If you want to build a Discord bot in Java, you have three serious choices — JDA, Javacord, and Discord4J — and picking one is mostly about the coding style you enjoy, not about what's possible. All three cover the modern Discord API: slash commands, buttons, embeds, the lot. This guide compares them honestly, then points you at the practical build.
| At a glance | |
|---|---|
| You need | A Falix server running the Java application; a bot token |
| Plan | Any — on free it runs while your session timer has time left, premium runs 24/7 |
| Time | Ten minutes to choose |
| New to bots? | Your first Discord bot |
First, the part that's the same for all three
A Discord bot is just a Java program, and the Java application on Falix runs one thing: a runnable fat jar (app.jar by default). Nothing compiles on the server — you build the jar locally or with a Git post-deploy step, bundle every dependency inside it, and upload it. Whichever library you choose, that packaging story is identical, and it's covered in Java on Falix. A pure bot makes only outbound connections to Discord, so it needs no port — SERVER_PORT is irrelevant.
That means your choice of library changes your code, never your hosting. So choose the one you'll enjoy writing.
The three libraries
| Library | Style | Best known for | Pick it when |
|---|---|---|---|
| JDA (Java Discord API) | Plain, imperative Java — event listeners and builder objects | Being the de-facto standard: the biggest community, the most tutorials, the most Stack Overflow answers | You want the safest, best-documented default — especially your first Java bot |
| Javacord | Lightweight, CompletableFuture-based async with a friendly, Optional-heavy API |
A small, approachable surface that's quick to learn | You want something simpler than JDA and don't need every niche feature |
| Discord4J | Reactive, built on Project Reactor (Flux/Mono) |
Fitting cleanly into reactive Java stacks | You already think in reactive streams, or you're integrating with Spring WebFlux / Reactor |
🎯 Good to know: All three work beautifully from Kotlin too — many Java bot authors write JDA bots in Kotlin for the nicer syntax while keeping the same library and the same
app.jarbuild.
JDA — the default
JDA is where most people should start. It models Discord with straightforward objects and event listeners: you register a listener, Discord fires events, you respond. Because it's so widely used, almost any problem you hit has already been answered somewhere, and slash commands, buttons, modals, and embeds all have first-class builders. If you're unsure, this is the answer.
Javacord — the lightweight one
Javacord leans on CompletableFuture for its async calls and uses Optional heavily so you're nudged to handle "not found" cases. The API is smaller and quicker to get your head around than JDA's. It's a genuinely nice fit for a modest bot where you'd rather not learn a large framework — just be aware the community is smaller, so you'll lean more on the official docs than on random tutorials.
Discord4J — the reactive one
Discord4J is the odd one out by design: it's fully reactive, built on Project Reactor, so you compose behaviour with Flux and Mono instead of imperative listeners. If reactive programming already clicks for you — or your bot lives alongside a Reactor/Spring WebFlux codebase — it's elegant. If you've never written reactive Java, the learning curve is real, and JDA will feel far more direct.
How to decide, quickly
- Your first Java bot, or you want maximum help online → JDA.
- You want the smallest, simplest API and a light dependency → Javacord.
- You live in a reactive/Reactor world already → Discord4J.
There's no wrong answer here — all three are mature and actively used. The worst outcome is picking the "clever" option and bouncing off it, so favour the style you already find natural.
Dependencies on the Java application
Whichever you choose, remember there's no Packages page for the Java application (see Java on Falix). You declare the library in your pom.xml or build.gradle, and your fat-jar plugin (Maven Shade or Gradle Shadow) bundles it into app.jar. There's nothing to install on the server — everything the bot needs is already inside the jar you upload.
⚠️ Heads up: A plain jar with no bundled dependencies will start and then crash with
NoClassDefFoundErrorthe moment it touches the Discord library. That's the number-one Java bot mistake here — you must build a fat jar. The fix is in Java on Falix.
The practical path
Reading about libraries only gets you so far. Once you've chosen — and JDA is the recommended starting point — the JDA bot quickstart walks the whole build end to end: a Maven project, a fat jar, the token in a file next to the jar, upload, and start. It's the fastest way from "I picked a library" to "my bot is online".
For depth beyond the Falix-shaped parts, each library owns its own documentation: JDA at jda.wiki, Javacord at javacord.org, and Discord4J at discord4j.com. Those are where you go for the full API.