Refactor: Add cleanup hook

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/database/DatabaseHandler.java

@@ -36,7 +36,6 @@ public class DatabaseHandler {
 
     public DatabaseHandler(){
         try {
-//           Cleanup hook Runtime.getRuntime().addShutdownHook(new Thread(() -> {}));
             String jdbcurl = H2GISDBFactory.createDataSource(DB_NAME,
                     true, ";AUTO_SERVER=TRUE").getConnection().getMetaData().getURL();
             HikariDataSource ds = new HikariDataSource();
@@ -50,6 +49,8 @@ public class DatabaseHandler {
 
             dataSource = new DataSourceWrapper(ds);
 
+            //Cleanup hook
+            Runtime.getRuntime().addShutdownHook(new Thread(ds::close));
         } catch (Exception e) {
             logger.fatal("FATAL ERROR: Creation of embedded database failed!");
             logger.fatal(e.getMessage());