stanfordnlp/CoreNLP · error · RuntimeIOException

Serializing classifier to

Error message

Serializing classifier to 

What it means

When serializeClassifierToString / the serializePath path fails (any Exception from opening the output stream or serializing the classifier), CRFClassifier wraps the cause in a RuntimeIOException with message 'Serializing classifier to <path>... FAILED'. The saved snippet shows the success log; the throw is the failure branch of the same call.

Solutions

1. Ensure the serializeTo target's parent directory exists and is writable (mkdir -p, chmod).
2. Check the serializePath string format expected by IOUtils.writeStreamFromString (plain file path, or qualified with a supported handler prefix).
3. Read the chained cause exception (e.getCause()) to see the underlying IOException and fix it (permissions, disk space).
4. Verify disk space/quota before serializing large CRF models.
5. Call serializeClassifier(OutputStream) directly with your own FileOutputStream to get clearer IO errors.

Example fix

// before
props.setProperty("serializeTo", "models/mycrf.ser.gz"); // models/ missing -> RuntimeIOException
// after
new File("models").mkdirs();
props.setProperty("serializeTo", "models/mycrf.ser.gz");

File out = new File(serializePath);
if (out.getParentFile() != null && !out.getParentFile().canWrite())
  throw new IOException("Cannot write to " + out.getParentFile());
if (out.getParentFile() != null) out.getParentFile().mkdirs();
if (new File(serializePath).getUsableSpace() < 1_000_000_000L) throw new IOException("Low disk space");

try {
  crf.serializeClassifierToString(serializePath);
} catch (RuntimeIOException e) {
  Throwable cause = e.getCause();
  log.error("Serialization failed for " + serializePath + ": " + cause, cause);
  throw e;
}

When it happens

Trigger: Calling serializeClassifierToString(serializePath) or flags.serializeTo with a path/filename spec IOUtils cannot open (bad URL/file form, unwritable directory, nonexistent parent dir, invalid endpoint), or when serializeClassifier itself throws during object graph writing.

Common situations: Output directory does not exist or is not writable; serializeTo path uses an unsupported protocol string; disk full; serialization fails on a non-serializable component; running under a user without write permission.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• RuntimeIOException wrapping IOException
• Error creating data exporter
• Failed to save classifier
• Could not open temporary feature index file for reading.
• Failed to load segmenter

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/1bf7ad5c9809f5e9. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/crf/CRFClassifier.java:2497

    }

    return f;
  }


  /**
   * {@inheritDoc}
   */
  @Override
  public void serializeClassifier(String serializePath) {
    ObjectOutputStream oos = null;
    try {
      oos = IOUtils.writeStreamFromString(serializePath);
      serializeClassifier(oos);
      log.info("Serializing classifier to " + serializePath + "... done.");

    } catch (Exception e) {
      throw new RuntimeIOException("Serializing classifier to " + serializePath + "... FAILED", e);
    } finally {
      IOUtils.closeIgnoringExceptions(oos);
    }
  }

  /**
   * Serialize the classifier to the given ObjectOutputStream.
   * <br>
   * (Since the classifier is a processor, we don't want to serialize the
   * whole classifier but just the data that represents a classifier model.)
   */
  @Override
  public void serializeClassifier(ObjectOutputStream oos) {
    try {
      oos.writeObject(labelIndices);
      oos.writeObject(classIndex);
      oos.writeObject(featureIndex);
      oos.writeObject(flags);

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