protected void doCommon(HttpServletRequest request, HttpServletResponse response)
    {
        final HttpSession session = request.getSession();
        final WebManager webManager = new WebManager();
        webManager.init(request, response, session, session.getServletContext());

        final PluginManager pluginManager = webManager.getXMPPServer().getPluginManager();
        final UpdateManager updateManager = XMPPServer.getInstance().getUpdateManager();

        request.setAttribute("webManager", webManager);
        request.setAttribute("pluginManager", pluginManager);
        request.setAttribute("updateManager", updateManager);

        request.setAttribute("plugins", pluginManager.getMetadataExtractedPlugins());
        request.setAttribute("uploadEnabled", PLUGINS_UPLOAD_ENABLED.getValue());
        request.setAttribute("serverVersion", XMPPServer.getInstance().getServerInfo().getVersion());
    }
Defines the expected content-type of uploaded plugin files.
xmppserver/src/main/java/org/jivesoftware/admin/servlet/PluginServlet.java