The current UI from the user’s point of view # On the first call, the user lands in the overview. The site is built on a Vaadin grid, whose header contains a search bar, paging controls, and a small settings button with a gear icon. The most essential flow begins with the table displaying immediately understandable columns: the shortcode as a clearly typographically separated monospace value with copy action, the original URL as a clickable link, a creation time in local format, and an expiration badge that visually communicates semantic states such as “Expired”, “Today” or “in n days” via theme colours. The whole thing is designed for quick viewing and efficient one-handed operation: a click on a data record opens the detailed dialogue if required; a right-click or the context menu offers direct quick actions; and the gear button can be used to show or hide visible columns live.
Server-Side Extension: PreferencesHandler and REST Interfaces # The server-side extension for dynamic column visibility follows the same design logic as the UI: simplicity, clear accountability, and a precise data flow. While the OverviewView and the ColumnVisibilityDialog form the interface for the interaction, several specialized REST handlers handle the processing and persistence of the user settings. Their job is to process incoming JSON requests, validate them, translate them into domain operations, and return or store the current state.
From observer to designer: User control at a glance # With the fourth day of the Advent calendar, the perspective on the application changes fundamentally. While in the previous expansion stages users reacted primarily to prepared structures, an element of active design is now being added. The “Overview” has so far been a central mirror of the system state: It showed all saved short links, allowed them to be filtered and provided an in-depth insight into individual objects with the detailed dialog. But the structure and visibility of the columns were immutable up to this point. The user always saw the selection that the developer had defined as meaningful. With the introduction of dynamic column visibility, this state is removed.
Client contract from a UI perspective # In this project, the user interface not only serves as a graphical layer on top of the backend, but is also part of the overall contract between the user, the client, and the server. This part focuses on the data flow from the UI’s perspective: how inputs are translated into structured requests, how the client forwards them, and what feedback the user interface processes.
Classification and objectives from a UI perspective # Today’s Advent Calendar Day focuses specifically on the interaction level prepared in the previous parts. While the basic structure of the user interface and the layout were defined at the beginning, and the interactive table view with sorting, filtering and dynamic actions was subsequently established, it is now a matter of making the transition from overview to detailed observation consistent. The user should no longer only see a tabular collection of data points, but should receive a view tailored to the respective object that enables contextual actions.
Today, we will finally integrate the StoreIndicator into the UI.
Vaadin integration: live status of the store Implementation of the StoreIndicator Refactoring inside – The MappingCreator as a central logic. EclipseStore – The Persistent Foundation Additional improvements in the core Before & After – Impact on the developer experience The source code for this version can be found on GitHub athttps://github.com/svenruppert/url-shortener/tree/feature/advent-2025-day-02
**Visible change: When the UI shows the memory state
With the end of the last day of the Advent calendar, our URL shortener was fully functional: the admin interface could filter, sort, and display data page by page – performant, cleanly typed, and fully implemented in Core Java. But behind this surface lurked an invisible problem: All data existed only in memory. As soon as the server was restarted, the entire database was lost.
December 2025 is all about a project that has grown steadily in recent months: the Java-based URL Shortener, an open-source project implemented entirely with Core Java, Jetty, and Vaadin Flow. The Advent calendar accompanies users every day with a new feature, a technical deep dive, or an architectural improvement – from the basic data structure and REST handlers to UI components and security aspects.
