flowable/flowable-engine · error · FlowableIllegalArgumentException

Only string variable values are supported using like, but wa

Error message

Only string variable values are supported using like, but was: 

What it means

The LIKE variable operator on historic task instance queries only accepts String values; Flowable throws FlowableIllegalArgumentException with the value's class name when the supplied value is not a String.

Source

Thrown at modules/flowable-rest/src/main/java/org/flowable/rest/service/api/history/HistoricTaskInstanceBaseResource.java:407

                break;

            case GREATER_THAN_OR_EQUALS:
                taskInstanceQuery.taskVariableValueGreaterThanOrEqual(variable.getName(), actualValue);
                break;

            case LESS_THAN:
                taskInstanceQuery.taskVariableValueLessThan(variable.getName(), actualValue);
                break;

            case LESS_THAN_OR_EQUALS:
                taskInstanceQuery.taskVariableValueLessThanOrEqual(variable.getName(), actualValue);
                break;

            case LIKE:
                if (actualValue instanceof String) {
                    taskInstanceQuery.taskVariableValueLike(variable.getName(), (String) actualValue);
                } else {
                    throw new FlowableIllegalArgumentException("Only string variable values are supported using like, but was: " + actualValue.getClass().getName());
                }
                break;

            case LIKE_IGNORE_CASE:
                if (actualValue instanceof String) {
                    taskInstanceQuery.taskVariableValueLikeIgnoreCase(variable.getName(), (String) actualValue);
                } else {
                    throw new FlowableIllegalArgumentException("Only string variable values are supported using like, but was: " + actualValue.getClass().getName());
                }
                break;

            case EXISTS:
                taskInstanceQuery.taskVariableExists(variable.getName());
                break;

            case NOT_EXISTS:
                taskInstanceQuery.taskVariableNotExists(variable.getName());
                break;

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Quote the value in JSON: {"operation":"like","value":"%foo%"}
2. Use 'equals' with an exact value for non-string types
3. Convert the underlying variable to String if partial matching is required

Example fix

// before
{"name":"count","operation":"like","value":%5%}
// after
{"name":"description","operation":"like","value":"%urgent%"}

if (!(variable.getValue() instanceof String))
    throw new IllegalArgumentException("like requires a String value");

boolean isStringFilter(QueryVariable v) { return v.getValue() instanceof String; }

try { queryTaskVariables(vars); }
catch (FlowableIllegalArgumentException e) { /* fall back to equals */ }

When it happens

Trigger: POST /query/historic-tasks with a taskVariables entry using operation 'like' whose value is a non-string (e.g. unquoted number or boolean).

Common situations: Wildcard search attempted on a numeric variable; JSON value not quoted; template that formats numbers into the like filter without string conversion.

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

• Only string variable values are supported when ignoring casi
• Only string variable values are supported when ignoring casi
• Only string variable values are supported when ignoring casi
• Variable operation is missing for variable: " + variable.get
• Variable value is missing for variable: " + variable.getName

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/9253086cfc98cf7f. Report an issue: GitHub.