stanfordnlp/CoreNLP · error · ClassCastException

Wanted LexicalizedParser, got

Error message

Wanted LexicalizedParser, got 

What it means

loadModel(ObjectInputStream) reads one object and expects it to be a LexicalizedParser; anything else is rejected with this ClassCastException naming the actual class received. It also converts IOException/ClassNotFoundException from stream deserialization into RuntimeIOException/RuntimeException.

Solutions

1. Point loadModel at a file that contains a serialized LexicalizedParser (created via saveParserToSerializedFile).
2. Check the actual class named in the message and use the matching load API (e.g. loadParserQuery).
3. Use LexicalizedParser.loadModel(String) so the correct loading path is chosen for the file.

Example fix

// before
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("query.ser"));
LexicalizedParser lp = LexicalizedParser.loadModel(ois); // file is a query
// after
LexicalizedParser lp = LexicalizedParser.loadModel("parser.ser.gz");

if (o instanceof LexicalizedParser) { LexicalizedParser lp = (LexicalizedParser) o; }

try { parser = LexicalizedParser.loadModel(path); } catch (ClassCastException | RuntimeIOException | RuntimeException e) { log.error("Not a serialized parser model: " + e.getMessage()); }

When it happens

Trigger: Calling LexicalizedParser.loadModel(ObjectInputStream) on a stream whose next object is not a parser — e.g. the file holds a LexicalizedParserQuery, an Options object, or unrelated serialized data.

Common situations: Deserializing a file saved with parserQuery/other components, or reading a file produced by an incompatible library version where class layout differs.

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

• Classifier class casting problem.
• Expected tagged words
• This evaluator only works for the ShiftReduceParser
• This evaluator only works for the ShiftReduceParser
• addFeature was called with a features object that is…

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/514d3d452fb3dae3. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/parser/lexparser/LexicalizedParser.java:202

    LexicalizedParser parser = getParserFromFile(parserFileOrUrl, op);
    if (extraFlags.length > 0) {
      parser.setOptionFlags(extraFlags);
    }
    return parser;
  }

  /**
   * Reads one object from the given ObjectInputStream, which is
   * assumed to be a LexicalizedParser.  Throws a ClassCastException
   * if this is not true.  The stream is not closed.
   */
  public static LexicalizedParser loadModel(ObjectInputStream ois) {
    try {
      Object o = ois.readObject();
      if (o instanceof LexicalizedParser) {
        return (LexicalizedParser) o;
      }
      throw new ClassCastException("Wanted LexicalizedParser, got " +
                                   o.getClass());
    } catch (IOException e) {
      throw new RuntimeIOException(e);
    } catch (ClassNotFoundException e) {
      throw new RuntimeException(e);
    }
  }

  public static LexicalizedParser copyLexicalizedParser(LexicalizedParser parser) {
    return new LexicalizedParser(parser.lex, parser.bg, parser.ug, parser.dg, parser.stateIndex, parser.wordIndex, parser.tagIndex, parser.op);
  }

  public LexicalizedParser(Lexicon lex, BinaryGrammar bg, UnaryGrammar ug, DependencyGrammar dg, Index<String> stateIndex, Index<String> wordIndex, Index<String> tagIndex, Options op) {
    this.lex = lex;
    this.bg = bg;
    this.ug = ug;
    this.dg = dg;
    this.stateIndex = stateIndex;

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