What causes "'/' must be followed by an integer." in xuxueli/xxl-job?

Add a valid integer after the '/' (e.g., '*/5' instead of '*/').

xuxueli/xxl-job · error · ParseException

'/' must be followed by an integer.

Error message

'/' must be followed by an integer.

What it means

This error occurs when the parser encounters a '/' character that is not followed by a valid increment integer — specifically when '/' is at the end of the field, or followed by a space/tab. In cron syntax, '/' specifies a step/increment value (e.g., '*/5'), and it must be followed by a number.

Source

Thrown at xxl-job-admin/src/main/java/com/xxl/job/admin/business/scheduler/cron/CronExpression.java:643

                if (!daysOfMonth.isEmpty() && daysOfMonth.last() == 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 {

View on GitHub (pinned to e74c784f68)

Solutions

Add a valid integer after the '/' (e.g., '*/5' instead of '*/').
Remove the '/' if no increment is intended (use '*' alone).
Validate the cron string with a regex or cron validator before passing it to the constructor.

Example fix

// before
"*/ * * * * ?"
// after
"*/5 * * * * ?"

Defensive patterns

Strategy: validation

Validate before calling

// Reject fields where '/' is not followed by a digit
for (String field : cron.trim().split("\\s+")) {
    int slash = field.indexOf('/');
    if (slash != -1 && (slash + 1 >= field.length() || !Character.isDigit(field.charAt(slash + 1)))) {
        throw new IllegalArgumentException("'/' must be followed by an integer in: " + field);
    }
}

Type guard

boolean hasValidStep(String field) {
    int i = field.indexOf('/');
    return i == -1 || (i + 1 < field.length() && Character.isDigit(field.charAt(i + 1)));

Try / catch

try {
    new CronExpression(cron);
} catch (ParseException e) {
    if (e.getMessage().contains("'/' must be followed by an integer")) {
        // prompt user for a valid step value
    }
}

Prevention

Never end a cron field with '/'; always append a step integer.
When building cron strings programmatically, guard against empty increment segments.
Use a cron validator utility before persisting user-supplied expressions.

When it happens

Trigger: A cron field ending with '/' such as '*/' (string ends immediately after '/'), or '*/ ' where '/' is followed by whitespace. The parser checks (i+1) >= s.length() or s.charAt(i+1) is space/tab right after the '/' in the '*' or '/' handling branch.

Common situations: Truncated cron string from user input or a template that was incompletely filled, or a copy-paste that dropped the trailing increment digit.

Related errors

AI-assisted analysis of xuxueli/xxl-job@e74c784f68 (2026-08-14). Data as JSON: /api/errors/4b6365d84d268e13. Report an issue: GitHub.