stanfordnlp/CoreNLP · error · ReflectionLoadingException

Error creating " + className

Error message

Error creating " + className

What it means

ReflectionLoading.loadByReflection instantiates a class by name via MetaClass and wraps any failure (class not found, constructor mismatch, exception thrown in constructor) into a ReflectionLoadingException with the message 'Error creating <className>'. It is a uniform wrapper for reflection-based object creation used throughout Stanford NLP.

Solutions

1. Verify the fully-qualified class name in your config and that its jar is on the classpath
2. Check the class has a public constructor matching the arguments you pass
3. Inspect the cause (getCause()) of the ReflectionLoadingException for the underlying ClassNotFoundException or constructor error

Example fix

// before
MyTokenizer t = ReflectionLoading.loadByReflection("edu.stanford.nlp.process.MyTokenzier"); // typo
// after
MyTokenizer t = ReflectionLoading.loadByReflection("edu.stanford.nlp.process.MyTokenizer");

String name = "edu.stanford.nlp.process.MyTokenizer";
try { Class.forName(name); } catch (ClassNotFoundException e) { /* fix name/classpath before calling */ }

try {
  T obj = ReflectionLoading.loadByReflection(className, args);
} catch (ReflectionLoadingException e) {
  log.error("Cannot create " + className + ": " + e.getCause());
  throw e;
}

When it happens

Trigger: Calling ReflectionLoading.loadByReflection("com.example.Foo", args...) when the class name is misspelled, the class is not on the classpath, no matching constructor exists for the arguments, or the constructor itself throws.

Common situations: Configuring a custom tokenizer, parser, or annotator class via a string property with a typo or wrong package; dependency jar missing at runtime so the class can't load; constructor signature changed between versions while a config file still lists old arguments.

Related errors

• Class at path
• Error getting field value for
• Cannot get field from
• Loading: failed with
• Couldn't create POS tagger extractor class

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/1a732b8cdd245e63. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/ReflectionLoading.java:38

   * <br>
   *  {@code String s = ReflectionLoading.loadByReflection("java.lang.String", "foo"); }
   * <br>
   *  {@code String s = ReflectionLoading.loadByReflection("java.lang.String"); }
   * <br>
   * Note that this uses generics for convenience, but this does
   * nothing for compile-time error checking.  You can do:
   * <br>
   *  {@code Integer i = ReflectionLoading.loadByReflection("java.lang.String"); }
   * <br>
   * and it will compile just fine, but will result in a ClassCastException.
   */
  @SuppressWarnings("unchecked")
  public static <T> T loadByReflection(String className,
                                       Object ... arguments) {
    try{
      return (T) new MetaClass(className).createInstance(arguments);
    } catch (Exception e) {
      throw new ReflectionLoadingException("Error creating " + className, e);
    }
  }

  /**
   * This class encapsulates all of the exceptions that can be thrown
   * when loading something by reflection.
   */
  public static class ReflectionLoadingException extends RuntimeException {

    private static final long serialVersionUID = -3324911744277952585L;


    public ReflectionLoadingException(String message, Throwable reason) {
      super(message, reason);
    }

  }

View on GitHub (pinned to 1b7edd19c4)