Regular expression for not empty

Question

I need a Java regular expression, which checks that the given String is not Empty. However the expression should ingnore if the user has accidentally given whitespace in the beginning of the input, but allow whitespaces later on. Also the expression should allow scandinavian letters, Ä,Ö and so on, both lower and uppercase.

I have googled, but nothing seems ro quite fit on my needs. Please help.

score 24 · Answer 1 · answered Dec 15 '10 at 15:37

24

You can also use positive lookahead assertion to assert that the string has atleast one non-whitespace character:

^(?=\s*\S).*$

In Java you need

"^(?=\\s*\\S).*$"

answered Dec 15 '10 at 15:37

codaddict

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+1 because sometimes it's still easier to use a regexp than a method. Ex: @Pattern for JSR-303 validation when Hibernate's @NotBlank can't be used. Nice job optimizing – Peter Davis Apr 12 '11 at 21:43

score 15 · Answer 2 · edited Nov 08 '12 at 12:47

15

For a non empty String use .+.

edited Nov 08 '12 at 12:47

answered Nov 08 '12 at 12:27

Lavish

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score 5 · Answer 3 · answered Dec 15 '10 at 10:19

5

This should work:

/^\s*\S.*$/

but a regular expression might not be the best solution depending on what else you have in mind.

answered Dec 15 '10 at 10:19

sjngm

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@jaana: This answer is in JavaScript syntax; in Java it would be `"^\\s*\\S.*$"`. – Tim Pietzcker Dec 15 '10 at 10:41

score 4 · Answer 4 · answered Dec 15 '10 at 10:19

4

^\s*\S

(skip any whitespace at the start, then match something that's not whitespace)

answered Dec 15 '10 at 10:19

The Archetypal Paul

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It does not allow whitespaces later on? – jaana Dec 15 '10 at 10:24
Depends if you match against the whole string or not. If you want to match against the whole string, add .*$ to the end. But unless you must use a regex, as others have pointed out, trim is more direct. – The Archetypal Paul Dec 15 '10 at 10:27
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In fact even bare \S is enough. You do not need any anchors at start it either contains non-whitespace somewhere or not. – Muxecoid Dec 15 '10 at 10:30
@Muxecoid, yep, that's even simpler – The Archetypal Paul Dec 15 '10 at 10:31

score 4 · Answer 5 · edited Feb 09 '12 at 23:26

4

For testing on non-empty input I use:

private static final String REGEX_NON_EMPTY = ".*\\S.*"; 
// any number of whatever character followed by 1 or more non-whitespace chars, followed by any number of whatever character

edited Feb 09 '12 at 23:26

javanna

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answered Feb 09 '12 at 19:04

Rob Krabbendam

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score 2 · Answer 6 · answered Dec 15 '10 at 10:22

2

You don't need a regexp for this. This works, is clearer and faster:

if(myString.trim().length() > 0)

answered Dec 15 '10 at 10:22

Michael Borgwardt

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score -3 · Answer 7 · answered Dec 15 '10 at 10:30

It's faster to create a method for this rather than using regular expression

/**
 * This method takes String as parameter
 * and checks if it is null or empty.
 * 
 * @param value - The value that will get checked. 
 * Returns the value of "".equals(value). 
 * This is also trimmed, so that "     " returns true
 * @return - true if object is null or empty
 */
public static boolean empty(String value) {
    if(value == null)
        return true;

    return "".equals(value.trim());
}

what about String.IsNullOrEmpty(value) ? – L.Grillo Sep 09 '14 at 12:27 — L.Grillo, Sep 09 '14 at 12:27

Regular expression for not empty

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