Java is not available because the feature is not enabled

Error message

Java is not available because the feature is not enabled

What it means

Java script execution is an optional cargo feature (`java`) in Windmill. If a job for a Java script reaches a worker binary compiled without that feature, the executor returns this error before attempting any run, because the JVM integration is not linked into the binary.

Source

Thrown at backend/windmill-worker/src/worker.rs:6758

                    job,
                    conn,
                    client,
                    parent_runnable_path,
                    inner_content: &code,
                    job_dir,
                    requirements_o: lock.as_ref(),
                    shared_mount: &shared_mount,
                    base_internal_url,
                    worker_name,
                    envs,
                    occupancy_metrics,
                }))
                .await
            }
        }
        ScriptLang::Java => {
            #[cfg(not(feature = "java"))]
            return Err(anyhow::anyhow!(
                "Java is not available because the feature is not enabled"
            )
            .into());

            #[cfg(feature = "java")]
            {
                if run_inline {
                    return Err(Error::internal_err(
                        "Inline execution is not yet supported for this language".to_string(),
                    ));
                }
                Box::pin(handle_java_job(JobHandlerInputJava {
                    mem_peak,
                    canceled_by,
                    job,
                    conn,
                    client,
                    parent_runnable_path,

View on GitHub (pinned to e474e8803c)

Solutions

Rebuild the worker with `--features java` included
Deploy a worker image with Java support and route java jobs to it via tags
Rewrite the script in a supported language if Java is not required

Example fix

// before
cargo run --features quickjs
// after
cargo run --features quickjs,java

Defensive patterns

Strategy: fallback

Try / catch

try {
  await runScript("java", code);
} catch (e) {
  if (String(e).includes("Java is not available")) {
    // rebuild with --features java or reroute to a java-enabled worker
  }
}

Prevention

Include `java` in the worker's --features for any workspace using Java scripts
Keep a feature checklist per deployed worker image
Route language-specific jobs to matching worker tags

When it happens

Trigger: Dispatching a script with language `java` to a worker built without `--features java` (default dev build, minimal self-hosted build, or an image variant without Java support).

Common situations: Default `cargo run` dev backends, slim Docker images, workspaces where Java scripts exist but no java-enabled worker is deployed.

Related errors

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/2df56524072dda0d. Report an issue: GitHub.