flowable/flowable-engine · error · FlowableIllegalArgumentException

Only 'binary' and 'serializable' are supported as variable t

Error message

Only 'binary' and 'serializable' are supported as variable type.

What it means

FlowableIllegalArgumentException thrown by setBinaryVariable when the optional 'variableType' form field is provided but is neither 'binary' nor 'serializable' (the two types CmmnRestResponseFactory supports for binary variables).

Source

Thrown at modules/flowable-cmmn-rest/src/main/java/org/flowable/cmmn/rest/service/api/runtime/caze/BaseVariableResource.java:348

                } else if ("name".equalsIgnoreCase(parameterName)) {
                    variableName = paramMap.get(parameterName)[0];

                } else if ("type".equalsIgnoreCase(parameterName)) {
                    variableType = paramMap.get(parameterName)[0];
                }
            }
        }

        try {

            // Validate input and set defaults
            if (variableName == null) {
                throw new FlowableIllegalArgumentException("No variable name was found in request body.");
            }

            if (variableType != null) {
                if (!CmmnRestResponseFactory.BYTE_ARRAY_VARIABLE_TYPE.equals(variableType) && !CmmnRestResponseFactory.SERIALIZABLE_VARIABLE_TYPE.equals(variableType)) {
                    throw new FlowableIllegalArgumentException("Only 'binary' and 'serializable' are supported as variable type.");
                }
            } else {
                variableType = CmmnRestResponseFactory.BYTE_ARRAY_VARIABLE_TYPE;
            }

            if (variableScope != null) {
                scope = RestVariable.getScopeFromString(variableScope);
            }

            if (variableType.equals(CmmnRestResponseFactory.BYTE_ARRAY_VARIABLE_TYPE)) {
                // Use raw bytes as variable value
                byte[] variableBytes = IOUtils.toByteArray(file.getInputStream());
                setVariable(instanceId, variableName, variableBytes, scope, isNew, async, variableInterceptor);

            } else if (isSerializableVariableAllowed) {
                // Try deserializing the object
                ObjectInputStream stream = new ObjectInputStream(file.getInputStream());
                Object value = stream.readObject();

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Set variableType=binary for raw bytes or variableType=serializable for Java-serialized objects.
2. Omit the variableType field entirely to default to 'binary'.
3. Use lowercase exact strings; any other type is rejected.

Example fix

// before
-F "variableName=doc" -F "variableType=string"
// after
-F "variableName=doc" -F "variableType=binary"   # or omit variableType

const ALLOWED = ['binary', 'serializable'];
if (variableType && !ALLOWED.includes(variableType)) {
  throw new Error(`variableType must be one of ${ALLOWED}, got '${variableType}'`);
}

function isBinaryVariableType(t) { return t == null || t === 'binary' || t === 'serializable'; }

try {
  await uploadBinaryVariable(id, formData);
} catch (e) {
  if (/Only 'binary' and 'serializable'/.test(e.message)) throw new Error('Use variableType=binary or serializable, or omit it');
  throw e;
}

When it happens

Trigger: Multipart binary variable upload with variableType=form, string, json, or any other unsupported string.

Common situations: Copy-pasting variableType values from the general (JSON) variable API, which supports many types; case-sensitivity mistakes ('Binary'); clients guessing the type field values.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Variable '${restVariable.getName()}' has unsupported type: '
• Unsupported variable query operation: ${friendlyName}
• Invalid variable scope: '${scope}'
• Request didn't contain a list of variables to create.
• Variable name is required

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/cd7507c22a6d7b29. Report an issue: GitHub.