flowable/flowable-engine · error · FlowableIllegalArgumentException

Value of type ${value.getClass()} is not supported as multi

Error message

Value of type ${value.getClass()} is not supported as multi part content

What it means

When building multipart bodies, setRequestEntity only supports String values (text parts, optionally with a mime type) — null values are skipped. Any other non-null object type is rejected with FlowableIllegalArgumentException naming the offending Java type, because there is no defined mapping to a MIME part.

Source

Thrown at modules/flowable-http-common/src/main/java/org/flowable/http/common/impl/apache/ApacheHttpComponentsFlowableHttpClient.java:274

                MultipartEntityBuilder entityBuilder = MultipartEntityBuilder.create();
                entityBuilder.setMode(multipartMode);
                for (MultiValuePart part : requestInfo.getMultiValueParts()) {
                    String name = part.getName();
                    Object value = part.getBody();
                    if (value instanceof byte[]) {
                        if (StringUtils.isNotBlank(part.getMimeType())) {
                            entityBuilder.addBinaryBody(name, (byte[]) value, ContentType.create(part.getMimeType()), part.getFilename());
                        } else {
                            entityBuilder.addBinaryBody(name, (byte[]) value, ContentType.DEFAULT_BINARY, part.getFilename());
                        }
                    } else if (value instanceof String) {
                        if (StringUtils.isNotBlank(part.getMimeType())) {
                            entityBuilder.addTextBody(name, (String) value, ContentType.create(part.getMimeType()));
                        } else {
                            entityBuilder.addTextBody(name, (String) value);
                        }
                    } else if (value != null) {
                        throw new FlowableIllegalArgumentException("Value of type " + value.getClass() + " is not supported as multi part content");
                    }
                }
                requestBase.setEntity(entityBuilder.build());
            } else {
                throw new FlowableException("org.apache.http.entity.mime.MultipartEntityBuilder is not present on the classpath."
                        + " Multi value parts cannot be used."
                        + " If you want to use, please make sure that the org.apache.httpcomponents:httpmime dependency is available");
            }

        } else if (requestInfo.getFormParameters() != null) {
            Map<String, List<String>> formParameters = requestInfo.getFormParameters();
            List<BasicNameValuePair> parameters = new ArrayList<>(formParameters.size());
            for (Map.Entry<String, List<String>> entry : formParameters.entrySet()) {
                String name = entry.getKey();
                for (String value : entry.getValue()) {
                    parameters.add(new BasicNameValuePair(name, value));
                }
            }

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Convert the value to String before the task (String.valueOf or serialization in a script/listener)
2. For binary content, check which part types the configured client supports and use the appropriate field type/format
3. Fix the variable producer so the bound variable is a String
4. Split the request: send non-string data as JSON body instead of multipart

Example fix

// before
execution.setVariable("amount", 42); // bound to multipart field
// after
execution.setVariable("amount", String.valueOf(42));

Object v = execution.getVariable("partValue");
if (v != null && !(v instanceof String)) {
    execution.setVariable("partValue", String.valueOf(v));
}

boolean isMultipartCompatible(Object v) { return v == null || v instanceof String; }

try {
    client.prepareRequest(requestInfo);
} catch (FlowableIllegalArgumentException e) {
    if (e.getMessage() != null && e.getMessage().contains("not supported as multi part content")) {
        // stringify the offending variable and retry once
    } else { throw e; }
}

When it happens

Trigger: A multipart field (fieldValue / part value) in the HTTP task resolves to a non-String object — e.g. an Integer, byte[], Map, or POJO process variable — while the request has parts configured.

Common situations: Binding a numeric or binary variable from a previous service task into a multipart field; JSON-deserialized objects used directly as part values; forgetting to convert a file's bytes to a supported representation.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Multipart request is required
• Value of type ${value.getClass()} is not supported as multi
• Invalid usage of async_activate job handler, variable scope
• Invalid usage of ${TYPE} job handler, variable scope is of t
• Delegate expression ${expression} did not resolve to an impl

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/e35121e0511eaa13. Report an issue: GitHub.