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 codelovers.test.androidyoutubeplayer; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.HttpStatus; import org.apache.http.client.methods.HttpGet; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Color; import android.graphics.drawable.ColorDrawable; import android.graphics.drawable.Drawable; import android.net.http.AndroidHttpClient; import android.os.AsyncTask; import android.os.Handler; import android.util.Log; import android.widget.ImageView; import java.io.BufferedOutputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.lang.ref.SoftReference; import java.lang.ref.WeakReference; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.concurrent.ConcurrentHashMap; // From the XMLAdapters sample code. Really helpful. /** * 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 LOG_TAG = "ImageDownloader"; private static final int HARD_CACHE_CAPACITY = 40; private static final int DELAY_BEFORE_PURGE = 30 * 1000; // in milliseconds // Hard cache, with a fixed maximum capacity and a life duration private final HashMap<String, Bitmap> mHardBitmapCache = new LinkedHashMap<String, Bitmap>( HARD_CACHE_CAPACITY / 2, 0.75f, true) { private static final long serialVersionUID = 1L; @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 bitmap 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(); } }; /** * 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, null); } /** * Same as {@link #download(String, ImageView)}, with the possibility to * provide an additional cookie that will be used when the image will be * retrieved. * * @param url The URL of the image to download. * @param imageView The ImageView to bind the downloaded image to. * @param cookie A cookie String that will be used by the http connection. */ public void download(String url, ImageView imageView, String cookie) { resetPurgeTimer(); Bitmap bitmap = getBitmapFromCache(url); if (bitmap == null) { Log.i(LOG_TAG, LOG_TAG + ": Error retrieving bitmap from cache " + url.split("/")[4]); forceDownload(url, imageView, cookie); } 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, String cookie) { // 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(task); imageView.setImageDrawable(downloadedDrawable); task.execute(url, cookie); } } /** * 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() { mHardBitmapCache.clear(); sSoftBitmapCache.clear(); } private void resetPurgeTimer() { purgeHandler.removeCallbacks(purger); purgeHandler.postDelayed(purger, DELAY_BEFORE_PURGE); } /** * 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; } /** * @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 (mHardBitmapCache) { final Bitmap bitmap = mHardBitmapCache.get(url); if (bitmap != null) { // Bitmap found in hard cache // Move element to first position, so that it is removed last mHardBitmapCache.remove(url); mHardBitmapCache.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; } /** * The actual AsyncTask that will asynchronously download the image. */ class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { private static final int IO_BUFFER_SIZE = 4 * 1024; 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) { final AndroidHttpClient client = AndroidHttpClient.newInstance("Android"); url = params[0]; final HttpGet getRequest = new HttpGet(url); String cookie = params[1]; if (cookie != null) { getRequest.setHeader("cookie", cookie); } 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; OutputStream outputStream = null; try { inputStream = entity.getContent(); final ByteArrayOutputStream dataStream = new ByteArrayOutputStream(); outputStream = new BufferedOutputStream(dataStream, IO_BUFFER_SIZE); copy(inputStream, outputStream); outputStream.flush(); final byte[] data = dataStream.toByteArray(); final Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length); // FIXME : Should use NOTE FIXME was in the original // file. // BitmapFactory.decodeStream(inputStream) instead. // final Bitmap bitmap = // BitmapFactory.decodeStream(inputStream); return bitmap; } finally { if (inputStream != null) { inputStream.close(); } if (outputStream != null) { outputStream.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); } finally { if (client != null) { client.close(); } } return null; } /** * Once the image is downloaded, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { if (isCancelled()) { bitmap = null; } // Add bitmap to cache if (bitmap != null) { synchronized (mHardBitmapCache) { mHardBitmapCache.put(url, bitmap); } } if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView); // Change bitmap only if this process is still associated with // it if (this == bitmapDownloaderTask) { imageView.setImageBitmap(bitmap); } } } public void copy(InputStream in, OutputStream out) throws IOException { byte[] b = new byte[IO_BUFFER_SIZE]; int read; while ((read = in.read(b)) != -1) { out.write(b, 0, read); } } } /** * 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.BLACK); bitmapDownloaderTaskReference = new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask); } public BitmapDownloaderTask getBitmapDownloaderTask() { return bitmapDownloaderTaskReference.get(); } } }