在做项目过程中，以前处理字符串时，总是以一些常见的符号作为分隔符，没遇到什么问题。最近在处理用户登录过滤IP时，才发现 用小数点作为分隔符有问题，无法实现想要的效果。代码如下：

String ip = "192.168.1.1";

String[] ips = ip.split(".");// 我们经常用 分号，逗号，顿号以及其他一些符号 都很正常

刚开始以为是split方法对此有特殊要求，小数点有特殊用途，不能作为分隔符。最后查询了下 jdk api才发现 不是split方法的问题。是模式匹配的事。

    我们在调用split(".")方法时，程序都会以中间符号作为模式匹配的字符。例如 ：ip.split(".")时，程序会用“.”在ip中进行匹配。但是在 Pattern 类中方法中，有些符号有特殊定义。例如：小数点“.”代表匹配的是任意字符，而不是小数点了。这些我们在正则表达式中 经常遇到。如果想使用小数点 必须加上“\\”

String[] ips = ip.split("\\."); 就能达到想要的效果了。以小数点作为分隔符。

 

下面贴出的是 Pattern类中的一些 特殊字符。大家可以参考下，以便以后学习

Construct	Matches
Characters
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)
Predefined character classes
.	Any character (may or may not match line terminators)
\d	A digit: [0-9]
\D	A non-digit: [^0-9]
\s	A whitespace character: [ \t\n\x0B\f\r]
\S	A non-whitespace character: [^\s]
\w	A word character: [a-zA-Z_0-9]
\W	A non-word character: [^\w]
POSIX character classes (US-ASCII only)
\p{Lower}	A lower-case alphabetic character: [a-z]
\p{Upper}	An upper-case alphabetic character:[A-Z]
\p{ASCII}	All ASCII:[\x00-\x7F]
\p{Alpha}	An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}	A decimal digit: [0-9]
\p{Alnum}	An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph}	A visible character: [\p{Alnum}\p{Punct}]
\p{Print}	A printable character: [\p{Graph}\x20]
\p{Blank}	A space or a tab: [ \t]
\p{Cntrl}	A control character: [\x00-\x1F\x7F]
\p{XDigit}	A hexadecimal digit: [0-9a-fA-F]
\p{Space}	A whitespace character: [ \t\n\x0B\f\r]
java.lang.Character classes (simple java character type)
\p{javaLowerCase}	Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase}	Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace}	Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored}	Equivalent to java.lang.Character.isMirrored()
Classes for Unicode blocks and categories
\p{InGreek}	A character in the Greek block (simple block)
\p{Lu}	An uppercase letter (simple category)
\p{Sc}	A currency symbol
\P{InGreek}	Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]	Any letter except an uppercase letter (subtraction)
Boundary matchers
^	The beginning of a line
$	The end of a line
\b	A word boundary
\B	A non-word boundary
\A	The beginning of the input
\G	The end of the previous match
\Z	The end of the input but for the final terminator, if any
\z	The end of the input
Greedy quantifiers
X?	X, once or not at all
X*	X, zero or more times
X+	X, one or more times
X{n}	X, exactly n times
X{n,}	X, at least n times
X{n,m}	X, at least n but not more than m times
Reluctant quantifiers
X??	X, once or not at all
X*?	X, zero or more times
X+?	X, one or more times
X{n}?	X, exactly n times
X{n,}?	X, at least n times
X{n,m}?	X, at least n but not more than m times
Possessive quantifiers
X?+	X, once or not at all
X*+	X, zero or more times
X++	X, one or more times
X{n}+	X, exactly n times
X{n,}+	X, at least n times
X{n,m}+	X, at least n but not more than m times
Logical operators
XY	X followed by Y
X|Y	Either X or Y
(X)	X, as a capturing group
Back references
\n	Whatever the nth capturing group matched
Quotation
\	Nothing, but quotes the following character
\Q	Nothing, but quotes all characters until \E
\E	Nothing, but ends quoting started by \Q
Special constructs (non-capturing)
(?:X)	X, as a non-capturing group
(?idmsux-idmsux)	Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)	X, as a non-capturing group with the given flags i d m s u x on - off
(?=X)	X, via zero-width positive lookahead
(?!X)	X, via zero-width negative lookahead
(?<=X)	X, via zero-width positive lookbehind
(?<!X)	X, via zero-width negative lookbehind
(?>X)	X, as an independent, non-capturing group

Construct	Matches
Characters
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)
Predefined character classes
.	Any character (may or may not match line terminators)
\d	A digit: [0-9]
\D	A non-digit: [^0-9]
\s	A whitespace character: [ \t\n\x0B\f\r]
\S	A non-whitespace character: [^\s]
\w	A word character: [a-zA-Z_0-9]
\W	A non-word character: [^\w]
POSIX character classes (US-ASCII only)
\p{Lower}	A lower-case alphabetic character: [a-z]
\p{Upper}	An upper-case alphabetic character:[A-Z]
\p{ASCII}	All ASCII:[\x00-\x7F]
\p{Alpha}	An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}	A decimal digit: [0-9]
\p{Alnum}	An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph}	A visible character: [\p{Alnum}\p{Punct}]
\p{Print}	A printable character: [\p{Graph}\x20]
\p{Blank}	A space or a tab: [ \t]
\p{Cntrl}	A control character: [\x00-\x1F\x7F]
\p{XDigit}	A hexadecimal digit: [0-9a-fA-F]
\p{Space}	A whitespace character: [ \t\n\x0B\f\r]
java.lang.Character classes (simple java character type)
\p{javaLowerCase}	Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase}	Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace}	Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored}	Equivalent to java.lang.Character.isMirrored()
Classes for Unicode blocks and categories
\p{InGreek}	A character in the Greek block (simple block)
\p{Lu}	An uppercase letter (simple category)
\p{Sc}	A currency symbol
\P{InGreek}	Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]	Any letter except an uppercase letter (subtraction)
Boundary matchers
^	The beginning of a line
$	The end of a line
\b	A word boundary
\B	A non-word boundary
\A	The beginning of the input
\G	The end of the previous match
\Z	The end of the input but for the final terminator, if any
\z	The end of the input
Greedy quantifiers
X?	X, once or not at all
X*	X, zero or more times
X+	X, one or more times
X{n}	X, exactly n times
X{n,}	X, at least n times
X{n,m}	X, at least n but not more than m times
Reluctant quantifiers
X??	X, once or not at all
X*?	X, zero or more times
X+?	X, one or more times
X{n}?	X, exactly n times
X{n,}?	X, at least n times
X{n,m}?	X, at least n but not more than m times
Possessive quantifiers
X?+	X, once or not at all
X*+	X, zero or more times
X++	X, one or more times
X{n}+	X, exactly n times
X{n,}+	X, at least n times
X{n,m}+	X, at least n but not more than m times
Logical operators
XY	X followed by Y
X|Y	Either X or Y
(X)	X, as a capturing group
Back references
\n	Whatever the nth capturing group matched
Quotation
\	Nothing, but quotes the following character
\Q	Nothing, but quotes all characters until \E
\E	Nothing, but ends quoting started by \Q
Special constructs (non-capturing)
(?:X)	X, as a non-capturing group
(?idmsux-idmsux)	Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)	X, as a non-capturing group with the given flags i d m s u x on - off
(?=X)	X, via zero-width positive lookahead
(?!X)	X, via zero-width negative lookahead
(?<=X)	X, via zero-width positive lookbehind
(?<!X)	X, via zero-width negative lookbehind
(?>X)	X, as an independent, non-capturing group

Construct	Matches
Characters
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)
Predefined character classes
.	Any character (may or may not match line terminators)
\d	A digit: [0-9]
\D	A non-digit: [^0-9]
\s	A whitespace character: [ \t\n\x0B\f\r]
\S	A non-whitespace character: [^\s]
\w	A word character: [a-zA-Z_0-9]
\W	A non-word character: [^\w]
POSIX character classes (US-ASCII only)
\p{Lower}	A lower-case alphabetic character: [a-z]
\p{Upper}	An upper-case alphabetic character:[A-Z]
\p{ASCII}	All ASCII:[\x00-\x7F]
\p{Alpha}	An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}	A decimal digit: [0-9]
\p{Alnum}	An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph}	A visible character: [\p{Alnum}\p{Punct}]
\p{Print}	A printable character: [\p{Graph}\x20]
\p{Blank}	A space or a tab: [ \t]
\p{Cntrl}	A control character: [\x00-\x1F\x7F]
\p{XDigit}	A hexadecimal digit: [0-9a-fA-F]
\p{Space}	A whitespace character: [ \t\n\x0B\f\r]
java.lang.Character classes (simple java character type)
\p{javaLowerCase}	Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase}	Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace}	Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored}	Equivalent to java.lang.Character.isMirrored()
Classes for Unicode blocks and categories
\p{InGreek}	A character in the Greek block (simple block)
\p{Lu}	An uppercase letter (simple category)
\p{Sc}	A currency symbol
\P{InGreek}	Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]	Any letter except an uppercase letter (subtraction)
Boundary matchers
^	The beginning of a line
$	The end of a line
\b	A word boundary
\B	A non-word boundary
\A	The beginning of the input
\G	The end of the previous match
\Z	The end of the input but for the final terminator, if any
\z	The end of the input
Greedy quantifiers
X?	X, once or not at all
X*	X, zero or more times
X+	X, one or more times
X{n}	X, exactly n times
X{n,}	X, at least n times
X{n,m}	X, at least n but not more than m times
Reluctant quantifiers
X??	X, once or not at all
X*?	X, zero or more times
X+?	X, one or more times
X{n}?	X, exactly n times
X{n,}?	X, at least n times
X{n,m}?	X, at least n but not more than m times
Possessive quantifiers
X?+	X, once or not at all
X*+	X, zero or more times
X++	X, one or more times
X{n}+	X, exactly n times
X{n,}+	X, at least n times
X{n,m}+	X, at least n but not more than m times
Logical operators
XY	X followed by Y
X|Y	Either X or Y
(X)	X, as a capturing group
Back references
\n	Whatever the nth capturing group matched
Quotation
\	Nothing, but quotes the following character
\Q	Nothing, but quotes all characters until \E
\E	Nothing, but ends quoting started by \Q
Special constructs (non-capturing)
(?:X)	X, as a non-capturing group
(?idmsux-idmsux)	Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)	X, as a non-capturing group with the given flags i d m s u x on - off
(?=X)	X, via zero-width positive lookahead
(?!X)	X, via zero-width negative lookahead
(?<=X)	X, via zero-width positive lookbehind
(?<!X)	X, via zero-width negative lookbehind
(?>X)	X, as an independent, non-capturing group

Construct	Matches
Characters
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)

Construct	Matches
Characters
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)

Construct   Matches 【匹配】
Characters
x            The character x
\\           The backslash character
\0n          The character with octal value 0n (0 <= n <= 7)
\0nn         The character with octal value 0nn (0 <= n <= 7)
\0mnn        The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh         The character with hexadecimal value 0xhh
\uhhhh       The character with hexadecimal value 0xhhhh
\t           The tab character ('\u0009')
\n           The newline (line feed) character ('\u000A')
\r           The carriage-return character ('\u000D')
\f           The form-feed character ('\u000C')
\a           The alert (bell) character ('\u0007')
\e           The escape character ('\u001B')
\cx          The control character corresponding to x
 
Character classes
[abc]     a, b, or c (simple class)
[^abc]    Any character except a, b, or c (negation)
[a-zA-Z]      a through z or A through Z, inclusive (range)
[a-d[m-p]]     a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]    d, e, or f (intersection)
[a-z&&[^bc]]    a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]     a through z, and not m through p: [a-lq-z](subtraction)
 
Predefined character classes
.     Any character (may or may not match line terminators) 【如何字符】
\d    A digit: [0-9]
\D    A non-digit: [^0-9]
\s    A whitespace character: [ \t\n\x0B\f\r]
\S    A non-whitespace character: [^\s]
\w    A word character: [a-zA-Z_0-9]
\W    A non-word character: [^\w]
 
POSIX character classes (US-ASCII only)
\p{Lower}    A lower-case alphabetic character: [a-z]
\p{Upper}    An upper-case alphabetic character:[A-Z]
\p{ASCII}    All ASCII:[\x00-\x7F]
\p{Alpha}    An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}    A decimal digit: [0-9]
\p{Alnum}    An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}    Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph}    A visible character: [\p{Alnum}\p{Punct}]
\p{Print}    A printable character: [\p{Graph}\x20]
\p{Blank}    A space or a tab: [ \t]
\p{Cntrl}    A control character: [\x00-\x1F\x7F]
\p{XDigit}   A hexadecimal digit: [0-9a-fA-F]
\p{Space}    A whitespace character: [ \t\n\x0B\f\r]
 
java.lang.Character classes (simple java character type)
\p{javaLowerCase}   Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase}   Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace}   Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored}   Equivalent to java.lang.Character.isMirrored()
 
Classes for Unicode blocks and categories
\p{InGreek}    A character in the Greek block (simple block)
\p{Lu}         An uppercase letter (simple category)
\p{Sc}         A currency symbol
\P{InGreek}    Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]  Any letter except an uppercase letter (subtraction)
 
Boundary matchers
^ The beginning of a line
$ The end of a line
\b A word boundary
\B A non-word boundary
\A The beginning of the input
\G The end of the previous match
\Z The end of the input but for the final terminator, if any
\z The end of the input
 
Greedy quantifiers
X?     X,once or not at all
X*     X, zero or more times
X+     X,one or more times
X{n}   X,exactly n times
X{n,}  X,at least n times
X{n,m} X,at least n but not more than m times
 
Reluctant quantifiers
X??    X, once or not at all
X*?    X, zero or more times
X+?    X, one or more times
X{n}?    X, exactly n times
X{n,}?    X, at least n times
X{n,m}?    X, at least n but not more than m times
 
Possessive quantifiers
X?+    X, once or not at all
X*+    X, zero or more times
X++    X, one or more times
X{n}+    X, exactly n times
X{n,}+    X, at least n times
X{n,m}+    X, at least n but not more than m times
 
Logical operators
XY X followed by Y
X|Y Either X or Y
(X) X, as a capturing group
 
Back references
\n Whatever the nth capturing group matched
 
Quotation
\ Nothing, but quotes the following character
\Q Nothing, but quotes all characters until \E
\E Nothing, but ends quoting started by \Q
 
Special constructs (non-capturing)
(?:X)  X, as a non-capturing group
(?idmsux-idmsux)  Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)   X, as a non-capturing group with the given flags i d m s u x on - off
(?=X)   X, via zero-width positive lookahead
(?!X)   X, via zero-width negative lookahead
(?<=X)   X, via zero-width positive lookbehind
(?<!X)  X, via zero-width negative lookbehind
(?>X)  X, as an independent, non-capturing group