Style: Add error log for checks

CityDoctorParent/CityDoctorValidation/src/main/java/de/hft/stuttgart/citydoctor2/check/Checker.java

@@ -672,7 +672,9 @@ public class Checker {
                 if (!missedFeatures.isEmpty()){
                     //TODO: Localize String
                     logger.error("Checker still unable to load some CityObjects from database!");
-                    logger.debug(missedFeatures.toString());
+                    if (logger.isDebugEnabled()){
+                        logger.debug(missedFeatures.toString());
+                    }
                 }
             }
             long endTime = System.nanoTime();
@@ -693,7 +695,8 @@ public class Checker {
                 }
 
             } catch (InterruptedException e) {
-                throw new RuntimeException(e);
+                Thread.currentThread().interrupt();
+                logger.error("Main Thread got interrupted during ThreadPool shutdown");
             }
         }
     }
@@ -726,11 +729,13 @@ public class Checker {
                 return null;
             });
         }
+        logger.trace("Queueing up finished, invoking all tasks");
         return exec.invokeAll(tasks);
     }
 
     private List<GmlId> getMissedFeatures(List<Future<GmlId>> futures) throws InterruptedException{
         List<GmlId> missedList = new ArrayList<>();
+        Set<ExecutionException> errors = new HashSet<>();
         for (Future<GmlId> future : futures) {
             try{
                 GmlId gmlId = future.get();
@@ -740,8 +745,13 @@ public class Checker {
             } catch (ExecutionException e){
                 logger.debug("A Task failed due to an unexpected exception", e);
                 logger.debug(e.getCause());
+                errors.add(e);
             }
         }
+        if (!errors.isEmpty()) {
+            logger.error("Encountered check failures due to the following errors:");
+            logger.error(errors.toString());
+        }
         return missedList;
     }