flowable/flowable-engine · error · XMLException

Error writing CMMN XML

Error message

Error writing CMMN XML

What it means

convertToXML wraps any exception raised while serializing a CmmnModel to XML bytes (including StAX writing and schema validation failures) into XMLException("Error writing CMMN XML"). It indicates the model could not be serialized, often because it is incomplete or violates the CMMN schema.

Source

Thrown at modules/flowable-cmmn-converter/src/main/java/org/flowable/cmmn/converter/CmmnXmlConverter.java:344

            }

            CmmnDIExport.writeCmmnDI(model, xtw);

            // end definitions root element
            xtw.writeEndElement();
            xtw.writeEndDocument();

            xtw.flush();

            outputStream.close();

            xtw.close();

            return outputStream.toByteArray();

        } catch (Exception e) {
            LOGGER.error("Error writing CMMN XML", e);
            throw new XMLException("Error writing CMMN XML", e);
        }
    }

    protected void processCmmnElements(ConversionHelper conversionHelper) {
        CmmnModel cmmnModel = conversionHelper.getCmmnModel();
        for (Case caze : cmmnModel.getCases()) {
            processPlanFragment(cmmnModel, caze.getPlanModel());
        }

        // CMMN doesn't mandate ids on many elements ... adding generated ids
        // to those elements as this makes the logic much easier
        ensureIds(conversionHelper.getPlanFragments(), "planFragment_");
        ensureIds(conversionHelper.getStages(), "stage_");
        ensureIds(conversionHelper.getEntryCriteria(), "entryCriterion_");
        ensureIds(conversionHelper.getExitCriteria(), "exitCriterion_");
        ensureIds(conversionHelper.getSentries(), "sentry_");
        ensureIds(conversionHelper.getSentryOnParts(), "onPart_");
        ensureIds(conversionHelper.getSentryIfParts(), "ifPart_");

View on GitHub (pinned to d6d39ce1c6)

Solutions

  1. Read the chained cause to see which element/attribute failed serialization or validation
  2. Validate the CmmnModel programmatically before conversion (required ids/refs non-null, definitionRef/sentryRef resolvable)
  3. Use convertToCmmnModel round-tripping to sanity-check models built by code
  4. Pass a valid charset name as the encoding argument

Example fix

// before
CmmnModel model = new CmmnModel(); // no cases/ids set
converter.convertToXML(model);
// after
CmmnModel model = buildCompleteModel(); // set ids, cases, plan items
byte[] xml = converter.convertToXML(model); // validates against XSD
Defensive patterns

Strategy: try-catch

Validate before calling

if (model.getCases() == null || model.getCases().isEmpty())
    throw new IllegalStateException("CmmnModel has no cases; nothing valid to serialize");

Try / catch

try {
    byte[] xml = converter.convertToXML(model);
} catch (XMLException e) {
    log.error("CMMN serialization failed", e.getCause());
    throw new DeploymentException("Model cannot be written as CMMN XML", e);
}

Prevention

When it happens

Trigger: Calling CmmnXmlConverter.convertToXML(model) or convertToXML(model, encoding) with a model containing null/invalid required elements, an unsupported encoding name, or content failing XSD validation during output.

Common situations: Programmatically constructed CmmnModel missing required fields (e.g. null case/stage ids), models imported from incompatible sources, or deploying a model that was never validated.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/54b5fb93ffcdecf3. Report an issue: GitHub.