diff -r bd1a76c91d5b -r b213fef2539e src/java/de/uapcore/lightpit/entities/ModuleDao.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java/de/uapcore/lightpit/entities/ModuleDao.java	Sun Apr 01 18:16:47 2018 +0200
@@ -0,0 +1,147 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ * 
+ * Copyright 2017 Mike Becker. All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ */
+package de.uapcore.lightpit.entities;
+
+import de.uapcore.lightpit.LightPITModule;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.AbstractMap;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+public abstract class ModuleDao {
+    
+    /**
+     * Must return a prepared statement for a single object query with the specified properties.
+     * 
+     * <ul>
+     * <li>Parameter 1: classname</li>
+     * <li>Result field 1: visible</li>
+     * </ul>
+     * 
+     * @param conn the connection to use
+     * @return the prepared statement
+     * @throws SQLException 
+     */
+    protected PreparedStatement moduleCheckStatement(Connection conn) throws SQLException {
+        return conn.prepareStatement("SELECT visible FROM lpitcore_module WHERE classname = ?");
+    }
+    
+    /**
+     * Must return a prepared statement for insertion with the specified properties.
+     * 
+     * <ul>
+     * <li>Parameter 1: classname</li>
+     * <li>Parameter 2: visible</li>
+     * </ul>
+     * 
+     * @param conn the connection to use
+     * @return the prepared statement
+     * @throws SQLException 
+     */
+    protected PreparedStatement moduleInsertStatement(Connection conn) throws SQLException {
+        return conn.prepareStatement("INSERT INTO lpitcore_module (classname, visible) VALUES (?, ?)");
+    }
+    
+    /**
+     * Synchronizes a set of registered module classes with the database and gives a list of visible modules in return.
+     * 
+     * Inserts module classes which are not known to the database and sets them to be visible by default.
+     * Module classes known to the database, which are not in the given set, are ignored.
+     * 
+     * @param conn the connection to use
+     * @param moduleSet the module set to synchronize
+     * @return a list of elements from the given set, which should be visible in the menu
+     * @throws SQLException
+     */
+    public final List<Map.Entry<String, LightPITModule>>
+            syncRegisteredModuleClasses(Connection conn, Set<Map.Entry<String, LightPITModule>> moduleSet) throws SQLException {
+                
+        PreparedStatement
+                check = moduleCheckStatement(conn),
+                insert = moduleInsertStatement(conn);
+        insert.setBoolean(2, true);
+        // update/delete not required, we do this in the module management UI
+
+        final List<Map.Entry<String, LightPITModule>> visibleModules = new ArrayList<>();
+
+        for (Map.Entry<String, LightPITModule> mod : moduleSet) {
+            if (mod.getValue().systemModule()) continue;
+
+            check.setString(1, mod.getKey());
+            try (ResultSet r = check.executeQuery()) {
+                final boolean visible;
+                if (r.next()) {
+                    visible = r.getBoolean(1);
+                } else {
+                    insert.setString(1, mod.getKey());
+                    insert.executeUpdate();
+                    visible = !mod.getValue().menuKey().isEmpty();
+                }
+                if (visible) {
+                    visibleModules.add(new AbstractMap.SimpleEntry<>(
+                            mod.getKey(),
+                            mod.getValue()
+                    ));
+                }
+            }
+        }
+        return visibleModules;
+    }
+
+    /**
+     * Returns a list of all modules known by the database.
+     * 
+     * Keep in mind, that system modules are never known to the database.
+     * 
+     * @param conn the connection to use
+     * @return a list of all modules known by the database
+     * @throws SQLException 
+     */
+    public List<Module> listAll(Connection conn) throws SQLException {
+        List<Module> list = new ArrayList<>();
+        try (
+                Statement stmt = conn.createStatement();
+                ResultSet result = stmt.executeQuery("SELECT * FROM lpitcore_module")) {
+            while (result.next()) {
+                final Module mod = new Module();
+                mod.setModID(result.getInt("modid"));
+                mod.setClassname(result.getString("classname"));
+                mod.setVisible(result.getBoolean("visible"));
+                list.add(mod);
+            }
+        }
+        return list;
+    }
+}