Vaadin

In the previous part, we looked at the implementation on the server side. This part is now about the illustration on the user page. The source code for the initial state can be found on GitHub under https://github.com/svenruppert/url-shortener/tree/feature/advent-2025-day-00 .

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.

1. Introduction and motivation # The observer pattern is one of the basic design patterns of software development and is traditionally used to decouple state changes and process them. Its origins lie in the development of graphical user interfaces, where a shift in the data model required synchronising several views immediately, without a direct link between these views. This pattern quickly established itself as the standard solution to promote loosely coupled architectures.

From my experience, Vaadin has always stood out from other Java frameworks. Of course, it enables the creation of modern web UIs, but the real difference lies in its component architecture. This is not conceived as a short-term aid, but is consistently designed for maintainability and flexibility. It creates the possibility of running applications stably for many years while still being able to extend them step by step.

1. Introduction and objectives # The first two parts of this series established the theoretical and practical foundations of a URL shortener in pure Java. We discussed the semantic classification of short URLs, the architecture of a robust mapping system, and the implementation of a REST-based service based on the JDK HTTP server. These efforts resulted in a functional, modularly extensible backend that creates, manages, and efficiently resolves short links. However, a crucial component was missing-a visual interface for direct user interaction with the system. This interface is essential for tasks such as manual link creation, viewing existing mappings, and analysing individual redirects.

1. Introduction # Why REST integration in Vaadin applications should not be an afterthought # In modern web applications, communication with external services is no longer a special function, but an integral part of a service-oriented architecture. Even if Vaadin Flow, as a UI framework, relies on server-side Java logic to achieve a high degree of coherence between view and data models, the need to communicate with systems outside the application quickly arises. These can be simple public APIs—for example, for displaying weather data or currency conversions—as well as internal company services, such as license verification, user management, or connecting to a central ERP system.

A deep look into Java’s HashMap traps – visually demonstrated with Vaadin Flow. The silent danger in the standard library # The use of HashMap and HashSet is a common practice in everyday Java development. These data structures offer excellent performance for lookup and insert operations, as long as their fundamental assumptions are met. One of them is hashCode() of a key remains stable. But what if that’s not the case?

Vaadin Flow is a robust framework for building modern web applications in Java, where all UI logic is implemented on the server side. In this blog post, we’ll make a simple file management application step by step that allows users to upload files, save them to the server, and download them again when needed. This is a great way to demonstrate how to build protection against CWE-22, CWE-377, and CWE-778 step by step.

The world of cybersecurity is full of threats, many of which are surprisingly subtle and challenging to detect. One such threat is the problem of so-called homoglyphs. CWE-1007, also known as “Insufficient Visual Distinction of Homoglyphs Presented to User”, is a vulnerability often used by attackers to deceive and compromise your systems or data. In this blog article, you will get a deep insight into CWE-1007, understand its mechanisms, and how to protect yourself from such attacks. We will discuss examples, technical challenges, and best practices that can help you as a developer understand and mitigate this threat.

Tapestry, Wicket, and Vaadin # A component-oriented Java web application framework is a development framework that enables the construction of web applications in a modular way, using reusable, encapsulated components that manage their state, behaviour, and presentation. This approach allows developers to build complex user interfaces by assembling pre-built or custom components, like building blocks, each handling specific functionalities within the application.

In this part of the series about Vaadin Flow, I will show how I can create the basic framework for the graphic design of a work application. The focus here is on the design of the work area and the organisation of the individual logical application groups. In other words, we create the application layout that can be used for an industrial project.

We will now create a new Vaadin Flow application step by step and create a basic framework for our own projects with this component-based open-source web framework. So, right from the start, the question arises: How can you start with as little effort as possible without avoiding the usual expenses that sometimes come with creating projects?