stanfordnlp/CoreNLP · warning

Could not open jar file:

Error message

Could not open jar file: 

What it means

getVisibleClasses() opens each jar with a JarFile to enumerate entries. If the jar cannot be opened as a zip (IOException - missing, empty, or corrupt file, or a path that is not a jar), it logs 'Could not open jar file: <f> (are you sure the file exists?)' and moves on to the next jar. No classes from that jar are registered.

Solutions

1. Verify the file exists and is a valid zip: `unzip -t <file>.jar` or `file <f>`
2. Re-download or rebuild the corrupted jar (e.g. `mvn dependency:purge-local-repository`)
3. Remove empty/placeholder files from the scanned jar directory
4. Check disk space and filesystem health if many jars fail at once

Example fix

# before: scan dir contains truncated jar
# after: verify and replace
unzip -t mylib.jar || (rm mylib.jar && mvn dependency:copy -Dartifact=com.example:mylib:1.0)

File f = new File(jarPath);
if (!f.isFile() || f.length() == 0) throw new IllegalArgumentException("Not a readable jar: " + f);
try (java.util.zip.ZipFile zf = new java.util.zip.ZipFile(f)) {
    if (zf.size() == 0) throw new IllegalArgumentException("Empty/corrupt jar: " + f);
} catch (java.io.IOException e) {
    throw new IllegalArgumentException("Corrupt jar: " + f, e);
}

When it happens

Trigger: Passing a directory to ArgumentParser class discovery where an entry is a zero-byte, truncated (interrupted download), corrupted, or non-zip file with a .jar extension, or a file deleted between listing and opening.

Common situations: Partially downloaded Maven jars; jars corrupted by filesystem issues or interrupted builds; directories containing placeholder/LFS pointer files instead of real jars; wrong directory passed to the scan.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

• argsToProperties could not read properties file: " + file
• Cannot find or open + sentFileName
• Could not create directory <tgtDir.getAbsolutePath()>, as a…
• Could not create directory <tgtDir.getAbsolutePath()>
• Could not open temporary feature index file for reading.

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/f1045114a48955bc. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/ArgumentParser.java:267

            if (clazz.matches(".*class$")) {
              //(if it's a class)
              clazz = clazz.substring(0, clazz.length() - 6)
                  .replaceAll("/", ".");
              //(add it)
              try {
                classes.add(
                    Class.forName(clazz,
                        false,
                        ClassLoader.getSystemClassLoader()));
              } catch (ClassNotFoundException ex) {
                warn("Could not load class in jar: " + f + " at path: " + clazz);
              } catch (NoClassDefFoundError ex) {
                debug("Could not scan class: " + clazz + " (in jar: " + f + ')');
              }
            }
          }
        } catch (IOException e) {
          warn("Could not open jar file: " + f + "(are you sure the file exists?)");
        }
      } else {
        //case: ignored jar
      }
    }

    return classes.toArray(new Class<?>[classes.size()]);
  }

  /**
   * Get all the declared fields of this class and all super classes.
   */
  private static Field[] scrapeFields(Class<?> clazz) throws Exception {
    List<Field> fields = new ArrayList<>();
    while (clazz != null && !clazz.equals(Object.class)) {
      fields.addAll(Arrays.asList(clazz.getDeclaredFields()));
      clazz = clazz.getSuperclass();
    }

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