add ing ivalid url rejects with proper error

Closes #1723 (closed)

rest-api/src/main/java/lcsb/mapviewer/api/genomics/ReferenceGenomeController.java

 package lcsb.mapviewer.api.genomics;
 
 import java.io.IOException;
+import java.net.HttpURLConnection;
 import java.net.URISyntaxException;
+import java.net.URL;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.LinkedHashSet;
@@ -13,6 +15,7 @@ import javax.validation.constraints.NotNull;
 
 import org.hibernate.validator.constraints.NotEmpty;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.security.access.prepost.PreAuthorize;
 import org.springframework.validation.annotation.Validated;
@@ -230,6 +233,19 @@ public class ReferenceGenomeController extends BaseController {
       if (!url.toLowerCase().endsWith("bb")) {
         throw new QueryException("Only big bed format files are supported but found: \"" + url + "\".");
       }
+      if (url.startsWith("http")) {
+        try {
+          HttpURLConnection huc = (HttpURLConnection) new URL(url).openConnection();
+          huc.setRequestMethod("HEAD");
+          HttpStatus status = HttpStatus.valueOf(huc.getResponseCode());
+          if (status != HttpStatus.OK) {
+            throw new QueryException("Invalid url. Server returned: " + status.name() + " (" + status.value() + ").");
+          }
+        } catch (IOException e) {
+          throw new QueryException("Problem with processing url.", e);
+        }
+
+      }
 
       referenceGenomeService.addReferenceGenomeGeneMapping(genome, name, url);
       return new HashMap<>();