String length differs from Javascript to Java code

Question

I've got a JSP page with a piece of Javascript validation code which limits to a certain amount of characters on submit. I'm using a <textarea> so I can't simply use a length attribute like in a <input type="text">.

I use document.getElementById("text").value.length to get the string length. I'm running Firefox 3.0 on Windows (but I've tested this behavior with IE 6 also). The form gets submitted to a J2EE servlet. In my Java servlet the string length of the parameter is larger than 2000!

I've noticed that this can easily be reproduced by adding carriage returns in the <textarea>. I've used Firebug to assert the length of the <textare> and it really is 2000 characters long. On the Java side though, the carriage returns get converted to UNIX style (\r\n, instead of \n), thus the string length differs!

Am I missing something obvious here or what ? If not, how would you reliably (cross-platform / browser) make sure that the <textarea> is limited.

Answer 1

Do you particularly care which line-endings are used? Why not just make the Java convert "\r\n" to "\n"? (Note that "\r\n" is the Windows style; "\n" is the Unix style.)

Alternatively, do the reverse when checking the length within the JavaScript.

Answer 2

Are you limiting it to 2000 chars so it fits inside an nvarchar(2000) column in a database? Otherwise maybe just allow a 2% overrun to be flexible on the Java side.

And Java should be using Unicode UTF16 to represent Strings. That /r must have got in there somewhere else, maybe a conversion in the web browser when submitting? Have you tried different browsers? On different platforms? You might just have to strip out the /rs.

Answer 3

This isn't really a Javascript (or Java) problem - both layers report an accurate length for the string they are dealing with. The problem in your case is that the string gets transformed during the HTTP transmission.

If you absolutely must ensure that the string doesn't exceed a certain length, you can mimic this transformation on the client by replacing every instance of "\n" with "\n\r" - but only for length verification purposes:

textarea.value.replace(/\n/g, "\n\r").length