flowable/flowable-engine · error · FlowableIllegalArgumentException

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

Error message

Only string variable values are supported for like, but was: " + actualValue.getClass().getName()

What it means

The LIKE variable query operation performs SQL-style pattern matching, which only makes sense for String variables. If the resolved value is not a String, addVariables throws FlowableIllegalArgumentException including the actual value's class name.

Source

Thrown at modules/flowable-rest/src/main/java/org/flowable/rest/service/api/history/HistoricProcessInstanceBaseResource.java:356

                break;

            case EQUALS_IGNORE_CASE:
                if (actualValue instanceof String) {
                    processInstanceQuery.variableValueEqualsIgnoreCase(variable.getName(), (String) actualValue);
                } else {
                    throw new FlowableIllegalArgumentException("Only string variable values are supported when ignoring casing, but was: " + actualValue.getClass().getName());
                }
                break;

            case NOT_EQUALS:
                processInstanceQuery.variableValueNotEquals(variable.getName(), actualValue);
                break;

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

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

            case GREATER_THAN:
                processInstanceQuery.variableValueGreaterThan(variable.getName(), actualValue);
                break;

            case GREATER_THAN_OR_EQUALS:
                processInstanceQuery.variableValueGreaterThanOrEqual(variable.getName(), actualValue);

View on GitHub (pinned to d6d39ce1c6)

Solutions

  1. Use EQUALS, GREATER_THAN, etc. for non-String variables and reserve LIKE for text
  2. Send the value as a JSON string when a textual pattern match is intended
  3. Convert the numeric/date variable's value to a String variable in the process definition if pattern search is required

Example fix

// before
{"name":"amount","type":"long","value":500,"variableOperation":"LIKE"}
// after
{"name":"description","value":"%refund%","variableOperation":"LIKE"}
Defensive patterns

Strategy: validation

Validate before calling

if (variable.variableOperation === 'LIKE' && typeof variable.value !== 'string') throw new Error('LIKE requires a string value');

Type guard

const isString = (v) => typeof v === 'string';

Try / catch

catch (e) { if (e.response && e.response.status === 400) { console.error(e.response.data.message); } throw e; }

Prevention

When it happens

Trigger: History process instance query requests with a variable whose variableOperation is LIKE but whose value is a number, boolean, date, or other non-String type.

Common situations: Querying numeric variables with wildcard patterns assuming implicit conversion; passing dates to LIKE expecting string formatting; generic query builders that reuse one value type across operations.

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

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/8b9ad5b6cd98b099. Report an issue: GitHub.