What causes "Build tool "{buildTool}" is not supported or misspelled." in OpenAPITools/openapi-generator?

Use exactly one of: buildTool=gradle, buildTool=maven, or buildTool=all

OpenAPITools/openapi-generator · error · RuntimeException

Build tool "{buildTool}" is not supported or misspelled.

Error message

Build tool "{buildTool}" is not supported or misspelled.

What it means

Thrown by JavaMicronautAbstractCodegen.processOpts when the buildTool additional property is present but not one of the Micronaut generator's supported values: 'gradle', 'maven', or 'all' (both build files). The switch on the raw string has no looser fallback, so any typo or unsupported tooling rejects generation before templates render. A sibling switch validates testTool as 'junit' or 'spock' the same way.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaMicronautAbstractCodegen.java:275

            this.wrapInHttpResponse = convertPropertyToBoolean(OPT_WRAP_IN_HTTP_RESPONSE);
        }
        writePropertyBack(OPT_WRAP_IN_HTTP_RESPONSE, wrapInHttpResponse);

        if (additionalProperties.containsKey(OPT_GENERATE_OPERATION_ONLY_FOR_FIRST_TAG)) {
            this.generateOperationOnlyForFirstTag = convertPropertyToBoolean(OPT_GENERATE_OPERATION_ONLY_FOR_FIRST_TAG);
        }
        writePropertyBack(OPT_GENERATE_OPERATION_ONLY_FOR_FIRST_TAG, generateOperationOnlyForFirstTag);

        // Get enum properties
        if (additionalProperties.containsKey(OPT_BUILD)) {
            switch ((String) additionalProperties.get(OPT_BUILD)) {
                case OPT_BUILD_GRADLE:
                case OPT_BUILD_MAVEN:
                case OPT_BUILD_ALL:
                    this.buildTool = (String) additionalProperties.get(OPT_BUILD);
                    break;
                default:
                    throw new RuntimeException("Build tool \"" + additionalProperties.get(OPT_BUILD) + "\" is not supported or misspelled.");
            }
        }
        additionalProperties.put(OPT_BUILD, buildTool);

        if (additionalProperties.containsKey(OPT_TEST)) {
            switch ((String) additionalProperties.get(OPT_TEST)) {
                case OPT_TEST_JUNIT:
                case OPT_TEST_SPOCK:
                    this.testTool = (String) additionalProperties.get(OPT_TEST);
                    break;
                default:
                    throw new RuntimeException("Test tool \"" + additionalProperties.get(OPT_TEST) + "\" is not supported or misspelled.");
            }
        }
        additionalProperties.put(OPT_TEST, testTool);
        if (testTool.equals(OPT_TEST_JUNIT)) {
            additionalProperties.put("isTestJunit", true);
        } else if (testTool.equals(OPT_TEST_SPOCK)) {

View on GitHub (pinned to fcec517be3)

Solutions

Use exactly one of: buildTool=gradle, buildTool=maven, or buildTool=all
Check the testTool value too — only junit and spock are accepted
For Kotlin-dsl Gradle files, generate with buildTool=gradle and rename/adjust the generated build script afterwards
Verify values against `openapi-generator-cli config-help -g java-micronaut-server` after generator upgrades

Example fix

# before
openapi-generator-cli generate -g java-micronaut-server -i api.yaml \
  --additional-properties buildTool=gradlew

# after
openapi-generator-cli generate -g java-micronaut-server -i api.yaml \
  --additional-properties buildTool=gradle

Defensive patterns

Strategy: validation

Validate before calling

Set<String> builds = Set.of("gradle", "maven", "all");
String buildTool = String.valueOf(opts.getOrDefault("buildTool", "gradle"));
if (!builds.contains(buildTool)) {
    throw new IllegalArgumentException("buildTool must be one of " + builds + ", got: " + buildTool);
}
Set<String> tests = Set.of("junit", "spock");
String testTool = String.valueOf(opts.getOrDefault("testTool", "junit"));
if (!tests.contains(testTool)) {
    throw new IllegalArgumentException("testTool must be one of " + tests + ", got: " + testTool);
}

Try / catch

try {
    generator.generate();
} catch (RuntimeException e) {
    if (e.getMessage() != null && (e.getMessage().contains("Build tool") || e.getMessage().contains("Test tool"))) {
        throw new ConfigException("Micronaut generator rejected buildTool/testTool: " + e.getMessage(), e);
    }
    throw e;
}

Prevention

Lowercase and whitelist buildTool/testTool values at config load time
Use the tool names (maven, gradle), not binary names (mvn, gradlew)
For Kotlin-dsl Gradle, generate with 'gradle' and post-process the script rather than inventing unsupported values

When it happens

Trigger: Passing --additional-properties buildTool=gradlew, buildTool=gradle-kotlin, buildTool=mvn, or empty string to -g java-micronaut* generators (client/server). Also triggered via Gradle plugin configOptions { buildTool = 'Gradle' } with wrong casing from Groovy configs, or stale config files using values removed in newer generator versions.

Common situations: Maven users type the mvn binary name instead of 'maven'. Kotlin-DSL Gradle users expect 'gradle-kotlin'/'kotlin' support that does not exist and must post-process the .gradle output. Case sensitivity bites when the value comes from a templated CI variable ('Gradle').

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/4d08247eddbde806. Report an issue: GitHub.