stanfordnlp/CoreNLP · error · IOException

Unable to open " " as class path, filename or URL

Error message

Unable to open "${textFileOrUrl}" as class path, filename or URL

What it means

After trying classpath, filesystem, and URL resolution, getInputStreamFromURLOrClasspathOrFileSystem gives up and throws IOException 'Unable to open "<name>" as class path, filename or URL'. All three resolution strategies failed, so the resource is unreachable by any supported means.

Solutions

Check the file exists at the literal path (ls) or add its directory/jar to the classpath (-cp).
If it's a classpath resource, verify it's inside the JAR (jar tf app.jar | grep name) and the path has no leading slash mistakes.
If it's a URL, verify the scheme/host with curl and correct typos.
Ensure model/resource files are downloaded or added as a Maven/Gradle dependency before running.

Example fix

// before
props.load(IOUtils.readerFromString("StanfordCoreNLP-chinese.properties")); // not on classpath
// after
File p = new File("conf/StanfordCoreNLP-chinese.properties");
if (!p.exists()) throw new FileNotFoundException(p.getAbsolutePath());
props.load(IOUtils.readerFromString(p.getAbsolutePath()));

Defensive patterns

Strategy: try-catch

Validate before calling

File f = new File(name);
if (!f.exists() && IOUtils.class.getResourceAsStream(name.startsWith("/") ? name : "/" + name) == null) {
  throw new FileNotFoundException(name + " is neither a file nor a classpath resource");
}

Try / catch

try {
  InputStream in = IOUtils.getInputStreamFromURLOrClasspathOrFileSystem(name);
} catch (IOException e) {
  if (e.getMessage().startsWith("Unable to open")) {
    log.severe("Resource not found as classpath/file/URL: " + name);
  }
}

Prevention

Package resources in the JAR and verify with jar tf
Add model jars to the classpath
Validate URLs with curl before use
Run from the intended working directory

When it happens

Trigger: The string is not a valid URL, is not on the classpath, and is not an existing file: wrong filename, resource not packaged in the JAR, typo'd URL scheme, or file deleted/not downloaded.

Common situations: Missing model files (e.g. CoreNLP models jar not on classpath); running from a different working directory than expected; resource present in sources but not copied into the built artifact; HTTPS URL with scheme typo (htp://).

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/cec309672dc9eff2. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/io/IOUtils.java:501

    InputStream in;
    if (textFileOrUrl == null) {
      throw new NullPointerException("Attempt to open file with null name");
    } else if (textFileOrUrl.matches("https?://.*")) {
      URL u = new URL(textFileOrUrl);
      URLConnection uc = u.openConnection();
      in = uc.getInputStream();
    } else {
      try {
        in = findStreamInClasspathOrFileSystem(textFileOrUrl);
      } catch (FileNotFoundException e) {
        try {
          // Maybe this happens to be some other format of URL?
          URL u = new URL(textFileOrUrl);
          URLConnection uc = u.openConnection();
          in = uc.getInputStream();
        } catch (IOException e2) {
          // Don't make the original exception a cause, since it is usually bogus
          throw new IOException("Unable to open \"" +
                  textFileOrUrl + "\" as " + "class path, filename or URL"); // , e2);
        }
      }
    }

    // If it is a GZIP stream then ungzip it
    if (textFileOrUrl.endsWith(".gz")) {
      try {
        in = new GZIPInputStream(in);
      } catch (Exception e) {
        throw new RuntimeIOException("Resource or file looks like a gzip file, but is not: " + textFileOrUrl, e);
      }
    }

    // buffer this stream.  even gzip streams benefit from buffering,
    // such as for the shift reduce parser [cdm 2016: I think this is only because default buffer is small; see below]
    in = new BufferedInputStream(in);

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