Acync simple file downloader

Downloader.java

package com.nalabjp.android;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;

import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;

public class Downloader extends AsyncTask<String, Integer, File>{
	private static final String LOG_TAG = "Downloader";
	private boolean mIsNowDownloding = false;
	private Throwable mThrowable;
	private CallbackListener mListener;
	public static interface CallbackListener {
		public void onPreExecute();
		public void onProgressUpdate(Integer... progress);
		public void onPostExecute(File file);
		public void onCancelled(File file);
		public void onCatchException(Throwable t);
	}
	
	public void setCallbackListener(CallbackListener l) {
		mListener = l;
	}
	
	@Override
	protected File doInBackground(String... params) {
		File file = null;
		try {
			final URL url = new URL(params[0]);
			final URLConnection conn = url.openConnection();
			final InputStream in = conn.getInputStream();
			Map<String, List<String>> headers = conn.getHeaderFields();
			String contentDisposition = headers.get("Content-Disposition").get(0);
			String fileName = contentDisposition.substring(contentDisposition.indexOf("filename=")+"filename=".length()).replaceAll("\"", "");
			if (params.length > 1 && null != params[1] && 0 != params[1].length()) {
				file = new File(params[1], fileName);
			} else {
				file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), fileName);
			}
			try {
				final OutputStream out = new FileOutputStream(file, true);
				try {
					final int length = conn.getContentLength();
					final byte[] bytes = new byte[4096];
					float loaded = 0;
					float nowload = 0;
					mIsNowDownloding = true;
					while(!Thread.interrupted()){
					    int ret = in.read(bytes);
					    if(ret <= 0) {
					    	break;
					    }
					    out.write(bytes, 0, ret);
					    
					    nowload = loaded + ret;
					    loaded += ret;
					    publishProgress(Integer.valueOf((int)(nowload/length*100)));
					}
				} finally {
					mIsNowDownloding = false;
					out.close();
				}
			} finally {
				in.close();
			}
		} catch (Throwable t) {
			Log.e(LOG_TAG, "Uncaught exception is occured in progress download.", t);
			mThrowable = t;
		}
			
		return file;
	}
	
	@Override
	protected void onPreExecute() {
		if (mListener != null) {
			mListener.onPreExecute();
		}
	}
	
	@Override
	protected void onProgressUpdate(final Integer... progress) {
		if (mListener != null) {
			mListener.onProgressUpdate(progress);
		}
        }

	@Override
	protected void onPostExecute(File result) {
		if (mThrowable != null) {
			if (mListener != null) {
				mListener.onCatchException(mThrowable);
			}
			return;
		}
		if (isCancelled()) {
			return;
		}
		if (result != null && mListener != null) {
			mListener.onPostExecute(result);
		}
		
		mIsNowDownloding = false;
		result = null;
	}
	
	@Override
	protected void onCancelled(File result) {
		if (mIsNowDownloding && (result != null) && result.exists()) {
			result.delete();
		}
		
		if (mListener != null) {
			mListener.onCancelled(result);
		}
		
		mIsNowDownloding = false;
		result = null;
	}
	
}