Java tutorial
/* * Copyright (C) 2010 The Android Open Source Project * * 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 com.battlelancer.seriesguide.util; 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.impl.client.DefaultHttpClient; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Bitmap.CompressFormat; import android.graphics.BitmapFactory; import android.graphics.Color; import android.graphics.drawable.ColorDrawable; 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; import java.io.File; import java.io.FileOutputStream; import java.io.FilterInputStream; import java.io.IOException; import java.io.InputStream; import java.lang.ref.SoftReference; import java.lang.ref.WeakReference; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.concurrent.ConcurrentHashMap; /** * From http://code.google.com/p/android-imagedownloader. This helper class * download images from the Internet and binds those with the provided * ImageView. A local cache of downloaded images is maintained internally to * improve performance. */ public class ImageDownloader { private static final String LOG_TAG = "ImageDownloader"; private static ImageDownloader _instance; private String mDiskCacheDir; private ImageDownloader(Context context) { // TODO replace with getExternalFilesDir (but can be null!) once we are // min API level 8 mDiskCacheDir = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Android/data/" + context.getPackageName() + "/files"; } public static synchronized ImageDownloader getInstance(Context context) { if (_instance == null) { _instance = new ImageDownloader(context); } return _instance; } /** * 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. */ public void download(String url, ImageView imageView) { download(url, imageView, true); } /** * 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 isDiskCaching Wether to cache the image to disk or just memory. */ public void download(String url, ImageView imageView, boolean isDiskCaching) { resetPurgeTimer(); Bitmap bitmap = getBitmapFromCache(url); if (bitmap == null) { forceDownload(url, imageView, isDiskCaching); } 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, boolean isDiskCaching) { // 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, isDiskCaching); DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task); imageView.setImageDrawable(downloadedDrawable); 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, boolean isDiskCaching) { File imagefile = null; if (isDiskCaching) { String filename = Integer.toHexString(url.hashCode()) + "." + CompressFormat.JPEG.name(); imagefile = new File(mDiskCacheDir + "/" + filename); if (Utils.isExtStorageAvailable()) { // try to get bitmap from disk cache first if (imagefile.exists()) { // disk cache hit final Bitmap bitmap = BitmapFactory.decodeFile(imagefile.getAbsolutePath()); if (bitmap != null) { return bitmap; } } } } // if loading from disk fails, download it final HttpClient client = new DefaultHttpClient(); final HttpGet getRequest = new HttpGet(url); try { HttpResponse response = client.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) { InputStream inputStream = null; try { inputStream = entity.getContent(); // return BitmapFactory.decodeStream(inputStream); // Bug on slow connections, fixed in future release. // Bitmap bitmap = BitmapFactory.decodeStream(new // FlushedInputStream(inputStream)); // write directly to disk Bitmap bitmap; if (isDiskCaching && Utils.isExtStorageAvailable()) { FileOutputStream outputstream = new FileOutputStream(imagefile); Utils.copy(new FlushedInputStream(inputStream), outputstream); outputstream.close(); bitmap = BitmapFactory.decodeFile(imagefile.getAbsolutePath()); } else { // if we have no external storage, decode directly bitmap = BitmapFactory.decodeStream(new FlushedInputStream(inputStream)); } // // TODO look if we can return the bitmap first, then save // in // // the background // if (Utils.isExtStorageAvailable()) { // // write the bitmap to the disk cache // FileOutputStream os = new FileOutputStream(imagefile); // // @SuppressWarnings("unused") // boolean isreconstructable = // bitmap.compress(CompressFormat.JPEG, 90, os); // os.close(); // } return bitmap; } finally { if (inputStream != null) { inputStream.close(); } entity.consumeContent(); } } } catch (IOException e) { getRequest.abort(); Log.w(LOG_TAG, "I/O error while retrieving bitmap from " + url, e); } catch (IllegalStateException e) { getRequest.abort(); Log.w(LOG_TAG, "Incorrect URL: " + url); } catch (Exception e) { getRequest.abort(); Log.w(LOG_TAG, "Error while retrieving bitmap from " + url, e); } return null; } /* * An InputStream that skips the exact number of bytes provided, unless it * reaches EOF. */ static class FlushedInputStream extends FilterInputStream { public FlushedInputStream(InputStream inputStream) { super(inputStream); } @Override public long skip(long n) throws IOException { long totalBytesSkipped = 0L; while (totalBytesSkipped < n) { long bytesSkipped = in.skip(n - totalBytesSkipped); if (bytesSkipped == 0L) { int b = read(); if (b < 0) { break; // we reached EOF } else { bytesSkipped = 1; // we read one byte } } totalBytesSkipped += bytesSkipped; } return totalBytesSkipped; } } /** * The actual AsyncTask that will asynchronously download the image. */ class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { private String url; private final WeakReference<ImageView> imageViewReference; private final boolean mIsDiskCaching; public BitmapDownloaderTask(ImageView imageView, boolean isDiskCaching) { imageViewReference = new WeakReference<ImageView>(imageView); mIsDiskCaching = isDiskCaching; } /** * Actual download method. */ @Override protected Bitmap doInBackground(String... params) { url = params[0]; return downloadBitmap(url, mIsDiskCaching); } /** * Once the image is downloaded, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { if (isCancelled()) { bitmap = null; } addBitmapToCache(url, bitmap); if (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) { imageView.setImageBitmap(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 ColorDrawable { private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference; public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) { super(Color.TRANSPARENT); 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 = 10; private static final int DELAY_BEFORE_PURGE = 5 * 1000; // in milliseconds // Hard cache, with a fixed maximum capacity and a life duration @SuppressWarnings("serial") 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) { // 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); } } 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); } }