Node.js → Java feature map

You know Node.js Moleculer; this page maps what you already do to its Java equivalent — including the honest "there is no equivalent" entries, so you stop searching for features that were intentionally left out. Each row links to the page with the details.

The wire protocol, addressing (service.action), transporters, serializers, cachers and balancing strategies are the same on both sides — that is what lets a Java and a Node.js node share one cluster. The differences below are all on the programming-model side, inside a single node.

Defining a service

Node.js	Java	Notes
module.exports = { name: "math", actions: {...} }	@Name("math") public class MathService extends Service { ... }	A class, not a schema object. Services
actions: { add(ctx) { ... } }	public Action add = ctx -> { ... };	An action is a public instance field (a lambda), never static. Services
methods: { helper() {} }	a plain Java method on the class	No special methods block.
settings: { ... } / this.settings	plain fields on the class; broker-wide options via ServiceBrokerConfig	No settings object. Broker
metadata: { ... }	annotations on the class/action (read as a Tree in middleware)	Middlewares
mixins (e.g. the gateway is a mixin)	✗ none — use normal inheritance or shared helper classes	Composition is plain Java.
created() / merged()	✗ none — use the constructor	Lifecycle
started() / stopped()	started(ServiceBroker broker) / stopped()	Call super.started(broker). Lifecycle
action hooks (before/after/error)	a Middleware that wraps the Action	One mechanism for all three. Middlewares
action visibility: "published"/"public"/"protected"/"private"	field visibility: public = published to the cluster; private → protected (local-only)	Services
declarative params validation (fastest-validator)	✗ none — validate ctx.params manually or in a Middleware	Validating parameters

Data & async

Node.js	Java	Notes
a JavaScript object (ctx.params, payloads)	an io.datatree.Tree	The one data type. Tree quick reference
ctx.params.a	ctx.params.get("a", default)	Typed getter with a default. Tree
ctx.meta	ctx.params.getMeta() (also ctx.meta)	Metadata
Promise / .then() / .catch()	io.datatree.Promise / .then() / .catchError()	ES6-style, not java.util.concurrent. Concepts
async / await	.then(...) chaining, or .waitFor(ms) to block	waitFor is the blocking form of await.
share a variable across .then() blocks	write into a final container (Tree, AtomicReference, 1-element array)	A correctness rule. Concepts
Promise.all([...])	Promise.all(...)	Same idea.
streams	PacketStream (broker.createStream())	Streaming

Calling actions & events

Node.js	Java	Notes
broker.call("svc.action", { a: 1 })	broker.call("svc.action", params) or broker.call("svc.action", "a", 1)	Object or key–value varargs. Calling actions
call options { timeout, retries, fallbackResponse }	CallOptions.timeout(long).retryCount(int)	timeout+retryCount only — no fallbackResponse. Call options
mcall([...])	Promise.all(call1, call2, ...)	No mcall; combine promises.
ctx.emit / ctx.broadcast	ctx.emit / ctx.broadcast; broker.emit/broadcast/broadcastLocal	Events
$node.list/services/actions/events/health	same names	Internal services
$node.metrics / $node.options (actions)	✗ none	No $node.metrics action — but metrics do exist (Micrometer); see Tooling & runtime below.

Fault tolerance

Node.js	Java	Notes
Circuit Breaker	✓	Fault tolerance
Retry	✓ CallOptions.retryCount(int)
Timeout	✓ CallOptions.timeout(long)	milliseconds
Bulkhead	✗ none — limit concurrency yourself	Fault tolerance
Fallback (fallbackResponse)	✗ none — handle it with .catchError(...) on the caller

Tooling & runtime

Node.js	Java	Notes
broker.logger	SLF4J (a facade + a binding you pick)	Logging
moleculer-runner (config-driven loader, --hot)	the Java "Runner" is a different thing — a Spring app start/stop/install helper	⚠️ Not the same. Runner
broker.loadServices("./services")	✗ none — register with broker.createService(...)
--hot hot reload	✗ none — restart the broker
cachers, transporters, serializers, strategies	the same set, Node-compatible	Caching · Transporters · Serializers
Metrics (metrics: { enabled })	✓ Micrometer-based — off until metricsEnabled(true)	Metrics & tracing
built-in tracing (tracing, Jaeger/Zipkin)	✗ none — propagate via meta, or use an external APM	Metrics & tracing
moleculer-db / moleculer-io (ecosystem)	✗ no general port — moleculer-java-mongo (DB), Web WebSocket (io)	MongoDB · WebSocket

---

New here? The shortest path from this map to a running node is the Minimal Java service for Node.js developers — one class, one action, NATS, called from your existing Node.js system.