flowable/flowable-engine · error · FlowableContentNotSupportedException

The provided body contains a serialized object for which…

Error message

The provided body contains a serialized object for which the class was not found:

What it means

FlowableContentNotSupportedException thrown when deserializing the uploaded object fails with ClassNotFoundException in setBinaryVariable. The request body contained a Java-serialized object whose class is not on the Flowable server's classpath, so the server cannot reconstruct it. The missing class name is appended to the message.

Solutions

  1. Add the missing class (named in the message) to the Flowable server classpath
  2. Align package/class names between client and server deployments
  3. Prefer JSON variables over Java serialization for portability
  4. Include serialVersionUID-compatible class versions on both sides

Example fix

// before: uploading instance of com.myapp.CustomDto not present on server
// after: add myapp-dto jar to server libs, or send JSON:
PUT /cmmn-runtime/tasks/{id}/variables  {"name":"v","type":"string","value":"..."}
Defensive patterns

Strategy: try-catch

Validate before calling

const isSerializableClass = (cls) => /* verify class name matches a class deployed on the server */ deployedClassNames.has(cls.name);

Try / catch

try { await uploadSerializable(obj) } catch (e) { if (e.message.includes('class was not found')) deployMissingClass(e.cause) ?? useJsonInstead(obj); }

Prevention

When it happens

Trigger: Uploading type='serializable' content whose serialized stream references a class absent from the server's classpath — the ClassNotFoundException message names the missing class.

Common situations: Deploying a custom class version that was later renamed/refactored; server missing the client application's domain classes; different package names between client and server builds; running on Flowable server without the app's dependency jars.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/d042851fdc14d6cf. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-cmmn-rest/src/main/java/org/flowable/cmmn/rest/service/api/runtime/task/TaskVariableBaseResource.java:199

                setVariable(task, variableName, variableBytes, scope, isNew);

            } else if (isSerializableVariableAllowed) {
                // Try deserializing the object
                ObjectInputStream stream = new ObjectInputStream(file.getInputStream());
                Object value = stream.readObject();
                setVariable(task, variableName, value, scope, isNew);
                stream.close();

            } else {
                throw new FlowableContentNotSupportedException("Serialized objects are not allowed");
            }

            return getVariableFromRequestWithoutAccessCheck(task, variableName, scope, false);

        } catch (IOException ioe) {
            throw new FlowableIllegalArgumentException("Error getting binary variable", ioe);
        } catch (ClassNotFoundException ioe) {
            throw new FlowableContentNotSupportedException("The provided body contains a serialized object for which the class was not found: " + ioe.getMessage());
        }

    }

    protected RestVariable setSimpleVariable(RestVariable restVariable, Task task, boolean isNew) {
        if (restVariable.getName() == null) {
            throw new FlowableIllegalArgumentException("Variable name is required");
        }

        // Figure out scope, revert to local is omitted
        RestVariableScope scope = restVariable.getVariableScope();
        if (scope == null) {
            scope = RestVariableScope.LOCAL;
        }

        Object actualVariableValue = restResponseFactory.getVariableValue(restVariable);
        setVariable(task, restVariable.getName(), actualVariableValue, scope, isNew);

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