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Troubleshooting

A short checklist of common issues and how to fix them when building and running Fluxtion DataFlows.

Nothing happens when I send events

  • Verify you actually subscribed to the right type or key:
  • subscribe(String.class) for raw String events
  • subscribe(MyEvent::field) if you want to project a field from a POJO
  • Ensure you call build() (functional DSL) or finish constructing the SEP before invoking onEvent.
  • If using sinks, confirm you added a sink or a console call at the end of the chain: .console("msg:{}") or .sink("id").

Time windows not updating

  • Windowing operators depend on time; register a clock source. At startup publish a clock event using ClockStrategy: 
    import static com.telamin.fluxtion.runtime.time.ClockStrategy.registerClockEvent;

dataFlow.onEvent(registerClockEvent(() -> System.currentTimeMillis()));
  • In tests, use a controllable clock. If you extend the provided test utilities, call setTime(...), advanceTime(...), or tick() to drive time.

Determinism and order look wrong

  • Fluxtion executes nodes in topological order with at‑most‑once invocation per node per event. If results seem stale:
  • Check each node declares its dependency via the builder chain (e.g., ensure the node that should trigger another is actually upstream).
  • Avoid side effects that bypass the graph; instead pass values through the DataFlow so dependencies are tracked.

Logging and debugging

  • Quick visibility: add .console("msg:{}") at the end of a chain to print values.
  • For structured auditing, enable the event log auditor (see reference) and inspect the last audit record via dataFlow.getLastAuditLogRecord().
  • Tests include logcaptor and system-rules to capture output if you need assertions on logs.

IDE or tests fail with IllegalAccessError

  • The build config opens jdk.internal.misc for some dependencies via Surefire:
  • Maven Surefire already includes: --add-opens java.base/jdk.internal.misc=ALL-UNNAMED.
  • If running in your IDE, mirror this JVM option in your run configuration if you encounter IllegalAccess problems.

Java version

  • Fluxtion targets Java 21. Ensure your project uses a Java 21 toolchain and your IDE is set to 21 for compiling and running examples.

Kafka or external I/O integration

  • Fluxtion is infrastructure‑agnostic. For Kafka, consume records, publish to the DataFlow via onEvent, then produce results. Start with at‑least‑once: commit offsets after successful processing. See the Integrations guide.

Still stuck?

  • Check the Examples page and Reference guide for a code snippet matching your use case.
  • Open an issue with a minimal reproducer on GitHub if the behavior still surprises you.