OpenAPITools/openapi-generator · error · UnsupportedOperationException

Not implemented

Error message

Not implemented

What it means

JavaHelidonServerCodegen deliberately overrides setPerformBeanValidation to throw UnsupportedOperationException, because the Helidon server templates never implemented bean-validation generation. The override fires when performBeanValidation resolves to true via additionalProperties (convertPropertyToBooleanAndWriteBack) or when user code calls the setter — it fails regardless of the boolean's value if invoked programmatically, though config-driven generation only trips it when the property is set truthy.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaHelidonServerCodegen.java:474

    @Override
    public CodegenType getTag() {
        return CodegenType.SERVER;
    }

    @Override
    public String getName() {
        return "java-helidon-server";
    }

    @Override
    public String getHelp() {
        return "Generates a Java Helidon Server application.";
    }

    @Override
    public void setPerformBeanValidation(boolean performBeanValidation) {
        throw new UnsupportedOperationException("Not implemented");
    }

    public void setSerializationLibrary(String serializationLibrary) {
        if (SERIALIZATION_LIBRARY_JACKSON.equalsIgnoreCase(serializationLibrary)) {
            this.serializationLibrary = SERIALIZATION_LIBRARY_JACKSON;
            this.jackson = true;
        } else if (SERIALIZATION_LIBRARY_JSONB.equalsIgnoreCase(serializationLibrary)) {
            this.serializationLibrary = SERIALIZATION_LIBRARY_JSONB;
            this.jackson = false;
        } else {
            throw new IllegalArgumentException("Unexpected serializationLibrary value: " + serializationLibrary);
        }
    }

    /**
     * Check if pom file and src directory already exist.
     *
     * @return outcome of test

View on GitHub (pinned to fcec517be3)

Solutions

1. Remove performBeanValidation from the additionalProperties/config for java-helidon-server
2. If bean validation is mandatory, add @Valid/@NotNull manually to generated interfaces, or switch to a generator that supports it (spring, jaxrs-jersey)
3. When embedding, never call setPerformBeanValidation on this generator — it is intentionally unimplemented
4. Diff your shared config against `config-help -g java-helidon-server` output before applying it to a new generator

Example fix

# before
openapi-generator-cli generate -g java-helidon-server -i api.yaml \
  --additional-properties performBeanValidation=true

# after
openapi-generator-cli generate -g java-helidon-server -i api.yaml \
  --additional-properties useBeanValidation=true   # supported alternative for model validation

// java-helidon-server does not implement performBeanValidation
if (Boolean.parseBoolean(String.valueOf(opts.getOrDefault("performBeanValidation", "false")))) {
    throw new UnsupportedOperationException("performBeanValidation is not implemented by java-helidon-server; remove the option");
}

try {
    generator.generate();
} catch (UnsupportedOperationException e) {
    // deliberate 'Not implemented' guard — strip the unsupported option and rerun, do not retry as-is
    if ("Not implemented".equals(e.getMessage())) {
        opts.remove("performBeanValidation");
        generator.generate(); // one sanitized retry
    } else throw e;
}

When it happens

Trigger: Passing --additional-properties performBeanValidation=true with -g java-helidon-server. Reusing a config file built for spring or jaxrs generators where bean validation is supported. Embedding the generator and calling new JavaHelidonServerCodegen().setPerformBeanValidation(...) directly.

Common situations: Organizations with a house-style config enabling bean validation across all Java server generators apply it to Helidon too. Developers porting from -g spring or -g jaxrs-jersey carry the option over without checking the Helidon generator's support matrix.

Related errors

• Unexpected serializationLibrary value: {serializationLibrary
• Both %s and %s properties were set with different value.
• Helidon version %s uses the %s namespace but options specifi
• Helidon version %s uses the %s prefix for EE dependencies bu
• Unknown library option %s for Helidon Server

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/be28500c317213c6. Report an issue: GitHub.