Fix the issue of not being able to import the JSON format export of Solr index due to the inconsistency in time format between the exported JSON format and the Solr time format.

source/net/yacy/cora/federate/solr/responsewriter/FlatJSONResponseWriter.java

@@ -22,6 +22,7 @@ package net.yacy.cora.federate.solr.responsewriter;
 
 import java.io.IOException;
 import java.io.Writer;
+import java.text.SimpleDateFormat;
 import java.util.Collection;
 import java.util.Date;
 import java.util.List;
@@ -152,10 +153,11 @@ public class FlatJSONResponseWriter implements QueryResponseWriter, EmbeddedSolr
             json.put(name, Double.parseDouble(value));
         }
     }
-    
+
     public static final void writeDoc(final Writer writer, final SolrDocument doc) throws IOException {
         JSONObject json = new JSONObject();
         final Map<String, Object> fields = doc.getFieldValueMap();
+        SimpleDateFormat sdf=new SimpleDateFormat("YYYY-MM-DD'T'hh:mm:ssZ");
         for (String key: fields.keySet()) {
             if (key == null)  continue;
             Object value = doc.get(key);
@@ -165,15 +167,16 @@ public class FlatJSONResponseWriter implements QueryResponseWriter, EmbeddedSolr
                     JSONArray a = new JSONArray();
                     json.put(key, a);
                     for (Object o: ((Collection<?>) value)) {
-                        a.put(o);
+                        a.put(o instanceof Date?sdf.format((Date)o):o);
                     }
                 } else {
-                    json.put(key, value);
+                    json.put(key, value instanceof Date?sdf.format((Date)value):value);
                 }
-            } catch (JSONException e) {
+            } catch (JSONException | IllegalArgumentException | NullPointerException  e) {
                 throw new IOException(e.getMessage());
             }
         }
+        
         writer.write(json.toString());
         writer.write(lb);
     }