apache/beam · error · UnsupportedOperationException

OutputReceiver unsupported in

Error message

OutputReceiver unsupported in %s

What it means

outputReceiver() is unsupported in this invoker implementation: the base class throws UnsupportedOperationException because no OutputReceiver factory was supplied. The invoker cannot route the DoFn's main outputs without a receiver. The error context in the message identifies which invoker was used.

Solutions

1. Supply an outputReceiverFactory when creating the invoker
2. Use the runner's normal invocation path (DoFnProcessContext) instead of invoking via the raw invoker
3. In tests, use DoFnTester which wires receivers, or register a test OutputReceiver
4. Capture main-bundle output via a ProcessContext implementation rather than the base invoker

Example fix

// before
DoFnInvoker invoker = DoFnInvokers.newInvoker(doFn);
invoker.invokeProcessElement(context); // context.output() throws
// after
DoFnInvoker invoker = DoFnInvokers.newInvoker(doFn,
    DoFnInvoker.OutputProvider.boundTo((OutputReceiver<Object>) receiver));

boolean hasOutput = invoker instanceof /* concrete invoker with output support */ ;

null

try { invoker.outputReceiver(doFn).output(v); } catch (UnsupportedOperationException e) { throw new IllegalStateException("Invoker lacks output receiver", e); }

When it happens

Trigger: Invoking outputReceiver(DoFn) on a DelegatingDoFnInvoker or generated invoker built without an outputReceiverFactory; DoFn code calling c.output(...) when the invoker lacks a bound receiver.

Common situations: Custom invocation code (e.g. testing frameworks, state/timer utilities) that invokes the DoFn directly without wiring output receivers; using DoFnInvokers.newInvoker with a restricted factory set.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• BoundedWindow unsupported in
• Cannot access fire timestamp outside of @OnTimer method.
• Cannot access OnTimerContext outside of @OnTimer methods.
• Cannot access OnWindowExpirationContext outside of…
• Cannot access time domain outside of @ProcessTimer method.

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/fa68df5cf717c751. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/reflect/DoFnInvoker.java:396

      throw new UnsupportedOperationException(
          String.format("TimerId unsupported in %s", getErrorContext()));
    }

    @Override
    public TimeDomain timeDomain(DoFn<InputT, OutputT> doFn) {
      throw new UnsupportedOperationException(
          String.format("TimeDomain unsupported in %s", getErrorContext()));
    }

    @Override
    public OutputReceiver<OutputT> outputReceiver(DoFn<InputT, OutputT> doFn) {
      throw new UnsupportedOperationException(
          String.format("OutputReceiver unsupported in %s", getErrorContext()));
    }

    @Override
    public OutputReceiver<Row> outputRowReceiver(DoFn<InputT, OutputT> doFn) {
      throw new UnsupportedOperationException(
          String.format("Row OutputReceiver unsupported in %s", getErrorContext()));
    }

    @Override
    public MultiOutputReceiver taggedOutputReceiver(DoFn<InputT, OutputT> doFn) {
      throw new UnsupportedOperationException(
          String.format("MultiOutputReceiver unsupported in %s", getErrorContext()));
    }

    @Override
    public Object restriction() {
      throw new UnsupportedOperationException(
          String.format("Restriction unsupported in %s", getErrorContext()));
    }

    @Override
    public BoundedWindow window() {
      throw new UnsupportedOperationException(

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