diff -r cf85ef18f231 -r e722861558bb src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java
--- a/src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java	Mon May 11 19:09:06 2020 +0200
+++ b/src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java	Tue May 12 22:03:00 2020 +0200
@@ -60,12 +60,6 @@
      */
     private LightPITModule.ELProxy moduleInfo = null;
 
-
-    @FunctionalInterface
-    private interface HandlerMethod {
-        ResponseType apply(HttpServletRequest request, HttpServletResponse response, DataAccessObjects dao) throws IOException, SQLException;
-    }
-
     /**
      * Invocation mapping gathered from the {@link RequestMapping} annotations.
      * <p>
@@ -75,7 +69,7 @@
      * The reason for this is the different handling of empty paths in
      * {@link HttpServletRequest#getPathInfo()}.
      */
-    private final Map<HttpMethod, Map<String, HandlerMethod>> mappings = new HashMap<>();
+    private final Map<HttpMethod, Map<String, Method>> mappings = new HashMap<>();
 
     /**
      * Gives implementing modules access to the {@link ModuleManager}.
@@ -95,12 +89,10 @@
      */
     private DataAccessObjects createDataAccessObjects(Connection connection) throws SQLException {
         final var df = (DatabaseFacade) getServletContext().getAttribute(DatabaseFacade.SC_ATTR_NAME);
-        switch (df.getSQLDialect()) {
-            case Postgres:
-                return new PGDataAccessObjects(connection);
-            default:
-                throw new AssertionError("Non-exhaustive switch - this is a bug.");
+        if (df.getSQLDialect() == DatabaseFacade.Dialect.Postgres) {
+            return new PGDataAccessObjects(connection);
         }
+        throw new AssertionError("Non-exhaustive if-else - this is a bug.");
     }
 
     private ResponseType invokeMapping(Method method, HttpServletRequest req, HttpServletResponse resp, DataAccessObjects dao) throws IOException {
@@ -160,9 +152,9 @@
 
                         final String requestPath = "/" + mapping.get().requestPath();
 
-                        if (mappings.computeIfAbsent(mapping.get().method(), k -> new HashMap<>()).
-                                putIfAbsent(requestPath,
-                                        (req, resp, dao) -> invokeMapping(method, req, resp, dao)) != null) {
+                        if (mappings
+                                .computeIfAbsent(mapping.get().method(), k -> new HashMap<>())
+                                .putIfAbsent(requestPath, method) != null) {
                             LOG.warn("{} {} has multiple mappings",
                                     mapping.get().method(),
                                     mapping.get().requestPath()
@@ -232,10 +224,10 @@
         req.getRequestDispatcher(HTML_FULL_DISPATCHER).forward(req, resp);
     }
 
-    private Optional<HandlerMethod> findMapping(HttpMethod method, HttpServletRequest req) {
-        return Optional.ofNullable(mappings.get(method)).map(
-                (rm) -> rm.get(Optional.ofNullable(req.getPathInfo()).orElse("/"))
-        );
+    private Optional<Method> findMapping(HttpMethod method, HttpServletRequest req) {
+        return Optional.ofNullable(mappings.get(method))
+                .map(rm -> rm.get(Optional.ofNullable(req.getPathInfo()).orElse("/"))
+                );
     }
 
     private void forwardAsSpecified(ResponseType type, HttpServletRequest req, HttpServletResponse resp)
@@ -277,15 +269,24 @@
         final var db = (DatabaseFacade) req.getServletContext().getAttribute(DatabaseFacade.SC_ATTR_NAME);
         try (final var connection = db.getDataSource().getConnection()) {
             final var dao = createDataAccessObjects(connection);
-            // call the handler, if available, or send an HTTP 404 error
-            final var mapping = findMapping(method, req);
-            if (mapping.isPresent()) {
-                forwardAsSpecified(mapping.get().apply(req, resp, dao), req, resp);
-            } else {
-                resp.sendError(HttpServletResponse.SC_NOT_FOUND);
+            try {
+                connection.setAutoCommit(false);
+                // call the handler, if available, or send an HTTP 404 error
+                final var mapping = findMapping(method, req);
+                if (mapping.isPresent()) {
+                    forwardAsSpecified(invokeMapping(mapping.get(), req, resp, dao), req, resp);
+                } else {
+                    resp.sendError(HttpServletResponse.SC_NOT_FOUND);
+                }
+                connection.commit();
+            } catch (SQLException ex) {
+                LOG.warn("Database transaction failed (Code {}): {}", ex.getErrorCode(), ex.getMessage());
+                LOG.debug("Details: ", ex);
+                resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "Unhandled Transaction Error - Code:" + ex.getErrorCode());
+                connection.rollback();
             }
         } catch (SQLException ex) {
-            LOG.error("Database exception (Code {}): {}", ex.getErrorCode(), ex.getMessage());
+            LOG.error("Severe Database Exception (Code {}): {}", ex.getErrorCode(), ex.getMessage());
             LOG.debug("Details: ", ex);
             resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "Database Error - Code:" + ex.getErrorCode());
         }