apache/druid · critical · java.lang.UnsupportedOperationException

Unable to define specialized class:

Error message

Unable to define specialized class: 

What it means

DefineClassUtils.defineClass invokes the cached JDK internal defineClass MethodHandle with invokeExact. If the invocation itself fails for any reason ( IllegalAccess, IllegalCallerException, LinkageError, class file errors), it wraps the cause in an UnsupportedOperationException with this message.

Solutions

1. Read the cause ('Caused by') to identify whether it is access control or bytecode corruption
2. Add the required JVM flags (e.g. --add-opens java.base/java.lang=ALL-UNNAMED) when running on JDK 9+
3. Ensure the target class's package is opened/exported to the Druid module performing the definition
4. Verify the generated bytecode matches the target class's classloader/version expectations

Example fix

// JVM launch flags
// before: java -jar druid.jar
// after:  java --add-opens java.base/java.lang=ALL-UNNAMED -jar druid.jar

// preflight: attempt resolving the internal API
// (no public precheck besides isDefineClassSupported)
boolean handleResolvable = DefineClassUtils.isDefineClassSupported();

try {
  return DefineClassUtils.defineClass(targetClass, byteCode, className);
} catch (UnsupportedOperationException e) {
  Throwable cause = e.getCause();
  log.error(e, "defineClass invoke failed: %s", cause == null ? "unknown" : cause.getClass());
  throw new RuntimeException("Class definition failed; check --add-opens flags", e);
}

When it happens

Trigger: DEFINE_CLASS.invokeExact(targetClass, byteCode, className) throws a Throwable — e.g. the caller module lacks the lookup/access rights, the bytecode is invalid, a LinkageError occurs, or the JVM restricts defineClass even though the handle exists.

Common situations: Running on JDK 9+ without --add-opens/--add-exports for internal APIs; defining a class into a package that is not open to Druid's module; malformed generated bytecode.

Understand the failure class

Background: "unsupported platform" / "not supported on this platform" errors: what they mean and how to fix them — this error's family across 47 libraries.

Related errors

• DEFINE_CLASS_NOT_SUPPORTED_EXCEPTION
• Cannot determine maxDirectMemory from
• CLEANER_NOT_SUPPORTED_EXCEPTION
• Cleaning is not support on this platform, because internal…
• No VM class, cannot do memory check.

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/80c89f6dda733e26. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/java/util/common/DefineClassUtils.java:107

  public static Class defineClass(
      Class<?> targetClass,
      byte[] byteCode,
      String className
  )
  {
    if (DEFINE_CLASS == null) {
      throw new UnsupportedOperationException(
          "defineClass is not supported on this platform, "
          + "because internal Java APIs are not compatible with this Druid version",
          DEFINE_CLASS_NOT_SUPPORTED_EXCEPTION
      );
    }

    try {
      return (Class) DEFINE_CLASS.invokeExact(targetClass, byteCode, className);
    }
    catch (Throwable t) {
      throw new UnsupportedOperationException("Unable to define specialized class: " + className, t);
    }
  }
}

View on GitHub (pinned to 9b90983fd2)