flowable/flowable-engine · error · FlowableContentNotSupportedException

The provided body contains a serialized object for which the

Error message

The provided body contains a serialized object for which the class was not found: " + ioe.getMessage()

What it means

FlowableContentNotSupportedException thrown when deserializing a variable body whose Java class is not on the REST server's classpath. The REST API deserializes serialized Java objects sent as binary variables; if the object's class cannot be loaded, the request is rejected. This protects against silently accepting an unusable variable value.

Source

Thrown at modules/flowable-rest/src/main/java/org/flowable/rest/service/api/runtime/process/BaseExecutionVariableResource.java:187

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

            RestVariable variable = null;
            
            if (!async) {
                variable = getVariableFromRequestWithoutAccessCheck(execution, variableName, scope, false);
                
                // We are setting the scope because the fetched variable does not have it
                variable.setVariableScope(scope);
            }
            
            return variable;

        } catch (IOException ioe) {
            throw new FlowableIllegalArgumentException("Could not process multipart content", 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, Execution execution, boolean isNew, boolean async) {
        if (restVariable.getName() == null) {
            throw new FlowableIllegalArgumentException("Variable name is required");
        }

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

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

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Ensure the serialized class (and its package) is present on the server's classpath, e.g. add the client's domain jar to flowable-rest's WEB-INF/lib
2. Prefer sending JSON or primitive values instead of raw Java-serialized objects
3. If the class was refactored, re-serialize the variable with the new class name or use a serialization filter/Compatibility mode
4. Check that client and server share the same version of the library defining the class

Example fix

// before
classpath: flowable-rest.war (no domain classes)
ObjectOutputStream oos = new ObjectOutputStream(out); oos.writeObject(myCustomDto);
// after
// add domain-classes.jar to flowable-rest/WEB-INF/lib so ClassNotFoundException disappears

Class<?> c = null;
try { c = Class.forName(myDto.getClass().getName(), false, Thread.currentThread().getContextClassLoader()); } catch (ClassNotFoundException ignored) {}
if (c == null) throw new IllegalStateException("Class " + myDto.getClass().getName() + " must be on the flowable-rest server classpath");

static boolean isSerializableSafe(Object o) { return o instanceof String || o instanceof Number || o instanceof Boolean || o instanceof byte[]; }

try {
    restClient.setBinaryVariable(executionId, name, body);
} catch (HttpServerErrorException | HttpClientErrorException e) {
    if (e.getResponseBodyAsString().contains("class was not found")) { /* fall back to JSON transport */ }
}

When it happens

Trigger: POST/PUT of a binary variable with a Java-serialized object (Content-Type application/x-java-serialized-object) whose class was removed from the server or never deployed there.

Common situations: Client serializes a custom POJO that exists on the client but not in the flowable-rest webapp's classpath; server upgraded and the class was renamed/moved; different library versions on client and server.

Related errors

• Unexpected exception getting variable data
• Error getting variable ${variable.getName()}
• The provided body contains a serialized object for which the
• Error getting variable ${variableName}
• Error writing form model response

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/6f4436db4aaa0d68. Report an issue: GitHub.