src/tim/prune/function/srtm/TileDownloader.java

   1 package tim.prune.function.srtm;
   2
   3 import java.io.File;
   4 import java.io.FileOutputStream;
   5 import java.io.IOException;
   6 import java.io.InputStream;
   7 import java.net.URL;
   8 import java.net.URLConnection;
   9
  10 import tim.prune.GpsPrune;
  11 import tim.prune.config.Config;
  12
  13 /**
  14  * Class to provide a download function for the Space Shuttle's SRTM data files.
  15  * HGT files are downloaded into memory via HTTP and stored in the map cache.
  16  */
  17 public class TileDownloader
  18 {
  19         /** Possible results of the download */
  20         public enum Result {DOWNLOADED, NOTHING_TO_DO, DOWNLOAD_FAILED, CACHE_FAILED};
  21
  22         /**
  23          * Download a single tile of SRTM data
  24          * @param inUrl remote URL to get
  25          */
  26         public Result downloadTile(URL inUrl)
  27         {
  28                 if (inUrl == null) {
  29                         return Result.NOTHING_TO_DO;
  30                 }
  31
  32                 // Check the cache is ok
  33                 final String diskCachePath = Config.getConfigString(Config.KEY_DISK_CACHE);
  34                 if (diskCachePath != null)
  35                 {
  36                         File srtmDir = new File(diskCachePath, "srtm");
  37                         if (srtmDir.exists() && !srtmDir.isDirectory()) {
  38                                 // exists but isn't a directory - can't be used
  39                                 return Result.CACHE_FAILED;
  40                         }
  41                         if (!srtmDir.exists() && !srtmDir.mkdir()) {
  42                                 // can't create the srtm directory
  43                                 return Result.CACHE_FAILED;
  44                         }
  45                 }
  46                 else {
  47                         // no cache set up
  48                         return Result.CACHE_FAILED;
  49                 }
  50
  51                 // Define streams
  52                 FileOutputStream outStream = null;
  53                 InputStream inStream = null;
  54                 Result result = Result.NOTHING_TO_DO;
  55                 try
  56                 {
  57                         // See if we've already got this tile or not
  58                         File outputFile = getFileToWrite(inUrl);
  59                         if (outputFile != null)
  60                         {
  61                                 System.out.println("Download: Need to download: " + inUrl);
  62                                 outStream = new FileOutputStream(outputFile);
  63                                 URLConnection conn = inUrl.openConnection();
  64                                 conn.setRequestProperty("User-Agent", "GpsPrune v" + GpsPrune.VERSION_NUMBER);
  65                                 inStream = conn.getInputStream();
  66                                 // Copy all the bytes to the file
  67                                 int c;
  68                                 while ((c = inStream.read()) != -1)
  69                                 {
  70                                         outStream.write(c);
  71                                 }
  72                                 result = Result.DOWNLOADED;
  73                         }
  74                 }
  75                 catch (IOException ioe) {
  76                         System.err.println(ioe.getClass().getName() + " - " + ioe.getMessage());
  77                         result = Result.DOWNLOAD_FAILED;
  78                 }
  79                 // Make sure streams are closed
  80                 try {inStream.close();} catch (Exception e) {}
  81                 try {outStream.close();} catch (Exception e) {}
  82
  83                 return result;
  84         }
  85
  86         /**
  87          * See whether the SRTM file is already available locally
  88          * @param inUrl URL for online resource
  89          * @return file object to write to, or null if already there
  90          */
  91         private static File getFileToWrite(URL inUrl)
  92         {
  93                 String diskCachePath = Config.getConfigString(Config.KEY_DISK_CACHE);
  94                 if (diskCachePath != null)
  95                 {
  96                         File srtmDir = new File(diskCachePath, "srtm");
  97                         if (srtmDir.exists() && srtmDir.isDirectory() && srtmDir.canRead())
  98                         {
  99                                 File srtmFile = new File(srtmDir, new File(inUrl.getFile()).getName());
 100                                 if (!srtmFile.exists() || !srtmFile.canRead() || srtmFile.length() <= 400) {
 101                                         return srtmFile;
 102                                 }
 103                         }
 104                 }
 105                 return null;
 106         }
 107 }