BitmapManager.java

package org.sparkleshare.android.utils;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public enum BitmapManager {

INSTANCE;
	
	private final Map<String, SoftReference<Bitmap>> cache;
	private final ExecutorService pool;
	private Map<ImageView, String> imageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
	private Bitmap placeHolder;
	
	BitmapManager() {
		cache = new HashMap<String, SoftReference<Bitmap>>();
		pool = Executors.newFixedThreadPool(5);
	}
	
	public void setPlaceHolder(Bitmap bmp) {
		placeHolder = bmp;
	}
	
	public Bitmap getBitmapFromCache(String url) {
		if (cache.containsKey(url)) {
			return cache.get(url).get();
		}
		return null;
	}
	
	public void queueJob(final String url, final ImageView imageView,
			final int width, final int height) {
		/* Create handler in UI thread. */
		final Handler handler = new Handler() {
			@Override
			public void handleMessage(Message msg) {
				String tag = imageViews.get(imageView);
				if (tag != null && tag.equals(url)) {
					if (msg.obj != null) {
						imageView.setImageBitmap((Bitmap) msg.obj);
					} else {
						imageView.setImageBitmap(placeHolder);
						Log.d("BitmapManager", "fail " + url);
					}
				}
			}
		};

		pool.submit(new Runnable() {
			@Override
			public void run() {
				final Bitmap bmp = downloadBitmap(url, width, height);
				Message message = Message.obtain();
				message.obj = bmp;
				Log.d(null, "Item downloaded: " + url);

				handler.sendMessage(message);
			}
		});
	}
	
	public void loadBitmap(final String url, final ImageView imageView,
			final int width, final int height) {
		imageViews.put(imageView, url);
		Bitmap bitmap = getBitmapFromCache(url);

		// will be checked in UI thread causing no concurrency issues
		if (bitmap != null) {
			Log.d(null, "Item loaded from cache: " + url);
			imageView.setImageBitmap(bitmap);
		} else {
			imageView.setImageBitmap(placeHolder);
			queueJob(url, imageView, width, height);
		}
	}
	
	private Bitmap downloadBitmap(String url, int width, int height) {
		try {
			Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL(
					url).getContent());
			bitmap = Bitmap.createScaledBitmap(bitmap, width, height, true);
			cache.put(url, new SoftReference<Bitmap>(bitmap));
			return bitmap;
		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}

		return null;
	}
}