stanfordnlp/CoreNLP · error · RuntimeIOException

Failed to save classifier

Error message

Failed to save classifier

What it means

serializeClassifier(String) opens an output stream via IOUtils.writeStreamFromString and writes the combined classifier. Any failure during opening the stream or writing the model is wrapped as a RuntimeIOException with this message.

Solutions

1. Create parent directories before serializing: new File(path).getParentFile().mkdirs()
2. Verify write permission on the target path for the running user
3. Serialize to a local writable path first, then copy to the final destination
4. Check the wrapped cause for the underlying IO failure

Example fix

// before
classifier.serializeClassifier("out/models/model.ser.gz"); // RuntimeIOException if out/models missing
// after
new File("out/models").mkdirs();
classifier.serializeClassifier("out/models/model.ser.gz");

File out = new File(path);
File parent = out.getParentFile();
if (parent != null && !parent.isDirectory() && !parent.mkdirs())
  throw new IllegalStateException("cannot create dir " + parent);
if (parent != null && !parent.canWrite()) throw new IllegalStateException("not writable: " + parent);

try {
  classifier.serializeClassifier(serializePath);
} catch (RuntimeIOException e) {
  log.error("model save failed", e.getCause());
  throw e;
}

When it happens

Trigger: Calling classifier.serializeClassifier("/bad/dir/model.ser.gz") where the target directory does not exist, is not writable, or the path string is not a valid filename/URL for IOUtils.writeStreamFromString.

Common situations: Writing to a read-only deployment directory; missing parent directories; running under a user without write permission; disk full during model dump.

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
• RuntimeException with no message (model write failure)
• Serializing classifier to
• ERROR: Invalid dependency node line

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/7b53cac329bdaaeb. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/ClassifierCombiner.java:504

  @Override
  public void train(Collection<List<IN>> docs,
                    DocumentReaderAndWriter<IN> readerAndWriter) {
    throw new UnsupportedOperationException();
  }

  // write a ClassifierCombiner to disk, this is based on CRFClassifier code
  @Override
  public void serializeClassifier(String serializePath) {
    log.info("Serializing classifier to " + serializePath + "...");

    ObjectOutputStream oos = null;
    try {
      oos = IOUtils.writeStreamFromString(serializePath);
      serializeClassifier(oos);
      log.info("done.");

    } catch (Exception e) {
      throw new RuntimeIOException("Failed to save classifier", e);
    } finally {
      IOUtils.closeIgnoringExceptions(oos);
    }
  }

  // method for writing a ClassifierCombiner to an ObjectOutputStream
  @Override
  public void serializeClassifier(ObjectOutputStream oos) {
    try {
      // record the properties used to initialize
      oos.writeObject(initProps);
      // this is a bit of a hack, but have to write this twice so you can get it again
      // after you initialize AbstractSequenceClassifier
      // basically when this is read from the ObjectInputStream, I read it once to call
      // super(props) and then I read it again so I can set this.initProps
      // TODO: probably should have AbstractSequenceClassifier store initProps to get rid of this double writing
      oos.writeObject(initProps);
      // record the initial loadPaths

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