Android Open Source - GreenDroid Image Loader

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (C) 2010 Cyril Mottier (http://www.cyrilmottier.com)
 *// w w w.j  a  v a2s .c o m
 * 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 greendroid.image;

import greendroid.util.Config;
import greendroid.util.GDUtils;

import java.io.InputStream;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;

import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.os.Process;
import android.text.TextUtils;
import android.util.DisplayMetrics;
import android.util.Log;

/**
 * An ImageLoader asynchronously loads image from a given url. Client may be
 * notified from the current image loading state using the
 * {@link ImageLoaderCallback}.
 * <p>
 * <em><strong>Note: </strong>You normally don't need to use the {@link ImageLoader}
 * class directly in your application. You'll generally prefer using an
 * {@link ImageRequest} that takes care of the entire loading process.</em>
 * </p>
 * 
 * @author Cyril Mottier
 */
public class ImageLoader {

    private static final String LOG_TAG = ImageLoader.class.getSimpleName();

    /**
     * @author Cyril Mottier
     */
    public static interface ImageLoaderCallback {

        void onImageLoadingStarted(ImageLoader loader);

        void onImageLoadingEnded(ImageLoader loader, Bitmap bitmap);

        void onImageLoadingFailed(ImageLoader loader, Throwable exception);
    }

    private static final int ON_START = 0x100;
    private static final int ON_FAIL = 0x101;
    private static final int ON_END = 0x102;
    
    private static ImageCache sImageCache;
    private static ExecutorService sExecutor;
    private static BitmapFactory.Options sDefaultOptions;
    private static AssetManager sAssetManager;

    public ImageLoader(Context context) {
        if (sImageCache == null) {
            sImageCache = GDUtils.getImageCache(context);
        }
        if (sExecutor == null) {
            sExecutor = GDUtils.getExecutor(context);
        }
        if (sDefaultOptions == null) {
          sDefaultOptions = new BitmapFactory.Options();
          sDefaultOptions.inDither = true;
          sDefaultOptions.inScaled = true;
          sDefaultOptions.inDensity = DisplayMetrics.DENSITY_MEDIUM;
          sDefaultOptions.inTargetDensity = context.getResources().getDisplayMetrics().densityDpi;
        }
        sAssetManager = context.getAssets();
    }

    public Future<?> loadImage(String url, ImageLoaderCallback callback) {
        return loadImage(url, callback, null);
    }

    public Future<?> loadImage(String url, ImageLoaderCallback callback, ImageProcessor bitmapProcessor) {
        return loadImage(url, callback, bitmapProcessor, null);
    }
    
    public Future<?> loadImage(String url, ImageLoaderCallback callback, ImageProcessor bitmapProcessor, BitmapFactory.Options options) {
        return sExecutor.submit(new ImageFetcher(url, callback, bitmapProcessor, options));
    }

    private class ImageFetcher implements Runnable {

        private String mUrl;
        private ImageHandler mHandler;
        private ImageProcessor mBitmapProcessor;
        private BitmapFactory.Options mOptions;

        public ImageFetcher(String url, ImageLoaderCallback callback, ImageProcessor bitmapProcessor, BitmapFactory.Options options) {
            mUrl = url;
            mHandler = new ImageHandler(url, callback);
            mBitmapProcessor = bitmapProcessor;
            mOptions = options;
        }

        public void run() {

            Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);

            final Handler h = mHandler;
            Bitmap bitmap = null;
            Throwable throwable = null;

            h.sendMessage(Message.obtain(h, ON_START));

            try {

                if (TextUtils.isEmpty(mUrl)) {
                    throw new Exception("The given URL cannot be null or empty");
                }
                
                InputStream inputStream = null;
                
                if (mUrl.startsWith("file:///android_asset/")) {
                    inputStream = sAssetManager.open(mUrl.replaceFirst("file:///android_asset/", ""));
                } else {
                    inputStream = new URL(mUrl).openStream();
                }

                // TODO Cyril: Use a AndroidHttpClient?
                bitmap = BitmapFactory.decodeStream(inputStream, null, (mOptions == null) ? sDefaultOptions : mOptions);
                
                if (mBitmapProcessor != null && bitmap != null) {
                    final Bitmap processedBitmap = mBitmapProcessor.processImage(bitmap);
                    if (processedBitmap != null) {
                        bitmap = processedBitmap;
                    }
                }

            } catch (Exception e) {
                // An error occured while retrieving the image
                if (Config.GD_ERROR_LOGS_ENABLED) {
                    Log.e(LOG_TAG, "Error while fetching image", e);
                }
                throwable = e;
            }

            if (bitmap == null) {
                if (throwable == null) {
                    // Skia returned a null bitmap ... that's usually because
                    // the given url wasn't pointing to a valid image
                    throwable = new Exception("Skia image decoding failed");
                }
                h.sendMessage(Message.obtain(h, ON_FAIL, throwable));
            } else {
                h.sendMessage(Message.obtain(h, ON_END, bitmap));
            }
        }
    }

    private class ImageHandler extends Handler {

        private String mUrl;
        private ImageLoaderCallback mCallback;

        private ImageHandler(String url, ImageLoaderCallback callback) {
            mUrl = url;
            mCallback = callback;
        }

        @Override
        public void handleMessage(Message msg) {

            switch (msg.what) {

                case ON_START:
                    if (mCallback != null) {
                        mCallback.onImageLoadingStarted(ImageLoader.this);
                    }
                    break;

                case ON_FAIL:
                    if (mCallback != null) {
                        mCallback.onImageLoadingFailed(ImageLoader.this, (Throwable) msg.obj);
                    }
                    break;

                case ON_END:

                    final Bitmap bitmap = (Bitmap) msg.obj;
                    sImageCache.put(mUrl, bitmap);

                    if (mCallback != null) {
                        mCallback.onImageLoadingEnded(ImageLoader.this, bitmap);
                    }
                    break;

                default:
                    super.handleMessage(msg);
                    break;
            }
        };
    }

}

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