apache/beam · error · RuntimeException

Failed to instantiate object

Error message

Failed to instantiate object 

What it means

SetterBasedCreatorFactory.create builds schema-conformant objects by calling the no-arg constructor and then applying setters. If the target class has no accessible no-arg constructor (or the constructor throws), it wraps the reflective failure in a RuntimeException 'Failed to instantiate object'.

Solutions

1. Add a public no-arg constructor to the target class
2. Use a class with factory-method-based schema creation (@SchemaCreate) instead of setter-based instantiation
3. Make the class static/top-level so no enclosing instance is required
4. Inspect the wrapped cause (NoSuchMethodException/InstantiationException etc.) to identify the exact reflective failure

Example fix

// before
class MyClass { private final String a; MyClass(String a) { this.a = a; } }
// after
class MyClass { private String a; public MyClass() {} public String getA() { return a; } public void setA(String a) { this.a = a; } }

Class<?> c = typeDescriptor.getRawType();
if (c.isInterface() || java.lang.reflect.Modifier.isAbstract(c.getModifiers())) throw new IllegalArgumentException(c + " not instantiable");
try { c.getDeclaredConstructor(); } catch (NoSuchMethodException e) { throw new IllegalArgumentException(c + " lacks no-arg constructor"); }

boolean isInstantiable(Class<?> c) { try { c.getDeclaredConstructor(); return !c.isInterface() && !java.lang.reflect.Modifier.isAbstract(c.getModifiers()); } catch (NoSuchMethodException e) { return false; } }

try { return schemaCreator.create(params); } catch (RuntimeException e) { throw new IllegalStateException("Cannot instantiate " + targetType + ": add no-arg ctor or @SchemaCreate", e); }

When it happens

Trigger: Using schema-based conversion (e.g. SchemaCoder, DoFn schema transforms, fromRow/create) on a Java class without a public no-arg constructor, an abstract/interface type, or a constructor that throws (e.g. static init or constructor-side validation).

Common situations: Immutable classes with only builder/all-args constructors; inner non-static classes needing an enclosing instance; Kotlin/data classes without a no-arg ctor; missing public modifier on the constructor.

Related errors

• Can not call prepareRun
• A method marked with SchemaCreate in class
• AutoValue builder class
• Cannot create UDF from method: method
• Cannot determine context class

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/61264d3b2df82bdf. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SetterBasedCreatorFactory.java:51

  public SetterBasedCreatorFactory(Factory<List<FieldValueSetter>> setterFactory) {
    this.setterFactory = new CachingFactory<>(setterFactory);
  }

  @Override
  public SchemaUserTypeCreator create(TypeDescriptor<?> typeDescriptor, Schema schema) {
    List<FieldValueSetter> setters = setterFactory.create(typeDescriptor, schema);
    return new SchemaUserTypeCreator() {
      @Override
      public Object create(Object... params) {
        Object object;
        try {
          object = typeDescriptor.getRawType().getDeclaredConstructor().newInstance();
        } catch (NoSuchMethodException
            | IllegalAccessException
            | InvocationTargetException
            | InstantiationException e) {
          throw new RuntimeException("Failed to instantiate object ", e);
        }
        for (int i = 0; i < params.length; ++i) {
          FieldValueSetter setter = setters.get(i);
          setter.set(object, params[i]);
        }
        return object;
      }
    };
  }
}

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