apache/pulsar · error · IllegalArgumentException

Only one of schemaType or serdeClassName should be set in in

Error message

Only one of schemaType or serdeClassName should be set in inputSpec

What it means

Each input spec must set at most one of schemaType and serdeClassName, since they are competing ways to declare the input deserializer. doJavaChecks throws IllegalArgumentException when both are non-empty for the same topic.

Source

Thrown at pulsar-functions/utils/src/main/java/org/apache/pulsar/functions/utils/FunctionConfigUtils.java:694

                try {
                    consumerConfig = OBJECT_MAPPER.readValue(conf, ConsumerConfig.class);
                } catch (JsonProcessingException e) {
                    throw new IllegalArgumentException(
                            String.format("Topic %s has an incorrect schema Info", topicName));
                }
                ValidatorUtils.validateSchema(consumerConfig.getSchemaType(), typeArgs[0],
                        validatableFunctionPackage.getTypePool(), true);
            });
        }

        // Check if the Input serialization/deserialization class exists in jar or already loaded and that it
        // implements Schema or SerDe classes

        if (functionConfig.getInputSpecs() != null) {
            functionConfig.getInputSpecs().forEach((topicName, conf) -> {
                // Need to make sure that one and only one of schema/serde is set
                if (!isEmpty(conf.getSchemaType()) && !isEmpty(conf.getSerdeClassName())) {
                    throw new IllegalArgumentException(
                        "Only one of schemaType or serdeClassName should be set in inputSpec");
                }
                if (!isEmpty(conf.getSerdeClassName())) {
                    ValidatorUtils.validateSerde(conf.getSerdeClassName(), typeArgs[0],
                            validatableFunctionPackage.getTypePool(), true);
                }
                if (!isEmpty(conf.getSchemaType())) {
                    ValidatorUtils.validateSchema(conf.getSchemaType(), typeArgs[0],
                            validatableFunctionPackage.getTypePool(), true);
                }
                if (conf.getCryptoConfig() != null) {
                    ValidatorUtils.validateCryptoKeyReader(conf.getCryptoConfig(),
                            validatableFunctionPackage.getTypePool(), false);
                }
                if (conf.getMessagePayloadProcessorConfig() != null) {
                    ValidatorUtils.validateMessagePayloadProcessor(conf.getMessagePayloadProcessorConfig(),
                            validatableFunctionPackage.getTypePool());
                }

View on GitHub (pinned to 820761864e)

Solutions

1. Remove serdeClassName and keep schemaType (recommended)
2. Or remove schemaType and keep serdeClassName for legacy SerDe usage
3. Audit inputSpecs programmatically before submission to ensure exclusivity

Example fix

// before
inputSpec.setSchemaType("avro");
inputSpec.setSerdeClassName("com.example.MySerde");
// after
inputSpec.setSchemaType("avro");

config.getInputSpecs().forEach((topic, spec) -> { if (notBlank(spec.getSchemaType()) && notBlank(spec.getSerdeClassName())) throw new IllegalArgumentException("topic " + topic + " sets both schemaType and serdeClassName"); });

boolean exclusiveSerializer(InputSpec s) { return isBlank(s.getSchemaType()) || isBlank(s.getSerdeClassName()); }

try { ... } catch (IllegalArgumentException e) { if (e.getMessage().contains("Only one of schemaType or serdeClassName")) { log.error("Clear one serializer field in inputSpecs"); } }

When it happens

Trigger: FunctionConfig inputSpecs containing an InputSpec with both setSchemaType(...) and setSerdeClassName(...) populated for the same topic, typically from merged/legacy configs.

Common situations: Upgrading from old SerDe-based configs to schema-based configs leaving both fields set; copy-pasted config templates combining both styles.

Related errors

• Only one of outputSchemaType or outputSerdeClassName should
• When Guarantees == ATMOST_ONCE, autoAck must be equal to tru
• Function class name is not provided.
• Topic %s has an incorrect schema Info
• Function tenant cannot be null

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/916fbe5ad753f6c5. Report an issue: GitHub.