GoogleContainerTools/jib · warning

Invalid class file found: ${file}

Error message

Invalid class file found: ${file}

What it means

During main class discovery, Jib parses each candidate .class file with ASM's ClassReader; when the bytes are not a valid class file (ASM throws ArrayIndexOutOfBoundsException), Jib logs this warning and skips the file instead of failing the build.

Source

Thrown at jib-core/src/main/java/com/google/cloud/tools/jib/api/MainClassFinder.java:242

      MainClassVisitor mainClassVisitor = new MainClassVisitor();
      try (InputStream classFileInputStream = Files.newInputStream(file)) {
        ClassReader reader = new ClassReader(classFileInputStream);
        reader.accept(mainClassVisitor, 0);
        if (mainClassVisitor.visitedMainClass) {
          mainClasses.add(reader.getClassName().replace('/', '.'));
        }

      } catch (IllegalArgumentException ex) {
        throw new UnsupportedOperationException(
            "Check the full stace trace, and if the root cause is from ASM ClassReader about "
                + "unsupported class file version, see "
                + "https://github.com/GoogleContainerTools/jib/blob/master/docs/faq.md"
                + "#i-am-seeing-unsupported-class-file-major-version-when-building",
            ex);

      } catch (ArrayIndexOutOfBoundsException ignored) {
        // Not a valid class file (thrown by ClassReader if it reads an invalid format)
        logger.accept(LogEvent.warn("Invalid class file found: " + file));

      } catch (IOException ignored) {
        // Could not read class file.
        logger.accept(LogEvent.warn("Could not read file: " + file));
      }
    }

    if (mainClasses.size() == 1) {
      // Valid class found.
      return Result.success(mainClasses.get(0));
    }
    if (mainClasses.isEmpty()) {
      // No main class found anywhere.
      return Result.mainClassNotFound();
    }
    // More than one main class found.
    return Result.multipleMainClasses(mainClasses);
  }

View on GitHub (pinned to fb949e2676)

Solutions

1. Run a clean rebuild (mvn clean install / gradle clean build) to remove corrupted class files
2. Locate and inspect the offending file named in the warning; delete or fix it
3. Ensure only compiled Java classes are in the classes output directory

Example fix

// before (shell)
# build has stale/corrupt target/classes/foo.class
mvn jib:build
// after
mvn clean jib:build

// Verify class files are readable valid JVM class files before building
byte[] bytes = java.nio.file.Files.readAllBytes(path);
if (bytes.length < 8 || (bytes[0] & 0xFF) != 0xCA || (bytes[1] & 0xFF) != 0xFE)
  System.err.println("Not a valid class file: " + path);

When it happens

Trigger: MainClassFinder.find() iterates class files in the classes directory; reading a file whose content is not a valid JVM class file format (corrupted build output, a non-class file with .class extension, truncated/incompatible class version handled elsewhere) triggers the catch (ArrayIndexOutOfBoundsException) branch.

Common situations: Interrupted compilations leaving truncated .class files; resource files accidentally named *.class; stale classes from a different JDK being read by incompatible tooling.

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

• The class file (${jarEntry}) is of an invalid format.
• Reached end of class file (${jarEntry}) before being able to
• error running extension '<extensionClassName>': <message>
• Failed to generate a Jib file map for sync with Skaffold
• No classes files were found - did you compile your project?

AI-assisted analysis of GoogleContainerTools/jib@fb949e2676 (2026-09-06). Data as JSON: /api/errors/b19570d28f3b7ba3. Report an issue: GitHub.