apache/beam · error · RuntimeException

Unable to generate a creator for class {} with schema {}

Error message

Unable to generate a creator for class {} with schema {}

What it means

JavaBeanUtils.createConstructorCreator generates a SchemaUserTypeCreator that invokes a Java bean's constructor to build rows from a Beam Schema. If instantiating the generated creator class fails via reflection (InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException), this RuntimeException naming the class and schema is thrown.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/JavaBeanUtils.java:366

              .subclass(SchemaUserTypeCreator.class)
              .method(ElementMatchers.named("create"))
              .intercept(
                  new ConstructorCreateInstruction(
                      types, clazz, constructor, typeConversionsFactory));
      return builder
          .visit(new AsmVisitorWrapper.ForDeclaredMethods().writerFlags(ClassWriter.COMPUTE_FRAMES))
          .make()
          .load(
              ReflectHelpers.findClassLoader(clazz.getClassLoader()),
              getClassLoadingStrategy(clazz))
          .getLoaded()
          .getDeclaredConstructor()
          .newInstance();
    } catch (InstantiationException
        | IllegalAccessException
        | NoSuchMethodException
        | InvocationTargetException e) {
      throw new RuntimeException(
          "Unable to generate a creator for class " + clazz + " with schema " + schema);
    }
  }

  public static SchemaUserTypeCreator getStaticCreator(
      TypeDescriptor<?> typeDescriptor,
      Method creator,
      Schema schema,
      FieldValueTypeSupplier fieldValueTypeSupplier,
      TypeConversionsFactory typeConversionsFactory) {
    return CACHED_CREATORS.computeIfAbsent(
        TypeDescriptorWithSchema.create(typeDescriptor, schema),
        c -> {
          List<FieldValueTypeInformation> types =
              fieldValueTypeSupplier.get(typeDescriptor, schema);
          return createStaticCreator(
              typeDescriptor.getRawType(), creator, schema, types, typeConversionsFactory);
        });

View on GitHub (pinned to 12126d8942)

Solutions

Add a public no-arg constructor to the target class and make it concrete/public
Verify the constructor parameters match the schema fields (types and order)
Catch and inspect the cause exception to see which reflective step failed
If the class cannot have a no-arg constructor, provide a static creator method instead (getStaticCreator path)

Example fix

// before
public class Row { public Row(String name) { ... } }
// after
public class Row { public Row() {} public Row(String name) { ... } }

Defensive patterns

Strategy: validation

Validate before calling

static void checkCreatorTarget(Class<?> c) {
  if (java.lang.reflect.Modifier.isAbstract(c.getModifiers()))
    throw new IllegalArgumentException(c + " is abstract");
  try { c.getDeclaredConstructor(); }
  catch (NoSuchMethodException e) { throw new IllegalArgumentException("No no-arg constructor on " + c, e); }
}

Type guard

static boolean canBeSchemaRow(Class<?> c) {
  return java.lang.reflect.Modifier.isPublic(c.getModifiers())
      && !c.isInterface()
      && !java.lang.reflect.Modifier.isAbstract(c.getModifiers());
}

Try / catch

try {
  creator = JavaBeanUtils.getConstructorCreator(MyBean.class, schema, options);
} catch (RuntimeException e) {
  throw new IllegalStateException("Creator generation failed for " + MyBean.class + " with schema " + schema, e);
}

Prevention

Provide a public no-arg constructor on all schema row classes
Keep constructor parameter types aligned with schema field types
Prefer simple POJOs; avoid constructors with side effects that can throw
If no-arg ctor is impossible, expose a static factory creator instead

When it happens

Trigger: Calling JavaBeanUtils.getConstructorCreator/createConstructorCreator for a class whose constructor-based creator cannot be instantiated: the target class lacks an accessible no-arg constructor, is abstract, or constructor invocation throws at runtime.

Common situations: Using a bean without a public no-arg constructor as a schema type (e.g. with Schema.create/avro-like row encoding); constructor performing validation that throws on first invocation; class visibility mismatch across packages.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/dde601e68a7ba268. Report an issue: GitHub.