apache/beam · error · UnsupportedOperationException

Not supported.

Error message

Not supported.

What it means

SingleValueCollector.asContext always throws UnsupportedOperationException; the collector wraps a single element directly and intentionally has no Context view, because the underlying functor never needs one.

Solutions

1. Do not call asContext() on single-value collectors; use the collector's direct methods (getCounter, getHistogram, collect)
2. Branch on collector type before calling asContext()
3. Restructure code so context-based access happens only in element collectors

Example fix

// before
Context ctx = collector.asContext();
// after
if (collector instanceof ElementCollector) { Context ctx = ((ElementCollector) collector).asContext(); }

if (collector instanceof SingleValueCollector) { /* don't call asContext() */ }

Optional<Context> tryAsContext(Collector<?> c) { return (c instanceof SingleValueCollector) ? Optional.empty() : Optional.of(((ElementCollector<?>) c).asContext()); }

try { ctx = collector.asContext(); } catch (UnsupportedOperationException e) { /* use direct collector methods instead */ }

When it happens

Trigger: Calling collector.asContext() on a SingleValueCollector, e.g. generic code that treats every collector uniformly and requests a context for accumulator/timer operations.

Common situations: Framework-style user code iterating collectors of different kinds; someone attempting to use context-based (windowed/element-context) APIs in a single-value collection.

Related errors

• Accumulators not supported in this context
• Cannot access OnTimerContext outside of @OnTimer methods.
• Cannot access OnWindowExpirationContext outside of…
• Cannot determine context class
• Cannot translate Euphoria 'Join' operator to Beam…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/8a9a5996033a9767. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/euphoria/src/main/java/org/apache/beam/sdk/extensions/euphoria/core/translate/collector/SingleValueCollector.java:65

  public SingleValueCollector(AccumulatorProvider accumulators, @Nullable String operatorName) {
    this.accumulators = accumulators;
    this.operatorName = operatorName;
  }

  public T get() {
    return elem;
  }

  @Override
  public void collect(T elem) {
    this.elem = elem;
  }

  @Override
  public Context asContext() {
    // this is not needed, the underlying functor does not have access to this
    throw new UnsupportedOperationException("Not supported.");
  }

  @Override
  public Counter getCounter(String name) {
    return accumulators.getCounter(requireNonNull(operatorName, UNSUPPORTED), name);
  }

  @Override
  public Histogram getHistogram(String name) {
    return accumulators.getHistogram(requireNonNull(operatorName, UNSUPPORTED), name);
  }

  @Override
  public Timer getTimer(String name) {
    return accumulators.getTimer(name);
  }
}

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