empty string checking not working as expected in java

Question

I am trying to check is string empty or not

Simply I have used apache.lang.StringUtils isNotBlank method to check

String str = " ";
System.out.println(StringUtils.isNotBlank(str)); // Output == true
System.out.println(StringUtils.isNotBlank(str.trim())); // Output == true
// But both expected as false

But every time its printing true.

Some other string its working fine but for above str value above code not working as expected.

You can try removing the whitespaces before checking - StringUtils.isNotBlank(str.trim()). — kevenlolo, Dec 14 '17 at 10:13
check if `Character.isWhiteSpace(str.chatAt(0))` returns true or not. — Eran, Dec 14 '17 at 10:15
Have you checked if this is perhaps a non-breaking space or a "hard space", i.e. alt-255? (Created in MS Word with ctrl-shift-space) — SurfMan, Dec 14 '17 at 10:17
Are you sure about the fully qualified name? Don't you use the newest version, where the name should be `org.apache.commons.lang3.StringUtils`. It btw works correctly there. — Tom, Dec 14 '17 at 10:21
Try this `System.out.println(Arrays.toString(str.getBytes()));` and show us what do you get in your console — Mustapha Belmokhtar, Dec 14 '17 at 10:22
@ShiladittyaChakraborty that answers your question, you should have got [32], in this case it is considered as a whitespace, a hidden character is in your `str` — Mustapha Belmokhtar, Dec 14 '17 at 10:27
@мυѕτавєւмo You may want to write you findings as an answer. `StringUtils.isNotBlank(new String(new byte[]{-96}))` actually returns `true`. — Tom, Dec 14 '17 at 10:31
@ShiladittyaChakraborty These questions might help you: 1. [How can I replace non-printable Unicode characters in Java?](https://stackoverflow.com/questions/6198986/how-can-i-replace-non-printable-unicode-characters-in-java) - 2. [Fastest way to strip all non-printable characters from a Java String](https://stackoverflow.com/questions/7161534/fastest-way-to-strip-all-non-printable-characters-from-a-java-string) — OH GOD SPIDERS, Dec 14 '17 at 10:45

score 4 · Answer 1 · edited Dec 14 '17 at 12:20

Some characters may appear to be whitespaces, but they aren't, or at least Java doesn't consider them as whitespaces. In your case, when you perform

System.out.println(Arrays.toString(str.getBytes()));

you got [-96] as output. -96 is an overflown byte value for 160 which is the no-breaking space character, but the Java Language Specification doesn't list that character as a whitespace character.
This why StringUtils.isNotBlank(str) returns true, because your String has non-whitespace characters. str.trim() removes whitespaces characters, thus it won't touch the existing no-breaking space.

You can reproduce that by manually creating a String with that character:

StringUtils.isNotBlank(new String(new byte[]{-96}));

or

StringUtils.isNotBlank(new String(new byte[]{(byte) 160}));

Both versions will yield true.

I took the liberty to add an explanation about the character in OPs String. Please review my changes :). — Tom, Dec 14 '17 at 12:20

Tim Biegeleisen · Answer 2 · 2017-12-14T10:32:21.987

You could try checking the length of the string after removing all whitespace:

String input = " ";
if (input != null && input.replaceAll("\\s+", "").length() > 0) {
    System.out.println("Not empty.");
}
else {
    System.out.println("Empty");
}

I offer this an alternative to using the Apache library. The logic is that a non empty string is any string which is not null and which has at least one non whitespace character in it.

empty string checking not working as expected in java

2 Answers2