Decrease Image downloading time with HttpURLConnection

Question

This is piece of code is using to download images. Can somebody tell me how to optimize this code to decrease download time for each image?

        URL url;
        HttpURLConnection connection = null;
        InputStream input = null;
        System.setProperty("http.keepAlive", "true");
        try {
            url = new URL(urlString);
            connection = (HttpURLConnection) url.openConnection();
            connection.setConnectTimeout(HTTP_CONNECTION_TIMEOUT);
            connection.setRequestProperty("Connection", "Keep-Alive");
            input = connection.getInputStream();
            return BitmapFactory.decodeStream(input);
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        } finally {
            currentRequestInProgress.remove(urlString);
            if (connection != null)
                connection.disconnect();
            if(input != null){
                try {
                    input.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }

Answer 1

Buffered streams usually result in greatly improved performance:

input = new BufferedInputStream(connection.getInputStream());

The buffer size is 8kb per default, tuning it may be an option (but not without measuring).

And, if you download multiple images: parallelize it with multiple threads (most of the time is consumed by I/O waits anyway), this usually improves performance by factors.

Answer 2

Resources:

You should really use try-with-resources:

URL url = new URL(urlstring);
System.setProperty("http.keepAlive","true");
try(HTTPUrlConnection connection = (HTTPUrlConnection) url.openConnection()){
    connection.setConnectTimeout(HTTP_CONNECTION_TIMEOUT);
    connection.setRequestProperty("Connection", "Keep-Alive");
    try(InputStream input = connection.getInputStream()){
       return BitmapFactory.decodeStream(input);
    }
    catch(IOException e){
       e.printStackTrace();
       return null;
    }
}
catch(MalformedURLException e){
    e.printStackTrace();
    return null;
}

This code should do exactly the same. The finally becomes useless, as try-with-resources does the job for you. Keep in mind, your resources should implement java.lang.AutoCloseable, this is required to use try-with-resources.

As mentioned in some comments:

Try-with-resources works only as of Android 4.4.

furthermore, if HTTPUrlConnection does not implement AutoCloseable you will have to restructure the code like this:

HTTPUrlConnection connection
try{
    connection = (HTTPUrlConnection) url.openConnection();
    //[...]
} 
catch(MalformedURLException e){
    e.printStackTrace();
    return null;
}
finally {
    if(connection != null)
        connection.disconnect();
}