What causes "Exception while executing {} : {}" in flowable/flowable-engine?

Read the logged root-cause message and fix the script

Exception while executing

Error message

Exception while executing {} : {}

What it means

Logged by ScriptTaskActivityBehavior when script execution throws an ActivitiException. The script task's activity id and message are logged, then the root cause is inspected: if it is a BpmnError it is propagated to error handling, otherwise the failure continues as a normal script failure.

Solutions

Read the logged root-cause message and fix the script
Throw BpmnError from the script if error-boundary handling was intended
Verify the script engine (e.g. groovy) dependency is present and the script compiles

Example fix

// before (script)
throw new RuntimeException("bad input");
// after (intended error handling)
throw new org.activiti.engine.delegate.BpmnError("BAD_INPUT");

Defensive patterns

Strategy: type-guard

Validate before calling

// validate script input variables exist before the script task runs
if (execution.getVariable("input") == null) throw new BpmnError("MISSING_INPUT");

Type guard

if (ExceptionUtils.getRootCause(e) instanceof BpmnError) { /* routed to boundary error */ }

Try / catch

try { scriptEngine.eval(script, bindings); } catch (ScriptException e) { throw new ActivitiException("script failed", e); }

Prevention

Unit-test scripts with the same engine used at runtime
Include the script engine dependency (e.g. groovy) in the deployment artifact
Throw BpmnError deliberately when boundary error handling is intended

When it happens

Trigger: A BPMN script task whose script throws/compiles-fails (e.g. groovy/javascript engine errors, missing bindings) wrapped in an ActivitiException.

Common situations: Script syntax errors, missing script engine dependency on the classpath, scripts referencing undefined variables, intended BpmnError signaling from scripts.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/a8a4ac522ee19925. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/bpmn/behavior/ScriptTaskActivityBehavior.java:86

            if (taskElementProperties != null && taskElementProperties.has(DynamicBpmnConstants.SCRIPT_TASK_SCRIPT)) {
                String overrideScript = taskElementProperties.get(DynamicBpmnConstants.SCRIPT_TASK_SCRIPT).asString();
                if (StringUtils.isNotEmpty(overrideScript) && !overrideScript.equals(script)) {
                    script = overrideScript;
                }
            }
        }

        boolean noErrors = true;
        try {
            Object result = scriptingEngines.evaluate(script, language, execution, storeScriptVariables);

            if (resultVariable != null) {
                execution.setVariable(resultVariable, result);
            }

        } catch (ActivitiException e) {

            LOGGER.warn("Exception while executing {} : {}", activityExecution.getActivity().getId(), e.getMessage());

            noErrors = false;
            Throwable rootCause = ExceptionUtils.getRootCause(e);
            if (rootCause instanceof BpmnError) {
                ErrorPropagation.propagateError((BpmnError) rootCause, activityExecution);
            } else {
                throw e;
            }
        }
        if (noErrors) {
            leave(activityExecution);
        }
    }

}

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