Whitespace Matching Regex - Java

Question

The Java API for regular expressions states that  s will match whitespace  So the regex   s  s should match two spaces   Pattern whitespace   Pattern compile    s  s    matcher   whitespace matcher modLine   while  matcher find    matcher replaceAll         The aim of this is to replace all instances of two consecutive whitespace with a single space  However this does not actually work   Am I having a grave misunderstanding of regexes or the term  whitespace

User · Answer

when I sended a question to a Regexbuddy (regex developer application) forum, I got more exact reply to my \s Java question:

"Message author: Jan Goyvaerts

In Java, the shorthands \s, \d, and \w only include ASCII characters. ... This is not a bug in Java, but simply one of the many things you need to be aware of when working with regular expressions. To match all Unicode whitespace as well as line breaks, you can use [\s\p{Z}] in Java. RegexBuddy does not yet support Java-specific properties such as \p{javaSpaceChar} (which matches the exact same characters as [\s\p{Z}]).

... \s\s will match two spaces, if the input is ASCII only. The real problem is with the OP's code, as is pointed out by the accepted answer in that question."

User · Answer

For Java  not php  not javascript  not anyother    txt replaceAll    p javaSpaceChar  2

User · Answer

For your purpose you can use this snnippet   import org apache commons lang3 StringUtils   StringUtils normalizeSpace string     This will normalize the spacing to single and will strip off the starting and trailing whitespaces as well   String sampleString    Hello    world    sampleString replaceAll    s 2             replaces exactly two consecutive spaces sampleString replaceAll    s 2              replaces two or more consecutive white spaces

User · Answer

Seems to work for me   String s      a   b      c   System out println         s replaceAll    s  s                   will print     a  b   c    I think you intended to do this instead of your code   Pattern whitespace   Pattern compile    s  s    Matcher matcher   whitespace matcher s   String result       if  matcher find          result   matcher replaceAll          System out println result

User · Answer

Java has evolved since this issue was first brought up   You can match all manner of unicode space characters by using the  p Zs  group   Thus if you wanted to replace one or more exotic spaces with a plain space you could do this   String txt    whatever my string is   txt replaceAll    p Zs            Also worth knowing  if you ve used the trim   string function you should take a look at the  relatively new  strip    stripLeading    and stripTrailing   functions on strings   The can help you trim off all sorts of squirrely white space characters   For more information on what what space is included  see Java s Character isWhitespace   function

User · Answer

Yeah  you need to grab the result of matcher replaceAll     String result   matcher replaceAll       System out println result

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Pattern whitespace   Pattern compile    s  s    matcher   whitespace matcher modLine    boolean flag   true  while flag       Update your original search text with the result of the replace  modLine   matcher replaceAll          reset matcher to look at this  new  text  matcher   whitespace matcher modLine      search again     and if no match   set flag to false to exit  else run again  if  matcher find        flag   false

User · Answer

You can   t use  s in Java to match white space on its own native character set  because Java doesn   t support the Unicode white space property     even though doing so is strictly required to meet UTS 18   s RL1 2   What it does have is not standards-conforming  alas   Unicode defines 26 code points as  p White Space   20 of them are various sorts of  pZ GeneralCategory Separator  and the remaining 6 are  p Cc  GeneralCategory Control     White space is a pretty stable property  and those same ones have been around virtually forever  Even so   Java has no property that conforms to The Unicode Standard for these  so you instead have to use code like this   String whitespace chars                dummy empty string for homogeneity                                 u0009     CHARACTER TABULATION                              u000A     LINE FEED  LF                               u000B     LINE TABULATION                              u000C     FORM FEED  FF                               u000D     CARRIAGE RETURN  CR                               u0020     SPACE                              u0085     NEXT LINE  NEL                                u00A0     NO-BREAK SPACE                              u1680     OGHAM SPACE MARK                              u180E     MONGOLIAN VOWEL SEPARATOR                              u2000     EN QUAD                               u2001     EM QUAD                               u2002     EN SPACE                              u2003     EM SPACE                              u2004     THREE-PER-EM SPACE                              u2005     FOUR-PER-EM SPACE                              u2006     SIX-PER-EM SPACE                              u2007     FIGURE SPACE                              u2008     PUNCTUATION SPACE                              u2009     THIN SPACE                              u200A     HAIR SPACE                              u2028     LINE SEPARATOR                              u2029     PARAGRAPH SEPARATOR                              u202F     NARROW NO-BREAK SPACE                              u205F     MEDIUM MATHEMATICAL SPACE                              u3000     IDEOGRAPHIC SPACE                                      A  s that actually works for Java   s native character set  Unicode    String     whitespace charclass          whitespace chars               A  S that actually works for  Java   s native character set  Unicode    String not whitespace charclass          whitespace chars          Now you can use whitespace charclass       as the pattern in your replaceAll     Sorry    bout all that  Java   s regexes just don   t work very well on its own native character set  and so you really have to jump through exotic hoops to make them work    And if you think white space is bad  you should see what you have to do to get  w and  b to finally behave properly    Yes  it   s possible  and yes  it   s a mindnumbing mess   That   s being charitable  even  The easiest way to get a standards-comforming regex library for Java is to JNI over to ICU   s stuff  That   s what Google does for Android  because OraSun   s doesn   t measure up   If you don   t want to do that but still want to stick with Java  I have a front-end regex rewriting library I wrote that    fixes    Java   s patterns  at least to get them conform to the requirements of RL1 2a in UTS 18  Unicode Regular Expressions

User · Answer

Use of whitespace in RE is a pain  but I believe they work  The OP s problem can also be solved using StringTokenizer or the split   method  However  to use RE  uncomment the println   to view how the matcher is breaking up the String   here is a sample code   import java util regex     public class Two21WS       private String  str           private Pattern pattern   Pattern compile     s 2          multiple spaces      public Two21WS  String s                StringBuffer sb   new StringBuffer                Matcher matcher   pattern matcher  s               int startNext   0              while  matcher find  startNext                         if  startNext    0                              sb append  s substring  0  matcher start                          else                             sb append  s substring  startNext  matcher start                          sb append                            startNext   matcher end                          System out println   Start  end       matcher start        matcher end                                                    sb        sb toString                                      sb append  s substring  startNext                str   sb toString               public String toString                  return str             public static void main  String   args                String tester     a    b      cdef     gh  ij   kl               System out println   Initial        tester                      System out println   Two21WS        new Two21WS tester                It produces the following  compile with javac and run at the command prompt      java Two21WS Initial    a    b      cdef     gh  ij   kl  Two21WS    a b cdef gh ij kl

[java] Whitespace Matching Regex - Java

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