stanfordnlp/CoreNLP · warning

Could not read Regex mapping

Error message

Could not read Regex mapping: ${mappingFile}

What it means

readRegexnerGazette loads a TSV regexner mapping file line by line (key TAB target). The file could not be read (missing path, unreadable, or IO problem), so the parser logs a warning and returns whatever partial map was accumulated (possibly empty). This is non-fatal by design: the NER pipeline continues with fewer/no regexner entries.

Solutions

1. Verify the regexner.mapping path exists and is readable from the process working directory (ls -l the file).
2. Use an absolute path or a classpath-qualified resource URL in the ner.regexner.mapping property.
3. Check file permissions and that the user running the JVM can read it.
4. If intentional absence, silence is fine — but confirm the map contents by logging mapping.size() and ensure downstream NER quality is acceptable.

Example fix

// before
ner.regexner.mapping=gazetteers/regexner.txt
// after
ner.regexner.mapping=/absolute/path/to/gazetteers/regexner.txt

File f = new File(mappingPath);
if (!f.isFile() || !f.canRead()) {
  throw new IllegalArgumentException("regexner mapping not readable: " + mappingPath);
}

try {
  Map<String,String> m = readRegexnerGazette(path);
  if (m.isEmpty()) log.warn("regexner map empty — check path " + path);
} catch (IOException e) {
  log.warn("falling back to default gazetteer", e);
}

When it happens

Trigger: Calling NERClassifierCombiner setup with a regexner.mapping property pointing to a nonexistent, unreadable, or empty file; or a file with a bad encoding/unreadable permissions that throws IOException during readLines.

Common situations: Relative path resolved against the wrong working directory when launching from an IDE or service; model jar path typo (resource inside jar not addressable as a file path); file deleted after config was written.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• Error reading threshold file
• TokensRegexNERAnnotator
• Unknown default unit
• Error loading classifier from
• edu.stanford.nlp.io.RuntimeIOException

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/70baa12c7b48f86e. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/NERClassifierCombiner.java:403

  /**
   * Read a gazette mapping in TokensRegex format from the given path
   * The format is: 'case_sensitive_word \t target_ner_class' (additional info is ignored).
   *
   * @param mappingFile The mapping file to read from, as a path either on the filesystem or in your classpath.
   *
   * @return The mapping from word to NER tag.
   */
  private static Map<String, String> readRegexnerGazette(String mappingFile) {
    Map<String, String> mapping = new HashMap<>();
    try (BufferedReader reader = IOUtils.readerFromString(mappingFile.trim())){
      for (String line : IOUtils.slurpReader(reader).split("\n")) {
        String[] fields = line.split("\t");
        String key = fields[0];
        String target = fields[1];
        mapping.put(key, target);
      }
    } catch (IOException e) {
      log.warn("Could not read Regex mapping: " + mappingFile);
    }
    return Collections.unmodifiableMap(mapping);
  }



  /** The main method. */
  public static void main(String[] args) throws Exception {
    StringUtils.logInvocationString(log, args);
    Properties props = StringUtils.argsToProperties(args);
    SeqClassifierFlags flags = new SeqClassifierFlags(props, false); // false for print probs as printed in next code block

    String loadPath = props.getProperty("loadClassifier");
    NERClassifierCombiner ncc;
    if (loadPath != null) {
      // note that when loading a serialized classifier, the philosophy is override
      // any settings in props with those given in the commandline
      // so if you dumped it with useSUTime = false, and you say -useSUTime at

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