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package tim.prune.function.srtm;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
/**
* High-resolution Srtm source, using 1-arcsecond data
* instead of the low-resolution 3-arcsecond data
* @author fperrin, activityworkshop
*/
public class SrtmHighResSource extends SrtmSource
{
/** Flag set to false if auth fails */
private boolean _enabled = true;
/** Auth string */
private final String _authString;
/** URL prefix for all tiles */
private static final String URL_PREFIX = "https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1.003/2000.02.11/";
/** Auth URL */
private static final String AUTH_HOST = "urs.earthdata.nasa.gov";
private static final int HTTP_CODE_OK = 200;
private static final int HTTP_CODE_REDIRECT = 302;
private static final int HTTP_CODE_NOTFOUND = 404;
/**
* @param inDiskPath disk path, if any
* @param inAuthString authentication string
*/
SrtmHighResSource(String inDiskPath, String inAuthString)
{
super(inDiskPath);
_authString = inAuthString;
}
@Override
public int getTilePixels() {
return 3601;
}
/**
* @return the Url for the given tile
*/
@Override
public URL getUrl(SrtmTile inTile)
{
URL url = null;
try {
url = new URL(URL_PREFIX + getFilename(inTile));
} catch (MalformedURLException e) {} // ignore error, url stays null
return url;
}
@Override
public Result downloadTile(SrtmTile inTile) throws SrtmAuthException
{
final String authString = getAuthString();
if (authString == null || !_enabled) {return Result.NOT_ENABLED;}
try
{
// Retrieve a stream for the resource
URL url = getUrl(inTile);
InputStream inStream = getResource(url, authString);
if (writeFileFromStream(url, inStream)) {
return Result.DOWNLOADED;
}
}
catch (SrtmAuthException authExc)
{
_enabled = false;
throw authExc;
}
catch (Exception e) {}
return Result.DOWNLOAD_FAILED;
}
@Override
public String getFilename(SrtmTile inTile)
{
return inTile.getTileName() + ".SRTMGL1.hgt.zip";
}
/**
* @return auth string, if possible
*/
private String getAuthString()
{
if (_authString == null) {
return null;
}
return "Basic " + _authString;
}
/**
* Returns an input stream for a designated resource on a URS
* authenticated remote server.
* @param resourceUrl url to get
* @param inAuthString username/password from config
*/
private static InputStream getResource(URL resourceUrl, String inAuthString)
throws Exception
{
// Method provided by:
// https://wiki.earthdata.nasa.gov/display/EL/How+To+Access+Data+With+Java
int redirects = 0;
URL url = resourceUrl;
// Place an upper limit on the number of redirects we will follow
while( redirects < 10 )
{
++redirects;
// Configure a connection to the resource server and submit the
// request for our resource.
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setInstanceFollowRedirects(false);
connection.setUseCaches(false);
connection.setDoInput(true);
// If this is the URS server, add in the authentication header.
if (url.getHost().startsWith(AUTH_HOST))
{
connection.setDoOutput(true);
connection.setRequestProperty("Authorization", inAuthString);
}
// Execute the request and get the response status code.
int status = connection.getResponseCode();
if (status == HTTP_CODE_OK)
{
// OK means that we have got our resource
return connection.getInputStream();
}
if (status == HTTP_CODE_REDIRECT)
{
// 302 is a redirect, so we go round the loop again.
url = new URL(connection.getHeaderField("Location"));
}
else if (status == HTTP_CODE_NOTFOUND) {
throw new Exception("SRTM file not found");
}
else {
throw new SrtmAuthException(status);
}
}
// If we get here, we exceeded our redirect limit
throw new Exception("Redirection limit exceeded");
}
}
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