apache/beam · error · UnsupportedOperationException

MultiOutputReceiver unsupported in

Error message

MultiOutputReceiver unsupported in %s

What it means

taggedOutputReceiver() throws UnsupportedOperationException because the invoker implementation has no MultiOutputReceiver bound. Multi-output (tagged) DoFns need this to write to named output tags. The error context names the unsupported invoker.

Solutions

1. Provide a multiOutputReceiver factory (e.g. DoFnInvoker.MultiOutputProvider) when building the invoker
2. Use the runner's ProcessContext, which implements tagged outputs, rather than the base invoker
3. In tests use DoFnTester.takeOutputTag or wire tagged receivers
4. If only main output is needed, switch the code path to outputReceiver

Example fix

// before
DoFnInvoker invoker = DoFnInvokers.newInvoker(doFn);
invoker.taggedOutputReceiver(doFn).get(tag).output(v); // throws
// after
DoFnInvoker invoker = DoFnInvokers.newInvoker(doFn,
    DoFnInvoker.MultiOutputProvider.boundToMap(tagMap));

boolean multi = !doFnTagMap.isEmpty(); // only need tagged receiver for multi-output DoFns

null

try { invoker.taggedOutputReceiver(doFn).get(tag).output(v); } catch (UnsupportedOperationException e) { /* route to fallback receiver */ }

When it happens

Trigger: DoFn.ProcessElement code calling c.output(tag, value) when the invoker's taggedOutputReceiver has no factory; direct invocation of taggedOutputReceiver(DoFn) on a DelegatingDoFnInvoker.

Common situations: Running a multi-output DoFn through a minimal invoker or test harness that only supports single output; custom batch/windowing utilities invoking the DoFn directly.

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/1131436bbe97a353. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/reflect/DoFnInvoker.java:408

      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(
          String.format("BoundedWindow unsupported in %s", getErrorContext()));
    }

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

    @Override
    public PipelineOptions pipelineOptions() {
      throw new UnsupportedOperationException(

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