google/gson · error · NumberFormatException

{value}

Error message

{value}

What it means

Thrown internally by UtcDateTypeAdapter.parseInt() when the requested character range is out of bounds: beginIndex < 0, endIndex > string length, or beginIndex > endIndex. This indicates the date string is shorter than the parser expected at that field (e.g. a 2-digit month where the string ended early). It is a NumberFormatException whose message is the raw value; it propagates up and becomes part of the umbrella ParseException (error 7).

Source

Thrown at extras/src/main/java/com/google/gson/typeadapters/UtcDateTypeAdapter.java:258

   * @return true if the expected character exist at the given offset
   */
  private static boolean checkOffset(String value, int offset, char expected) {
    return (offset < value.length()) && (value.charAt(offset) == expected);
  }

  /**
   * Parse an integer located between 2 given offsets in a string
   *
   * @param value the string to parse
   * @param beginIndex the start index for the integer in the string
   * @param endIndex the end index for the integer in the string
   * @return the int
   * @throws NumberFormatException if the value is not a number
   */
  private static int parseInt(String value, int beginIndex, int endIndex)
      throws NumberFormatException {
    if (beginIndex < 0 || endIndex > value.length() || beginIndex > endIndex) {
      throw new NumberFormatException(value);
    }
    // use same logic as in Integer.parseInt() but less generic we're not supporting negative values
    int i = beginIndex;
    int result = 0;
    int digit;
    if (i < endIndex) {
      digit = Character.digit(value.charAt(i++), 10);
      if (digit < 0) {
        throw new NumberFormatException("Invalid number: " + value);
      }
      result = -digit;
    }
    while (i < endIndex) {
      digit = Character.digit(value.charAt(i++), 10);
      if (digit < 0) {
        throw new NumberFormatException("Invalid number: " + value);
      }
      result *= 10;

View on GitHub (pinned to 8b8628c656)

Solutions

1. Ensure the date string is complete and conforms to ISO-8601 length expectations (year=4, month=2, day=2, etc.).
2. Validate length/format with a regex before parsing (e.g. ^\d{4}-?\d{2}-?\d{2}.*).
3. Switch to a custom adapter using java.time with a lenient or optional-section pattern if input is variable.
4. Inspect the raw input shown in the wrapped ParseException to see where truncation occurred.

Example fix

// before: truncated date
String json = "\"2024\"";
Date d = gson.fromJson(json, Date.class); // ultimately JsonParseException

// after: full ISO-8601 date
String json = "\"2024-01-01T00:00:00Z\"";
Date d = gson.fromJson(json, Date.class);

// Reject truncated date strings before parsing
static void requireMinLength(String date, int min) {
  if (date == null || date.length() < min) {
    throw new IllegalArgumentException("Date too short (expected >= " + min + "): " + date);
  }
}

static boolean isCompleteIsoDate(String date) {
  // basic completeness check for yyyy-MM-ddThh:mm:ss[Z|+HH:mm]
  return date != null && date.length() >= 20 && date.matches("^\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}.*");
}

try {
  Date d = gson.fromJson(json, Date.class);
} catch (JsonParseException e) {
  Throwable c = e.getCause();
  if (c != null && c.getMessage() != null && c.getCause() instanceof NumberFormatException) {
    // truncated input; reject or pad/retry
  } else throw e;
}

When it happens

Trigger: A date string too short for the field being extracted, e.g. "2024" when the parser tries to read 2 more chars for the month; truncated payloads; off-by-one slicing from upstream processing. Ultimately surfaced as JsonParseException via the ParseException wrapper.

Common situations: Truncated timestamps; strings that were accidentally trimmed; non-ISO formats that happen to parse partially then run out of characters; encoding issues dropping bytes.

Related errors

• Invalid number: {value}
• No time zone indicator
• Invalid time zone indicator {timezoneIndicator}
• Failed to parse date [{input}]: {fail.getMessage()}
• Array must have size 1, but has size {size}

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/e8b0197508e6b2cb.json. Report an issue: GitHub.