stanfordnlp/CoreNLP · error · UnsupportedOperationException

Can only parse raw text if a tagger is specified, as the…

Error message

Can only parse raw text if a tagger is specified, as the ShiftReduceParser cannot produce its own tags

What it means

ShiftReduceParser.parse(String) accepts raw (untagged) text, but the parser cannot POS-tag sentences itself; it requires pre-tagged input. If the test option preTag is false — meaning no tagger was configured — calling the String overload cannot proceed and throws UnsupportedOperationException.

Solutions

Tag the sentence yourself and call parse(List<? extends HasWord>) with CoreLabels carrying tags
Load/parser-config with a tagger so preTag is enabled (e.g. specify -testOptions preTag with a tagger serialized path)
Use a parser model serialized together with its tagger

Example fix

// before
Tree t = parser.parse("The dog barked");

// after
List<CoreLabel> tagged = tokenizerFactory.getTokenizer(new StringReader("The dog barked")).tokenize();
// ... set tags via a tagger ...
Tree t = parser.parse(tagged);

Defensive patterns

Strategy: type-guard

Validate before calling

if (!parser.getOp().testOptions.preTag) {
  throw new IllegalStateException("Supply tagged List<HasWord> instead of raw text");
}

Try / catch

try {
  return parser.parse(rawSentence);
} catch (UnsupportedOperationException e) {
  return parser.parse(tagger.apply(tokenize(rawSentence)));
}

Prevention

Always call the List<HasWord> overload unless the model bundles a tagger
Check testOptions.preTag at pipeline startup
Bundle the tagger with the serialized parser model

When it happens

Trigger: Calling parser.parse("some raw sentence") on a parser model loaded without a tagger (op.testOptions.preTag == false).

Common situations: Loading a serialized ShiftReduceParser model trained without a POS tagger and passing plain text; upgrading models or switching from a parser+tagger bundle to a bare parser while keeping raw-text call sites.

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

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/8c2c66a2f95033e9. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/parser/shiftreduce/ShiftReduceParser.java:176

  /** Return the Set of POS tags used in the model. */
  public Set<String> tagSet() {
    return model.tagSet();
  }

  @Override
  public boolean requiresTags() {
    return true;
  }

  @Override
  public ParserQuery parserQuery() {
    return new ShiftReduceParserQuery(this);
  }

  @Override
  public Tree parse(String sentence) {
    if (!getOp().testOptions.preTag) {
      throw new UnsupportedOperationException("Can only parse raw text if a tagger is specified, as the ShiftReduceParser cannot produce its own tags");
    }
    return super.parse(sentence);
  }

  @Override
  public Tree parse(List<? extends HasWord> sentence) {
    ShiftReduceParserQuery pq = new ShiftReduceParserQuery(this);
    if (pq.parse(sentence)) {
      return pq.getBestParse();
    }
    return ParserUtils.xTree(sentence);
  }

  @Override
  public Tree parseTree(List<? extends HasWord> sentence) {
    ShiftReduceParserQuery pq = new ShiftReduceParserQuery(this);
    if (pq.parse(sentence)) {
      return pq.getBestParse();

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