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.slava.android.utils; import android.content.Context; import android.content.res.Resources; 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.Handler; import android.util.Log; import android.widget.ImageView; import com.slava.android.R; 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 java.io.File; 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; /** * 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.class.getSimpleName(); private final Context mContext; private final Bitmap mLoadingIndicator; private final Bitmap mErrorIndicator; private ExternalCache mExternalCache; public ImageDownloader(Context appContext) { mContext = appContext; mLoadingIndicator = ((BitmapDrawable) appContext.getResources().getDrawable(R.drawable.ic_loading)) .getBitmap(); mErrorIndicator = ((BitmapDrawable) appContext.getResources().getDrawable(R.drawable.ic_error)).getBitmap(); mExternalCache = new ExternalCache(appContext); } /** * 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, int cornersRadius) { resetPurgeTimer(); // Get image from hash map if it is there Bitmap bitmap = getBitmapFromCache(url); if (bitmap == null) { File file = mExternalCache.checkExternalCache(url); if (file != null) { // Image is in external cache externalDownload(url, imageView, cornersRadius, file); } else { // Image must be downloaded from server forceDownload(url, imageView, cornersRadius); } } else { // Image is in hash map 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 cornersRadius) { // State sanity: url is guaranteed to never be null in // DownloadedDrawable and cache keys. if (url == null || url.equals("")) { imageView.setImageDrawable(null); return; } if (cancelPotentialDownload(url, imageView)) { BitmapDownloaderTask task = new BitmapDownloaderTask(imageView, cornersRadius); DownloadedDrawable downloadedDrawable = new DownloadedDrawable(imageView.getResources(), mLoadingIndicator, task); 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; // 4 KB // AndroidHttpClient is not allowed to be used from the main thread final HttpClient client = new DefaultHttpClient(); final HttpGet getRequest; try { getRequest = new HttpGet(url); } catch (IllegalArgumentException e) { Log.e(TAG, "download(): url = " + url, e); return null; // mErrorIndicator; } 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. return BitmapFactory.decodeStream(new FlushedInputStream(inputStream)); } finally { if (inputStream != null) { inputStream.close(); } entity.consumeContent(); } } } 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; //mErrorIndicator; } /* * 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 int mRoundCorners; public BitmapDownloaderTask(ImageView imageView, int roundCorners) { imageViewReference = new WeakReference<ImageView>(imageView); mRoundCorners = roundCorners; } /** * 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) { // Set the error default avatar image if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); imageView.setImageBitmap(mErrorIndicator); } return; } Bitmap result = bitmap;//ImageUtilities.getRoundedCornerBitmap(bitmap, mRoundCorners); addBitmapToCache(url, result); // Add the bitmap to the external cache as well mExternalCache.addBitmapToExternalCache(url, result); 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) { // Set the avatar image imageView.setImageBitmap(result); } } } } /** * 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(Resources res, Bitmap placeHolder, BitmapDownloaderTask bitmapDownloaderTask) { super(res, placeHolder); 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 = 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(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); } private void externalDownload(String url, ImageView imageView, int cornersRadius, File file) { ExternalDownloaderTask task = new ExternalDownloaderTask(imageView, cornersRadius, url); task.execute(file.toString()); imageView.setImageBitmap(mLoadingIndicator); } /** * The actual AsyncTask that will asynchronously download the image. */ class ExternalDownloaderTask extends AsyncTask<String, Void, Bitmap> { private String file; private final WeakReference<ImageView> imageViewReference; private final int mRoundCorners; private final String mUrl; public ExternalDownloaderTask(ImageView imageView, int roundCorners, String url) { imageViewReference = new WeakReference<ImageView>(imageView); mRoundCorners = roundCorners; mUrl = url; } /** * Actual download method. */ @Override protected Bitmap doInBackground(String... params) { file = params[0]; return BitmapFactory.decodeFile(file); } /** * Once the image is downloaded, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { if (bitmap == null) { // Set the error default avatar image if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); imageView.setImageBitmap(mErrorIndicator); } return; } addBitmapToCache(mUrl, bitmap); if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); if (imageView != null) { // Set the avatar image imageView.setImageBitmap(bitmap); } } } } }