stanfordnlp/CoreNLP · error · RuntimeException

Error occurred while constructing TreeReaderFactory: " + e

Error message

Error occurred while constructing TreeReaderFactory: " + e

What it means

TregexPattern.getTreeReaderFactory loads a custom TreeReaderFactory class by reflection from the -treeReaderFactory command-line option. If the class name cannot be found, instantiated, or cast to TreeReaderFactory, the raw reflective exception is wrapped in a RuntimeException and rethrown.

Solutions

1. Verify the fully-qualified class name passed to -treeReaderFactory is spelled correctly and the class implements edu.stanford.nlp.trees.TreeReaderFactory.
2. Ensure the jar/class file is on the runtime classpath (check with `java -cp ...` and try loading the class via Class.forName manually).
3. Confirm the class has a public no-argument constructor; add one if missing.
4. Inspect the nested exception `e` in the message (and its stack trace) to see the actual reflective failure cause.

Example fix

// before
java edu.stanford.nlp.trees.tregex.TregexPattern -treeReaderFactory MyFact treeFile
// after (correct, on-classpath class implementing TreeReaderFactory)
java -cp .:stanford-corenlp.jar edu.stanford.nlp.trees.tregex.TregexPattern -treeReaderFactory com.example.MyTreeReaderFactory treeFile

try {
  Class<?> c = Class.forName(factoryClassName);
  if (!TreeReaderFactory.class.isAssignableFrom(c)) throw new IllegalArgumentException(factoryClassName + " is not a TreeReaderFactory");
  c.getDeclaredConstructor().newInstance();
} catch (Exception e) {
  throw new IllegalArgumentException("Bad -treeReaderFactory class: " + factoryClassName, e);
}

static boolean isValidTreeReaderFactory(String name) {
  try {
    return Class.forName(name) != null && TreeReaderFactory.class.isAssignableFrom(Class.forName(name));
  } catch (Exception e) { return false; }
}

try {
  Treebank tb = ...; // runs with the custom factory
} catch (RuntimeException e) {
  if (e.getMessage() != null && e.getMessage().contains("constructing TreeReaderFactory")) {
    System.err.println("Fix -treeReaderFactory option: " + e.getCause());
  } else throw e;
}

When it happens

Trigger: Running the TregexPattern main() with -treeReaderFactory <className> where className is misspelled, not on the classpath, lacks a no-arg constructor, its constructor throws, or it does not implement TreeReaderFactory (ClassCastException).

Common situations: Typo in the fully-qualified class name; jar containing the custom factory not on the runtime classpath; factory class was refactored/renamed across versions; constructor requires arguments or throws during initialization.

Related errors

• Class is in classpath multiple times
• Could not set option
• Error loading flags.readerAndWriter
• Error loading flags.plainTextDocumentReaderAndWriter
• Unknown class

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/9ebf6abc3a9ac765. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/trees/tregex/TregexPattern.java:828

      }
      if (TRegexTreeVisitor.printNumMatchesToStdOut) {
        System.out.println(vis.numMatches());
      }
    } catch (IOException e) {
      log.warn(e);
    } catch (TregexParseException e) {
      errPW.println("Error parsing expression: " + args[0]);
      errPW.println("Parse exception: " + e);
    }
  }

  private static TreeReaderFactory getTreeReaderFactory(String treeReaderFactoryClassName) {
    TreeReaderFactory trf = new TRegexTreeReaderFactory();
    if (treeReaderFactoryClassName != null) {
      try {
        trf = (TreeReaderFactory) Class.forName(treeReaderFactoryClassName).getDeclaredConstructor().newInstance();
      } catch (Exception e) {
        throw new RuntimeException("Error occurred while constructing TreeReaderFactory: " + e);
      }
    }
    return trf;
  }

  private static Treebank treebank; // used by main method, must be accessible

  private static final long serialVersionUID = 5060298043763944913L;


  // not thread-safe, but only used by TregexPattern's main method
  private static class TRegexTreeVisitor implements TreeVisitor {

    private static boolean printNumMatchesToStdOut = false;
    static boolean printNonMatchingTrees = false;
    static boolean printSubtreeCode = false;
    static boolean printTree = false;
    static boolean printWholeTreeOnly = false;

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