Android Open Source - aBusTripMK Open Street Map Tile Downloader

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License

The source code is released under:

GNU General Public License

Java Source Code

// Created by plusminus on 21:31:36 - 25.09.2008
package org.andnav.osm.services.util;
// ww w. j av  a 2 s . c o  m
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.UnknownHostException;

import org.andnav.osm.services.IOpenStreetMapTileProviderCallback;
import org.andnav.osm.views.util.OpenStreetMapRendererInfo;

import android.util.Log;

/**
 * The OpenStreetMapTileDownloader loads tiles from a server and passes them to
 * a OpenStreetMapTileFilesystemProvider.
 * @author Nicolas Gramlich
 * @author Manuel Stahl
 *
 */
public class OpenStreetMapTileDownloader extends OpenStreetMapAsyncTileProvider {
        // ===========================================================
        // Constants
        // ===========================================================

        private static final String DEBUGTAG = "OSM_DOWNLOADER";

        // ===========================================================
        // Fields
        // ===========================================================

        private final OpenStreetMapTileFilesystemProvider mMapTileFSProvider;

        // ===========================================================
        // Constructors
        // ===========================================================

        public OpenStreetMapTileDownloader(final OpenStreetMapTileFilesystemProvider aMapTileFSProvider){
                super(NUMBER_OF_TILE_DOWNLOAD_THREADS, TILE_DOWNLOAD_MAXIMUM_QUEUE_SIZE);
                this.mMapTileFSProvider = aMapTileFSProvider;
        }

        // ===========================================================
        // Getter & Setter
        // ===========================================================

        // ===========================================================
        // Methods from SuperClass/Interfaces
        // ===========================================================

        @Override
        protected String debugtag() {
                return DEBUGTAG;
        }

        @Override
        protected Runnable getTileLoader(IOpenStreetMapTileProviderCallback aCallback) {
                return new TileLoader(aCallback);
        };
        
        // ===========================================================
        // Methods
        // ===========================================================

        private String buildURL(final OpenStreetMapTile tile) {
                OpenStreetMapRendererInfo renderer = OpenStreetMapRendererInfo.values()[tile.rendererID];
                return renderer.getTileURLString(tile);
        }

        // ===========================================================
        // Inner and Anonymous Classes
        // ===========================================================
        
        private class TileLoader extends OpenStreetMapAsyncTileProvider.TileLoader {

                public TileLoader(final IOpenStreetMapTileProviderCallback aCallback) {
                        super(aCallback);
                }

                @Override
                public String loadTile(final OpenStreetMapTile aTile) throws CantContinueException {

                        InputStream in = null;
                        OutputStream out = null;

                        final File outputFile = mMapTileFSProvider.getOutputFile(aTile);
                        final String tileURLString = buildURL(aTile);
                        
                        try {
                                if(DEBUGMODE)
                                        Log.d(DEBUGTAG, "Downloading Maptile from url: " + tileURLString);

                                in = new BufferedInputStream(new URL(tileURLString).openStream(), StreamUtils.IO_BUFFER_SIZE);

                                final ByteArrayOutputStream dataStream = new ByteArrayOutputStream();
                                out = new BufferedOutputStream(dataStream, StreamUtils.IO_BUFFER_SIZE);
                                StreamUtils.copy(in, out);
                                out.flush();

                                final byte[] data = dataStream.toByteArray();
                                
                                // sanity check - don't save an empty file
                                if (data.length == 0) {
                                        Log.i(DEBUGTAG, "Empty maptile not saved: " + aTile);
                                } else {
                                        mMapTileFSProvider.saveFile(aTile, outputFile, data);
                                        if(DEBUGMODE)
                                                Log.d(DEBUGTAG, "Maptile saved " + data.length + " bytes : " + aTile);
                                }
                        } catch (final UnknownHostException e) {
                                // no network connection so empty the queue
                                Log.w(DEBUGTAG, "UnknownHostException downloading MapTile: " + aTile + " : " + e);
                                throw new CantContinueException();
                        } catch (final IOException e) {
                                Log.w(DEBUGTAG, "IOException downloading MapTile: " + aTile + " : " + e);
                        } catch(final Throwable e) {
                                Log.e(DEBUGTAG, "Error downloading MapTile: " + aTile, e);
                        } finally {
                                StreamUtils.closeStream(in);
                                StreamUtils.closeStream(out);
                        }

                        /* Don't immediately send the tile back.
                         * If we're moving, and the internet is a bit patchy, then by the time
                         * the download has finished we don't need this tile any more.
                         * If we still do need it then the file system provider will get it 
                         * again next time it's needed.
                         * That should be immediately because the view is redrawn when it
                         * receives this completion event.
                         */
                        return null;
                }
        };

}

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