flowable/flowable-engine · error · ActivitiException

Couldn't deserialize object in variable ''

Error message

Couldn't deserialize object in variable ''

What it means

Thrown by SerializableType.deserialize when reading a stored, Java-serialized variable back with ObjectInputStream fails. The variable name is included in the message and the underlying exception (ClassNotFoundException, InvalidClassException, IOException, StreamCorruptedException) is the cause.

Solutions

  1. Restore the class (or a compatible version with matching serialVersionUID) to the classpath.
  2. Add a fixed serialVersionUID to variable classes and keep it stable across releases.
  3. Inspect the cause: ClassNotFoundException -> deployment/classpath issue; InvalidClassException -> schema change; StreamCorruptedException -> data corruption.
  4. Migrate legacy variables to a stable format (e.g. JSON) or re-create them.
  5. Catch ActivitiException around variable reads and fall back to re-initializing the variable.

Example fix

// before
public class OrderData { /* no serialVersionUID, fields changed */ }
// after
public class OrderData implements Serializable {
    private static final long serialVersionUID = 1L;
}
Defensive patterns

Strategy: try-catch

Try / catch

try { Object v = taskService.getVariable(taskId, "order"); } catch (ActivitiException e) {
  log.error("Deserializing variable 'order' failed: {}", e.getCause(), e);
  // fallback: re-initialize or migrate the variable
}

Prevention

When it happens

Trigger: Reading a serializable variable whose class is not on the classpath (ClassNotFoundException), whose serialVersionUID changed (InvalidClassException), or whose stored bytes are corrupt/migrated between formats.

Common situations: Upgrading the application and changing variable class definitions without serialVersionUID; moving variables between databases/environments; removing old DTO classes from the classpath; switching JVMs with incompatible serialization.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/99e06cb00072806e. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/variable/SerializableType.java:120

            oos = createObjectOutputStream(baos);
            oos.writeObject(value);
        } catch (Exception e) {
            throw new ActivitiException("Couldn't serialize value '" + value + "' in variable '" + valueFields.getName() + "'", e);
        } finally {
            IoUtil.closeSilently(oos);
        }
        return baos.toByteArray();
    }

    public Object deserialize(byte[] bytes, ValueFields valueFields) {
        ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
        try {
            ObjectInputStream ois = createObjectInputStream(bais);
            Object deserializedObject = ois.readObject();

            return deserializedObject;
        } catch (Exception e) {
            throw new ActivitiException("Couldn't deserialize object in variable '" + valueFields.getName() + "'", e);
        } finally {
            IoUtil.closeSilently(bais);
        }
    }

    @Override
    public boolean isAbleToStore(Object value) {
        // TODO don't we need null support here?
        return value instanceof Serializable;
    }

    protected ObjectInputStream createObjectInputStream(InputStream is) throws IOException {
        return new ObjectInputStream(is) {
            @Override
            protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, ClassNotFoundException {
                return ReflectUtil.loadClass(desc.getName());
            }
        };

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