10 Java Regular Expression Examples You Should Know

转自
http://www.mkyong.com/regular-expressions/10-java-regular-expression-examples-you-should-know/


Regular expression is an art of the programing, it’s hard to debug , learn and understand, but the powerful features are still attract many developers to code regular expression. Let’s explore the following 10 practical regular expression ~ enjoy
1. Username Regular Expression Pattern

^[a-z0-9_-]{3,15}$

^                    # Start of the line
  [a-z0-9_-]      # Match characters and symbols in the list, a-z, 0-9 , underscore , hyphen
             {3,15}  # Length at least 3 characters and maximum length of 15
$                    # End of the line

==> See the explanation and example here
2. Password Regular Expression Pattern

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})

( # Start of group
  (?=.*\d) #   must contains one digit from 0-9
  (?=.*[a-z]) #   must contains one lowercase characters
  (?=.*[A-Z]) #   must contains one uppercase characters
  (?=.*[@#$%]) #   must contains one special symbols in the list "@#$%"
              . #     match anything with previous condition checking
                {6,20} #        length at least 6 characters and maximum of 20
) # End of group

==> See the explanation and example here
3. Hexadecimal Color Code Regular Expression Pattern

^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$

^ #start of the line
# #  must constains a "#" symbols
( #  start of group #1
  [A-Fa-f0-9]{6} #    any strings in the list, with length of 6
  | #    ..or
  [A-Fa-f0-9]{3} #    any strings in the list, with length of 3
) #  end of group #1
$ #end of the line

==> See the explanation and example here
4. Email Regular Expression Pattern

^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9]+
(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$

^ #start of the line
  [_A-Za-z0-9-]+ #  must start with string in the bracket [ ], must contains one or more (+)
  ( #  start of group #1
    \\.[_A-Za-z0-9-]+ #     follow by a dot "." and string in the bracket [ ], must contains one or more (+)
  )* #  end of group #1, this group is optional (*)
    @ #     must contains a "@" symbol
     [A-Za-z0-9]+       #        follow by string in the bracket [ ], must contains one or more (+)
      ( #    start of group #2 - first level TLD checking
       \\.[A-Za-z0-9]+  #      follow by a dot "." and string in the bracket [ ], must contains one or more (+)
      )* #    end of group #2, this group is optional (*)
      ( #    start of group #3 - second level TLD checking
       \\.[A-Za-z]{2,}  #      follow by a dot "." and string in the bracket [ ], with minimum length of 2
      ) #    end of group #3
$ #end of the line

==> See the explanation and example here
5. Image File Extension Regular Expression Pattern

([^\s]+(\.(?i)(jpg|png|gif|bmp))$)

( #Start of the group #1
[^\s]+ #  must contains one or more anything (except white space)
       ( #    start of the group #2
         \. # follow by a dot "."
         (?i) # ignore the case sensitive checking
             ( #   start of the group #3
              jpg #     contains characters "jpg"
              | #     ..or
              png #     contains characters "png"
              | #     ..or
              gif #     contains characters "gif"
              | #     ..or
              bmp #     contains characters "bmp"
             ) #   end of the group #3
       ) #     end of the group #2
  $ #  end of the string
) #end of the group #1

==> See the explanation and example here
6. IP Address Regular Expression Pattern

^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])$

^ #start of the line
( #  start of group #1
   [01]?\\d\\d? #    Can be one or two digits. If three digits appear, it must start either 0 or 1
#    e.g ([0-9], [0-9][0-9],[0-1][0-9][0-9])
    | #    ...or
   2[0-4]\\d #    start with 2, follow by 0-4 and end with any digit (2[0-4][0-9])
    |           #    ...or
   25[0-5]      #    start with 2, follow by 5 and end with 0-5 (25[0-5])
) #  end of group #2
  \.            #  follow by a dot "."
....            # repeat with 3 time (3x)
$ #end of the line

==> See the explanation and example here
7. Time Format Regular Expression Pattern
Time in 12-Hour Format Regular Expression Pattern

(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)

( #start of group #1
1[012] #  start with 10, 11, 12
| #  or
[1-9] #  start with 1,2,...9
) #end of group #1
: #    follow by a semi colon (:)
  [0-5][0-9] #   follow by 0..5 and 0..9, which means 00 to 59
            (\\s)? #        follow by a white space (optional)
                  (?i) #          next checking is case insensitive
                      (am|pm) #            follow by am or pm

==> See the explanation and example here
Time in 24-Hour Format Regular Expression Pattern

([01]?[0-9]|2[0-3]):[0-5][0-9]

( #start of group #1
[01]?[0-9] #  start with 0-9,1-9,00-09,10-19
| #  or
2[0-3] #  start with 20-23
) #end of group #1
: #  follow by a semi colon (:)
  [0-5][0-9] #    follow by 0..5 and 0..9, which means 00 to 59

==> See the explanation and example here
8. Date Format (dd/mm/yyyy) Regular Expression Pattern

(0?[1-9]|[12][0-9]|3[01])/(0?[1-9]|1[012])/((19|20)\\d\\d)

( #start of group #1
0?[1-9] #  01-09 or 1-9
|                  #  ..or
[12][0-9] #  10-19 or 20-29
| #  ..or
3[01] #  30, 31
) #end of group #1
  / #  follow by a "/"
   ( #    start of group #2
    0?[1-9] # 01-09 or 1-9
    | # ..or
    1[012] # 10,11,12
    ) #    end of group #2
     / # follow by a "/"
      ( #   start of group #3
       (19|20)\\d\\d #     19[0-9][0-9] or 20[0-9][0-9]
       ) #   end of group #3

==> See the explanation and example here
9. HTML tag Regular Expression Pattern

<("[^"]*"|'[^']*'|[^'">])*>

<   #start with opening tag "<"
( #   start of group #1
   "[^"]*" # only two double quotes are allow - "string"
   | # ..or
   '[^']*' # only two single quotes are allow - 'string'
   | # ..or
   [^'">] # cant contains one single quotes, double quotes and ">"
) #   end of group #1
* # 0 or more
> #end with closing tag ">"

==> See the explanation and example here
10. HTML links Regular Expression Pattern
HTML A tag Regular Expression Pattern

(?i)<a([^>]+)>(.+?)</a>

( #start of group #1
?i #  all checking are case insensive
) #end of group #1
<a              #start with "<a"
  ( #  start of group #2
    [^>]+ #     anything except (">"), at least one character
   ) #  end of group #2
  > #     follow by ">"
    (.+?) # match anything
         </a> #   end with "</a>

Extract HTML link Regular Expression Pattern

\s*(?i)href\s*=\s*(\"([^"]*\")|'[^']*'|([^'">\s]+));

\s*    #can start with whitespace
  (?i)    # all checking are case insensive
     href    #  follow by "href" word
        \s*=\s*    #   allows spaces on either side of the equal sign,
              (    #    start of group #1
               "([^"]*")   #      only two double quotes are allow - "string"
               |    #   ..or
               '[^']*'    #      only two single quotes are allow - 'string'
               |           #   ..or
               ([^'">]+)   #     cant contains one single / double quotes and ">"
      )    #    end of group #1

==> See the explanation and example here