Question

I know i can match numbers with Pattern.compile("\\d*");

But it doesn’t handle the long min/max values.

For performence issues related to exceptions i do not want to try to parse the long unless it is really a long.

if ( LONG_PATTERN.matcher(timestampStr).matches() ) {
    long timeStamp = Long.parseLong(timestampStr);
    return new Date(timeStamp);
} else {
    LOGGER.error("Can't convert " + timestampStr + " to a Date because it is not a timestamp! -> ");
    return null;
}

I mean i do not want any try/catch block and i do not want to get exceptions raised for a long like “564654954654464654654567879865132154778” which is out of the size of a regular Java long.

Does someone has a pattern to handle this kind of need for the primitive java types?
Does the JDK provide something to handle it automatically?
Is there a fail-safe parsing mecanism in Java?

Thanks

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Edit: Please assume that the “bad long string” is not an exceptionnal case.
I’m not asking for a benchmark, i’m here for a regex representing a long and nothing more.
I’m aware of the additionnal time required by the regex check, but at least my long parsing will always be constant and never be dependent of the % of “bad long strings”

I can’t find the link again but there is a nice parsing benchmark on StackOverflow which clearly shows that reusing the sams compiled regex is really fast, a LOT faster than throwing an exception, thus only a small threshold of exceptions whould make the system slower than with the additionnal regex check.

Answer 1

The minimum avlue of a long is -9,223,372,036,854,775,808, and the maximum value is 9,223,372,036,854,775,807. So, a maximum of 19 digits. So, \d{1,19} should get you there, perhaps with an optional -, and with ^ and $ to match the ends of the string.

So roughly:

Pattern LONG_PATTERN = Pattern.compile("^-?\\d{1,19}$");

…or something along those lines, and assuming you don’t allow commas (or have already removed them).

As gexicide points out in the comments, the above allows a small (in comparison) range of invalid values, such as 9,999,999,999,999,999,999. You can get more complex with your regex, or just accept that the above will weed out the vast majority of invalid numbers and so you reduce the number of parsing exceptions you get.