apache/beam · error · RuntimeException

Unable to get state coder

Error message

Unable to get state coder

What it means

OrderedEventProcessor.expand() requests the state type StateT coder via handler.getStateCoder(pipeline). Unlike key/event coders it is not inferred from the input PCollection, so if the handler cannot supply one (CannotProvideCoderException), this RuntimeException is thrown. State must be serializable because Beam persists per-key state and buffers.

Solutions

1. Provide an explicit state coder when constructing the handler/builder (e.g. usingSerializableCoder/AvroCoder supplier).
2. Annotate the state class with @DefaultCoder or register a CoderProvider in the pipeline's CoderRegistry.
3. Override getStateCoder in a handler subclass to return a concrete Coder<StateT>.
4. Check that the StateT generic parameter is concrete at the call site.

Example fix

// before
OrderedEventProcessor<KeyT, EventT, StateT, ...> p = OrderedEventProcessor.builder(handler)...build();
// after (handler supplies coder)
OrderedEventProcessor.Builder<...> b = OrderedEventProcessor.builder(handlerWithStateCoder(SerializableCoder.of(MyState.class)));

Objects.requireNonNull(stateCoderSupplier, "state coder supplier must be configured on the handler before build()");

static <StateT> boolean stateCoderConfigured(ComposedAccumulatingProcessingHandler<?, ?, StateT, ?, ?> h) {
  try { return h.getStateCoder(pipeline) != null; } catch (CannotProvideCoderException e) { return false; }
}

try {
  handler.getStateCoder(pipeline);
} catch (CannotProvideCoderException e) {
  throw new IllegalStateException("Provide an explicit Coder<StateT> in the handler configuration", e);
}

When it happens

Trigger: Building OrderedEventProcessor with a state class that has no registered coder provider and no explicit coder configured on the handler; calling expand() where getStateCoder relies on type inference that fails for the custom StateT.

Common situations: State classes without @DefaultCoder or CoderProvider registration; using nested generic state types whose TypeDescriptor cannot be materialized; forgetting to pass a coder supplier when constructing the handler.

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
• set or map state type
• Unable to get event coder
• Unable to get key coder

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/9eea0ed822371c22. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/ordered/src/main/java/org/apache/beam/sdk/extensions/ordered/OrderedEventProcessor.java:130

    Coder<EventKeyT> keyCoder;
    try {
      keyCoder = handler.getKeyCoder(pipeline, input.getCoder());
    } catch (CannotProvideCoderException e) {
      throw new RuntimeException("Unable to get key coder", e);
    }

    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>

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