apache/beam · error · RuntimeException

Unable to get result coder

Error message

Unable to get result coder

What it means

OrderedEventProcessor.expand() obtains the result coder via handler.getResultCoder(pipeline); a CannotProvideCoderException is rethrown as this RuntimeException. The result coder is required to build the KvCoder for the processor's main output PCollection<KV<EventKeyT, ResultT>>.

Solutions

1. Configure an explicit result coder on the handler (coder supplier for ResultT) at construction time.
2. Register a CoderProvider or add @DefaultCoder to the result class.
3. Override getResultCoder in the handler to return a concrete coder.
4. Verify ResultT's TypeDescriptor resolves to a concrete class.

Example fix

// before
handler -> coder inference fails for MyResult
// after
.setCoderForType(TypeDescriptor.of(MyResult.class), AvroCoder.of(MyResult.class)) // or @DefaultCoder(AvroCoder.class) on MyResult

try {
  handler.getResultCoder(pipeline);
} catch (CannotProvideCoderException e) {
  throw new IllegalStateException("ResultT needs a registered coder; add @DefaultCoder or a coder supplier", e);
}

static <ResultT> boolean resultCoderResolvable(ComposedAccumulatingProcessingHandler<?, ?, ?, ResultT, ?> h, Pipeline p) {
  try { h.getResultCoder(p); return true; } catch (CannotProvideCoderException e) { return false; }
}

try {
  pipeline.apply(processor);
} catch (RuntimeException e) {
  if (e.getCause() instanceof CannotProvideCoderException) {
    throw new IllegalStateException("Set an explicit result coder for ResultT", e);
  }
  throw e;
}

When it happens

Trigger: expand() invoked with a handler whose ResultT type has no inferable coder — custom result class without a CoderProvider, erased generics, or a handler implementation that delegates to coder inference which throws CannotProvideCoderException.

Common situations: Custom result types (e.g. user-defined processing outcome records) without coder registration; changing the ResultT type parameter without updating coder configuration; running on a runner requiring coders earlier than expected.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• ApproximateUnique.PerKey requires its input to use KvCoder
• Could not encode the default value
• Unable to get event coder
• Unable to get key coder
• Unable to get state coder

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/77660a4e16e55158. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/ordered/src/main/java/org/apache/beam/sdk/extensions/ordered/OrderedEventProcessor.java:137

    Coder<EventT> eventCoder;
    try {
      eventCoder = handler.getEventCoder(pipeline, input.getCoder());
    } catch (CannotProvideCoderException e) {
      throw new RuntimeException("Unable to get event coder", e);
    }

    Coder<StateT> stateCoder;
    try {
      stateCoder = handler.getStateCoder(pipeline);
    } catch (CannotProvideCoderException e) {
      throw new RuntimeException("Unable to get state coder", e);
    }

    Coder<ResultT> resultCoder;
    try {
      resultCoder = handler.getResultCoder(pipeline);
    } catch (CannotProvideCoderException e) {
      throw new RuntimeException("Unable to get result coder", e);
    }

    KvCoder<EventKeyT, ResultT> mainOutputCoder = KvCoder.of(keyCoder, resultCoder);
    KvCoder<EventKeyT, OrderedProcessingStatus> processingStatusCoder =
        KvCoder.of(keyCoder, getOrderedProcessingStatusCoder(pipeline));
    KvCoder<EventKeyT, KV<Long, UnprocessedEvent<EventT>>> unprocessedEventsCoder =
        KvCoder.of(
            keyCoder, KvCoder.of(VarLongCoder.of(), new UnprocessedEventCoder<>(eventCoder)));

    if (handler instanceof OrderedProcessingGlobalSequenceHandler) {
      OrderedProcessingGlobalSequenceHandler<EventT, EventKeyT, StateT, ResultT>
          globalSequenceHandler =
              (OrderedProcessingGlobalSequenceHandler<EventT, EventKeyT, StateT, ResultT>) handler;

      return expandGlobalSequenceProcessing(
          input,
          mainOutput,
          statusOutput,

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