AVaadin Flow calendar component that does what most others don’t: it treatsCalDAV as a first-class backend, not an afterthought. Drop it into your Vaadin app, point it at iCloud / Nextcloud / Radicale / Baïkal, done.

Positioning

There’s no shortage of calendar UI libraries — FullCalendar, TOAST UI, DHTMLX, Kendo, Bryntum. They render beautifully. They all stop at the backend boundary: “events come from somewhere, you wire it up.”

ChronoGrid takes the other half seriously. It ships:

• A native Vaadin Flow composite — Java API, route-free embedding, Lumo-themable, no JavaScript wrapper work
• A real CalDAV client —PUT/GET/DELETE/REPORT/PROPFIND wire protocol, ETag-based optimistic concurrency, XML-hardened response parsing
• Multi-server, multi-subscription — connect to several CalDAV servers at once, each with its own credentials; subscriptions visible/colored individually
• In-app discovery — three-stepPROPFIND chain (principal → calendar-home-set → list) behind aDiscover calendars button
• Provider quick-connect — one-click presets for common CalDAV providers (Apple iCloud shipped; extension point for Nextcloud / Radicale / Baïkal …)

It isnot trying to be a better FullCalendar at rendering, and it isnot a resource scheduler. The nische isJava + Vaadin + CalDAV + On-Prem + EU-friendly — and that nische is wide open.

Architecture — three modules

The split matters: the core can be usedwithout Vaadin. Acron-driven sync job that reconciles two CalDAV servers? Pullchronogrid-core. A Vaadin dashboard that needs an embedded calendar? Pullchronogrid.

What the demo shows

• Month / Week / Day / N-days view with a custom Lumo-themed nav bar (FullCalendar’s default toolbar is disabled)
• Edit-dialog + drag / drop / resize with conflict notification on ETag mismatch (412 →ConcurrentModificationException)
• Runtime CalDAV settings — switch collection URI and HTTP Basic credentials at runtime, persisted onVaadinSession
• All-connections status board — one row per server, live status pill probed every 15 s
• Per-subscription colour picker with persistence; falls back to the server’s<C:calendar-color> or a deterministic palette
• Per-event target calendar — when multiple subscriptions are active, the New-event dialog grows aServer +Calendar filter so you control where thePUT lands
• Zebra calendar grid — subtle alternating tint, CSS-only, scoped to FullCalendar’s class names

Ecosystem play

ChronoGrid sits at the centre of two other small projects on this site:

• caldav-testbench — the in-memory CalDAV server the demo uses for local development. Same wire protocol as Nextcloud / Radicale, no auth, no persistence. Boot in one terminal, develop against it in another.
• nano-vaadin-jetty — embedded Jetty launcher the demo wraps to ship as a single executable JAR.

The “real provider” the blog series connects to isApple iCloud — plain CalDAV with HTTP Basic + app-specific password, no special-casing needed.

Why a separate component

This started as an internal Vaadin app that needed a CalDAV-backed calendar. The realisation: every Vaadin app that ever needs calendar functionality hits this same gap. FullCalendar gives you rendering. Everything between rendering and a real iCloud/Nextcloud account — wire protocol, discovery, conflict handling, multi-source merging, connection lifecycle — is work each project re-invents. ChronoGrid is that work, extracted and packaged.

Status

🟡WIP — actively developed (created June 2026). API surface is stabilising; expect pre-1.0 breaking changes in thehandler,report andxml packages ofchronogrid-core. The public API surface is:

• com.svenruppert.chronogrid.client — the wire client
• com.svenruppert.chronogrid.service — the orchestration façade
• com.svenruppert.chronogrid.ui.ChronoGrid — the Vaadin composite

License isEUPL-1.2 — copyleft-style, EU-approved equivalent to LGPL. A blog series walking through the architecture is in the works.

Further reading

• Roadmap — what’s coming next, and what’s deliberately out of scope. Derived from the competitive analysis.
• Comparison matrix — head-to-head against FullCalendar Flow, Scheduler, TOAST UI, DHTMLX, Kendo and Bryntum. Rendering, event interaction, backend integration, Vaadin support — all four dimensions.