWABLE mode) if (this == bitmapDownloaderTask) { ImageViewUtils.setBitmapWithFade(imageView, bitmap); } } } } /** * A fake Drawable that will be attached to the imageView while the download * is in progress. * * <p> * Contains a reference to the actual download task, so that a download task * can be stopped if a new binding is required, and makes sure that only the * last started download process can bind its result, independently of the * download finish order. * </p> */ static class DownloadedDrawable extends BitmapDrawable { private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference; public DownloadedDrawable(Context context, BitmapDownloaderTask bitmapDownloaderTask, int emptyResId) { super(BitmapFactory.decodeResource(context.getResources(), emptyResId)); bitmapDownloaderTaskReference = new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask); } public BitmapDownloaderTask getBitmapDownloaderTask() { return bitmapDownloaderTaskReference.get(); } } /* * Cache-related fields and methods. * * We use a hard and a soft cache. A soft reference cache is too * aggressively cleared by the Garbage Collector. */ private static final int HARD_CACHE_CAPACITY = 50; private static final int DELAY_BEFORE_PURGE = 10 * 1000; // in milliseconds // Hard cache, with a fixed maximum capacity and a life duration private final HashMap<String, Bitmap> sHardBitmapCache = new LinkedHashMap<String, Bitmap>( HARD_CACHE_CAPACITY / 2, 0.75f, true) { @Override protected boolean removeEldestEntry(LinkedHashMap.Entry<String, Bitmap> eldest) { if (size() > HARD_CACHE_CAPACITY) { // Entries push-out of hard reference cache are transferred to // soft reference cache sSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue())); return true; } else return false; } }; // Soft cache for bitmaps kicked out of hard cache private final static ConcurrentHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache = new ConcurrentHashMap<String, SoftReference<Bitmap>>( HARD_CACHE_CAPACITY / 2); private final Handler purgeHandler = new Handler(); private final Runnable purger = new Runnable() { public void run() { clearCache(); } }; /** * Adds this bitmap to the cache. * * @param bitmap * The newly downloaded bitmap. */ private void addBitmapToCache(String url, Bitmap bitmap) { if (bitmap != null) { synchronized (sHardBitmapCache) { sHardBitmapCache.put(url, bitmap); } } } /** * @param url * The URL of the image that will be retrieved from the cache. * @return The cached bitmap or null if it was not found. */ private Bitmap getBitmapFromCache(String url) { if (url != null) { // First try the hard reference cache synchronized (sHardBitmapCache) { final Bitmap bitmap = sHardBitmapCache.get(url); if (bitmap != null) { // Bitmap found in hard cache // Move element to first position, so that it is removed // last sHardBitmapCache.remove(url); sHardBitmapCache.put(url, bitmap); return bitmap; } } // Then try the soft reference cache SoftReference<Bitmap> bitmapReference = sSoftBitmapCache.get(url); if (bitmapReference != null) { final Bitmap bitmap = bitmapReference.get(); if (bitmap != null) { // Bitmap found in soft cache return bitmap; } else { // Soft reference has been Garbage Collected sSoftBitmapCache.remove(url); } } File cacheFile = null; try { MessageDigest mDigest = MessageDigest.getInstance("SHA-1"); mDigest.update(url.getBytes()); final String cacheKey = bytesToHexString(mDigest.digest()); if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) { cacheFile = new File(Environment.getExternalStorageDirectory() + File.separator + "Android" + File.separator + "data" + File.separator + mContext.getPackageName() + File.separator + "cache" + File.separator + "bitmap_" + cacheKey + ".tmp"); } } catch (NoSuchAlgorithmException e) { // Oh well, SHA-1 not available (weird), don't cache bitmaps. } if (cacheFile != null && cacheFile.exists()) { Bitmap cachedBitmap = BitmapFactory.decodeFile(cacheFile.toString()); if (cachedBitmap != null) { addBitmapToCache(url, cachedBitmap); return cachedBitmap; } } } return null; } /** * Clears the image cache used internally to improve performance. Note that * for memory efficiency reasons, the cache will automatically be cleared * after a certain inactivity delay. */ public void clearCache() { sHardBitmapCache.clear(); sSoftBitmapCache.clear(); } /** * Allow a new delay before the automatic cache clear is done. */ private void resetPurgeTimer() { purgeHandler.removeCallbacks(purger); purgeHandler.postDelayed(purger, DELAY_BEFORE_PURGE); } private static String bytesToHexString(byte[] bytes) { // http://stackoverflow.com/questions/332079 StringBuffer sb = new StringBuffer(); for (int i = 0; i < bytes.length; i++) { String hex = Integer.toHexString(0xFF & bytes[i]); if (hex.length() == 1) { sb.append('0'); } sb.append(hex); } return sb.toString(); } }