better error handling for file loader

source/net/yacy/repository/LoaderDispatcher.java

@@ -266,11 +266,24 @@ public final class LoaderDispatcher {
 
         // load resource from the internet
         Response response = null;
-        if ((protocol.equals("http") || (protocol.equals("https")))) response = this.httpLoader.load(request, maxFileSize, checkBlacklist);
-        if (protocol.equals("ftp")) response = this.ftpLoader.load(request, true);
-        if (protocol.equals("smb")) response = this.smbLoader.load(request, true);
-        if (protocol.equals("file")) response = this.fileLoader.load(request, true);
-        if (response != null && response.getContent() != null) {
+        if (protocol.equals("http") || protocol.equals("https")) {
+            response = this.httpLoader.load(request, maxFileSize, checkBlacklist);
+        } else if (protocol.equals("ftp")) {
+            response = this.ftpLoader.load(request, true);
+        } else if (protocol.equals("smb")) {
+            response = this.smbLoader.load(request, true);
+        } else if (protocol.equals("file")) {
+            response = this.fileLoader.load(request, true);
+        } else {
+            throw new IOException("Unsupported protocol '" + protocol + "' in url " + url);
+        }
+        if (response == null) {
+            throw new IOException("no response (NULL) for url " + url);
+        }
+        if (response.getContent() == null) {
+            throw new IOException("empty response (code " + response.getStatus() + ") for url " + url);
+        }
+        
         // we got something. Now check if we want to store that to the cache
         // first check looks if we want to store the content to the cache
         if (crawlProfile == null || !crawlProfile.storeHTCache()) {
@@ -291,9 +304,6 @@ public final class LoaderDispatcher {
         return response;
     }
 
-        throw new IOException("Unsupported protocol '" + protocol + "' in url " + url);
-    }
-
     private int protocolMaxFileSize(final DigestURI url) {
     	if (url.isHTTP() || url.isHTTPS())
     		return this.sb.getConfigInt("crawler.http.maxFileSize", HTTPLoader.DEFAULT_MAXFILESIZE);
@@ -407,6 +417,7 @@ public final class LoaderDispatcher {
             this.cacheStrategy = cacheStrategy;
         }
 
+        @Override
         public void run() {
             if (this.cache != null && this.cache.exists()) return;
             try {