apache/pulsar · error · IllegalArgumentException

com.google.protobuf.Message is not assignable from ${pojo.ge

Error message

com.google.protobuf.Message is not assignable from ${pojo.getName()}

What it means

ProtobufNativeSchema.of(SchemaDefinition) requires the schema's POJO to implement com.google.protobuf.Message. Otherwise it throws IllegalArgumentException stating Message is not assignable from the pojo's class name.

Source

Thrown at pulsar-client/src/main/java/org/apache/pulsar/client/impl/schema/ProtobufNativeSchema.java:123

    }

    public static <T extends Message> ProtobufNativeSchema<T> of(Class<T> pojo) {
        return of(pojo, new HashMap<>());
    }

    @SuppressWarnings("unchecked")
    public static <T> ProtobufNativeSchema ofGenericClass(Class<T> pojo, Map<String, String> properties) {
        SchemaDefinition<T> schemaDefinition = SchemaDefinition.<T>builder().withPojo(pojo)
                .withProperties(properties).build();
        return ProtobufNativeSchema.of(schemaDefinition);
    }

    @SuppressWarnings("unchecked")
    public static <T> ProtobufNativeSchema of(SchemaDefinition<T> schemaDefinition) {
        Class<T> pojo = schemaDefinition.getPojo();

        if (!Message.class.isAssignableFrom(pojo)) {
            throw new IllegalArgumentException(Message.class.getName()
                    + " is not assignable from " + pojo.getName());
        }
        Descriptors.Descriptor descriptor = createProtobufNativeSchema(schemaDefinition.getPojo());

        SchemaInfo schemaInfo = SchemaInfoImpl.builder()
                .schema(ProtobufNativeSchemaUtils.serialize(descriptor))
                .type(SchemaType.PROTOBUF_NATIVE)
                .name("")
                .properties(schemaDefinition.getProperties())
                .build();
        try {
            return new ProtobufNativeSchema(schemaInfo,
                    (Message) pojo.getMethod("getDefaultInstance").invoke(null));
        } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
            throw new IllegalArgumentException(e);
        }
    }

View on GitHub (pinned to 820761864e)

Solutions

Generate the message class with protoc / protobuf-maven-plugin and pass that generated class to SchemaDefinition.of(...)
Use Schema.AVRO(...)/JSONSchema for non-protobuf POJOs
Verify the class actually implements com.google.protobuf.Message (check generated sources and protobuf dependency version)

Example fix

// before
SchemaDefinition<Object> def = SchemaDefinition.<Object>builder().withPojo(PlainPojo.class).build();
ProtobufNativeSchema.of(def); // throws
// after
SchemaDefinition<GeneratedMsg> def = SchemaDefinition.<GeneratedMsg>builder().withPojo(GeneratedMsg.class).build();
ProtobufNativeSchema.of(def);

Defensive patterns

Strategy: type-guard

Validate before calling

if (!com.google.protobuf.Message.class.isAssignableFrom(pojo)) { throw new IllegalArgumentException(pojo + " must implement Message"); }

Type guard

boolean isProtobufMessage(Class<?> c) { return com.google.protobuf.Message.class.isAssignableFrom(c); }

Try / catch

try { ProtobufNativeSchema.of(def); } catch (IllegalArgumentException e) { /* fall back to AVRO/JSON schema or fix pojo */ }

Prevention

Ensure classes passed to SchemaDefinition.of are protoc-generated
Run protobuf-maven-plugin/protoc in the build
Check the instanceof-Msg contract before choosing ProtobufNativeSchema

When it happens

Trigger: Calling ProtobufNativeSchema.of(SchemaDefinition.of(SomePojo.class)) where SomePojo is not a generated protobuf message class (a plain Java bean, an Avro POJO, or a hand-written class).

Common situations: Using ProtobufNativeSchema with a non-protobuf class by mistake; confusing ProtobufSchema/ProtobufNativeSchema requirements; a proto file compiled without protoc so no Message subclass was generated.

Related errors

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/5138c801ced24bd3. Report an issue: GitHub.