public static byte[] getImage(int x, int y, int zoom, HttpMapSource mapSource)
      throws IOException, InterruptedException, UnrecoverableDownloadException {

    MapSpace mapSpace = mapSource.getMapSpace();
    int maxTileIndex = mapSpace.getMaxPixels(zoom) / mapSpace.getTileSize();
    if (x > maxTileIndex)
      throw new RuntimeException("Invalid tile index x=" + x + " for zoom " + zoom);
    if (y > maxTileIndex)
      throw new RuntimeException("Invalid tile index y=" + y + " for zoom " + zoom);

    TileStore ts = TileStore.getInstance();

    // Thread.sleep(2000);

    // Test code for creating random download failures
    // if (Math.random()>0.7) throw new
    // IOException("intentionally download error");

    Settings s = Settings.getInstance();

    TileStoreEntry tile = null;
    if (s.tileStoreEnabled) {

      // Copy the file from the persistent tilestore instead of
      // downloading it from internet.
      tile = ts.getTile(x, y, zoom, mapSource);
      boolean expired = isTileExpired(tile);
      if (tile != null) {
        if (expired) {
          log.trace("Expired: " + mapSource.getName() + " " + tile);
        } else {
          log.trace("Tile of map source " + mapSource.getName() + " used from tilestore");
          byte[] data = tile.getData();
          notifyCachedTileUsed(data.length);
          return data;
        }
      }
    }
    byte[] data = null;
    if (tile == null) {
      data = downloadTileAndUpdateStore(x, y, zoom, mapSource);
      notifyTileDownloaded(data.length);
    } else {
      byte[] updatedData = updateStoredTile(tile, mapSource);
      if (updatedData != null) {
        data = updatedData;
        notifyTileDownloaded(data.length);
      } else {
        data = tile.getData();
        notifyCachedTileUsed(data.length);
      }
    }
    return data;
  }
  public static byte[] updateStoredTile(TileStoreEntry tile, HttpMapSource mapSource)
      throws UnrecoverableDownloadException, IOException, InterruptedException {
    final int x = tile.getX();
    final int y = tile.getY();
    final int zoom = tile.getZoom();
    final HttpMapSource.TileUpdate tileUpdate = mapSource.getTileUpdate();

    switch (tileUpdate) {
      case ETag:
        {
          boolean unchanged = hasTileETag(tile, mapSource);
          if (unchanged) {
            if (log.isTraceEnabled())
              log.trace("Data unchanged on server (eTag): " + mapSource + " " + tile);
            return null;
          }
          break;
        }
      case LastModified:
        {
          boolean isNewer = isTileNewer(tile, mapSource);
          if (!isNewer) {
            if (log.isTraceEnabled())
              log.trace("Data unchanged on server (LastModified): " + mapSource + " " + tile);
            return null;
          }
          break;
        }
    }
    HttpURLConnection conn = mapSource.getTileUrlConnection(zoom, x, y);
    if (conn == null)
      throw new UnrecoverableDownloadException(
          "Tile x="
              + x
              + " y="
              + y
              + " zoom="
              + zoom
              + " is not a valid tile in map source "
              + mapSource);

    if (log.isTraceEnabled()) log.trace(String.format("Checking %s %s", mapSource.getName(), tile));

    prepareConnection(conn);

    boolean conditionalRequest = false;

    switch (tileUpdate) {
      case IfNoneMatch:
        {
          if (tile.geteTag() != null) {
            conn.setRequestProperty("If-None-Match", tile.geteTag());
            conditionalRequest = true;
          }
          break;
        }
      case IfModifiedSince:
        {
          if (tile.getTimeLastModified() > 0) {
            conn.setIfModifiedSince(tile.getTimeLastModified());
            conditionalRequest = true;
          }
          break;
        }
    }

    conn.connect();

    Settings s = Settings.getInstance();

    int code = conn.getResponseCode();

    if (conditionalRequest && code == HttpURLConnection.HTTP_NOT_MODIFIED) {
      // Data unchanged on server
      if (s.tileStoreEnabled) {
        tile.update(conn.getExpiration());
        TileStore.getInstance().putTile(tile, mapSource);
      }
      if (log.isTraceEnabled()) log.trace("Data unchanged on server: " + mapSource + " " + tile);
      return null;
    }
    byte[] data = loadBodyDataInBuffer(conn);

    if (code != HttpURLConnection.HTTP_OK) throw new DownloadFailedException(conn, code);

    checkContentType(conn, data);
    checkContentLength(conn, data);

    String eTag = conn.getHeaderField("ETag");
    long timeLastModified = conn.getLastModified();
    long timeExpires = conn.getExpiration();

    Utilities.checkForInterruption();
    TileImageType imageType = Utilities.getImageType(data);
    if (imageType == null)
      throw new UnrecoverableDownloadException("The returned image is of unknown format");
    if (s.tileStoreEnabled) {
      TileStore.getInstance()
          .putTileData(data, x, y, zoom, mapSource, timeLastModified, timeExpires, eTag);
    }
    Utilities.checkForInterruption();
    return data;
  }