Java tutorial
package edu.mit.mobile.android.net; /* * Copyright (C) 2012-2013 MIT Mobile Experience Lab * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation version 2 * of the License. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ import java.io.BufferedInputStream; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.net.HttpURLConnection; import java.net.URL; import org.apache.http.HttpStatus; import android.content.Context; import android.net.ConnectivityManager; import android.net.NetworkInfo; import android.net.Uri; import android.support.v4.content.AsyncTaskLoader; import android.util.Log; import edu.mit.mobile.android.flipr.BuildConfig; import edu.mit.mobile.android.flipr.R; import edu.mit.mobile.android.locast.Constants; import edu.mit.mobile.android.locast.net.NetworkProtocolException; import edu.mit.mobile.android.utils.StreamUtils; public class DownloadLoader extends AsyncTaskLoader<Uri> { public static final String TAG = DownloadLoader.class.getSimpleName(); /** * Videos smaller than this will be presumed corrupted. */ private static final long MINIMUM_REASONABLE_VIDEO_SIZE = 1024; // bytes Exception mException; private final String mUrl; private final File outdir; private final ConnectivityManager mCm; public DownloadLoader(Context context, String url, File destinationDir) { super(context); mUrl = url; outdir = destinationDir; mCm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE); } @Override protected void onStartLoading() { super.onStartLoading(); forceLoad(); } public Exception getException() { return mException; } @Override public Uri loadInBackground() { boolean alreadyHasDownload = false; if (!outdir.exists() && !outdir.mkdirs()) { mException = new IOException("could not mkdirs: " + outdir.getAbsolutePath()); return null; } final String fname = mUrl.substring(mUrl.lastIndexOf('/')); final File outfile = new File(outdir, fname); alreadyHasDownload = outfile.exists() && outfile.length() > MINIMUM_REASONABLE_VIDEO_SIZE; final long lastModified = outfile.exists() ? outfile.lastModified() : 0; try { final NetworkInfo netInfo = mCm.getActiveNetworkInfo(); if (netInfo == null || !netInfo.isConnected()) { // no connection, but there's already a file. Hopefully it works! if (alreadyHasDownload) { return Uri.fromFile(outfile); } else { mException = new IOException(getContext().getString(R.string.err_no_data_connection)); return null; } } HttpURLConnection hc = (HttpURLConnection) new URL(mUrl).openConnection(); hc.setInstanceFollowRedirects(true); if (lastModified != 0) { hc.setIfModifiedSince(lastModified); } int resp = hc.getResponseCode(); if (resp >= 300 && resp < 400) { final String redirectUrl = hc.getURL().toExternalForm(); if (BuildConfig.DEBUG) { Log.d(TAG, "following redirect to " + redirectUrl); } hc = (HttpURLConnection) new URL(redirectUrl).openConnection(); if (lastModified != 0) { hc.setIfModifiedSince(lastModified); } resp = hc.getResponseCode(); } if (resp != HttpStatus.SC_OK && resp != HttpStatus.SC_NOT_MODIFIED) { Log.e(TAG, "got a non-200 response from server"); mException = new NetworkProtocolException("Received " + resp + " response from server"); return null; } if (resp == HttpStatus.SC_NOT_MODIFIED) { if (Constants.DEBUG) { Log.d(TAG, "got NOT MODIFIED"); } // verify the integrity of the file if (alreadyHasDownload) { if (Constants.DEBUG) { Log.d(TAG, fname + " has not been modified since it was downloaded last"); } return Uri.fromFile(outfile); } else { // re-request without the if-modified header. This shouldn't happen. hc = (HttpURLConnection) new URL(mUrl).openConnection(); final int responseCode = hc.getResponseCode(); if (responseCode != HttpStatus.SC_OK) { Log.e(TAG, "got a non-200 response from server"); mException = new NetworkProtocolException( "Received " + responseCode + " response from server"); return null; } } } final int contentLength = hc.getContentLength(); if (contentLength == 0) { Log.e(TAG, "got an empty response from server"); mException = new IOException("Received an empty response from server."); return null; } else if (contentLength < MINIMUM_REASONABLE_VIDEO_SIZE) { // this is probably not a // video Log.e(TAG, "got a very small response from server of length " + hc.getContentLength()); mException = new IOException("Received an unusually-small response from server."); return null; } boolean downloadSucceeded = false; try { final BufferedInputStream bis = new BufferedInputStream(hc.getInputStream()); final FileOutputStream fos = new FileOutputStream(outfile); if (Constants.DEBUG) { Log.d(TAG, "downloading..."); } StreamUtils.inputStreamToOutputStream(bis, fos); fos.close(); // store the server's last modified date in the filesystem outfile.setLastModified(hc.getLastModified()); downloadSucceeded = true; if (Constants.DEBUG) { Log.d(TAG, "done! Saved to " + outfile); } return Uri.fromFile(outfile); } finally { hc.disconnect(); // cleanup if this is the first attempt to download if (!alreadyHasDownload && !downloadSucceeded) { outfile.delete(); } } } catch (final IOException e) { Log.e(TAG, "error downloading file", e); mException = e; return null; } } }