flowable/flowable-engine · error · ParseException

'/' must be followed by an integer.

Error message

'/' must be followed by an integer.

What it means

Thrown when an increment '/' is specified but nothing valid follows it: the expression ends or the next character is a space/tab. The parser requires 'start/step' where step is an integer, e.g. '0/15' in the minutes field. A dangling '/' is a syntax error.

Solutions

  1. Provide the step integer after '/': '0/15', '*/5', '1/10'.
  2. Check for empty or whitespace-only step variables when the expression is built dynamically.
  3. Trim the expression and ensure no field ends with '/'.
  4. Use validateExpression on configuration load so bad cron strings fail at startup, not at first trigger.

Example fix

// before
new CronExpression("0 0/ * * * ?");
// after
new CronExpression("0 0/15 * * * ?");
Defensive patterns

Strategy: validation

Validate before calling

if (java.util.regex.Pattern.compile("/\\s").matcher(expr).find()) {
    throw new IllegalArgumentException("'/' must be followed by a step integer: " + expr);
}

Try / catch

try {
    new CronExpression(expr);
} catch (java.text.ParseException e) {
    if (e.getMessage().contains("'/' must be followed")) {
        throw new IllegalArgumentException("Dangling '/' in cron field: " + expr, e);
    }
}

Prevention

When it happens

Trigger: new CronExpression("0 0/ * * * ?") or "0 0/" — '/' at end of a field followed by whitespace; string truncation leaving a trailing '/'; joining fields with a trailing separator.

Common situations: Truncated expressions from config files cut at whitespace; dynamic building where the step variable was empty/null producing '0/' + ' ' + rest; hand-editing that deleted the step value.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/78fdaaeb7cbdc9d6. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-engine-common/src/main/java/org/flowable/common/engine/impl/calendar/CronExpression.java:636

                throw new ParseException("'?' can only be specified for Day-of-Month or Day-of-Week.", i);
            }
            if (type == DAY_OF_WEEK && !lastdayOfMonth) {
                int val = daysOfMonth.last();
                if (val == NO_SPEC_INT) {
                    throw new ParseException("'?' can only be specified for Day-of-Month -OR- Day-of-Week.", i);
                }
            }

            addToSet(NO_SPEC_INT, -1, 0, type);
            return i;
        }

        if (c == '*' || c == '/') {
            if (c == '*' && (i + 1) >= s.length()) {
                addToSet(ALL_SPEC_INT, -1, incr, type);
                return i + 1;
            } else if (c == '/' && ((i + 1) >= s.length() || s.charAt(i + 1) == ' ' || s.charAt(i + 1) == '\t')) {
                throw new ParseException("'/' must be followed by an integer.", i);
            } else if (c == '*') {
                i++;
            }
            c = s.charAt(i);
            if (c == '/') { // is an increment specified?
                i++;
                if (i >= s.length()) {
                    throw new ParseException("Unexpected end of string.", i);
                }

                incr = getNumericValue(s, i);

                i++;
                if (incr > 10) {
                    i++;
                }
                checkIncrementRange(incr, type, i);
            } else {

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