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 | xThe character x\The backslash character nThe character with octal value0n(0 <= n <= 7) nnThe character with octal value0nn(0 <= n <= 7) mnnThe character with octal value0mnn(0 <= m <= 3,0 <= n <= 7)xhhThe character withhexadecimal value 0xhhuhhhhThe character withhexadecimal value 0xhhhhtThe tab character ('u0009')nThe newline (line feed) character('u000A')rThe carriage-return character('u000D')fThe form-feed character('u000C')aThe alert (bell) character('u0007')eThe escape character ('u001B')cxThe control character corresponding tox | Character classes | [abc]a, b, or c (simpleclass)[^abc]Any character except a, b,or c (negation)[a-zA-Z]a through z or Athrough Z, inclusive (range)[a-d[m-p]]a through d, or mthrough p: [a-dm-p] (union)[a-z&&[def]]d, e, or f(intersection)[a-z&&[^bc]]a through z, except forb and c: [ad-z] (subtraction)[a-z&&[^m-p]]a through z, and notm through p: [a-lq-z](subtraction) | Predefined character classes | .Any character (may or may not match line terminators)dA digit: [0-9]DA non-digit: [^0-9]sA whitespace character: [tnx0Bfr]SA non-whitespace character:[^s]wA word character: [a-zA-Z_0-9]WA non-word character: [^w] | POSIX character classes (US-ASCIIonly) | p{Lower}A lower-case alphabetic character:[a-z]p{Upper}An upper-case alphabeticcharacter:[A-Z]p{ASCII}All ASCII:[x00-x7F]p{Alpha}An alphabeticcharacter:[p{Lower}p{Upper}]p{Digit}A decimal digit: [0-9]p{Alnum}An alphanumericcharacter:[p{Alpha}p{Digit}]p{Punct}Punctuation: One of!"#$%&'()*+,-./:;<=>?@[]^_`{|}~p{Graph}A visible character:[p{Alnum}p{Punct}]p{Print}A printable character:[p{Graph}x20]p{Blank}A space or a tab: [ t]p{Cntrl}A control character:[x00-x1Fx7F]p{XDigit}A hexadecimal digit:[0-9a-fA-F]p{Space}A whitespace character: [tnx0Bfr] | java.lang.Character classes (simple java character type) | p{javaLowerCase}Equivalent to java.lang.Character.isLowerCase()p{javaUpperCase}Equivalent to java.lang.Character.isUpperCase()p{javaWhitespace}Equivalent to java.lang.Character.isWhitespace()p{javaMirrored}Equivalent to java.lang.Character.isMirrored() | Classes for Unicode blocks andcategories | p{InGreek}A character in theGreek block (simple block)p{Lu}An uppercase letter (simple category)p{Sc}A currency symbolP{InGreek}Any character except one in the Greek block(negation)[p{L}&&[^p{Lu}]] Any letter except an uppercase letter(subtraction) | Boundary matchers | ^The beginning of a line$The end of a linebA word boundaryBA non-word boundaryAThe beginning of the inputGThe end of the previous matchZThe end of the input but for the finalterminator, if anyzThe end of the input | Greedy quantifiers | X?X, once or not at allX*X, zero or more timesX+X, one or more timesX{n}X, exactly n timesX{n,}X, at least n timesX{n,m}X, at least n but not more thanm times | Reluctant quantifiers | X??X, once or not at allX*?X, zero or more timesX+?X, one or more timesX{n}?X, exactly n timesX{n,}?X, at least n timesX{n,m}?X, at least n but not more thanm times | Possessive quantifiers | X?+X, once or not at allX*+X, zero or more timesX++X, one or more timesX{n}+X, exactly n timesX{n,}+X, at least n timesX{n,m}+X, at least n but not more thanm times | Logical operators | XYX followed by YX|YEither X or Y(X)X, as a capturinggroup | Back references | nWhatever thenth capturinggroup matched | Quotation | Nothing, but quotes the followingcharacterQNothing, but quotes all characters untilEENothing, but ends quoting started byQ | 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-capturinggroup with the given flags id m s u x on - off(?=X)X, via zero-width positivelookahead(?!X)X, via zero-width negativelookahead(?<=X)X, via zero-width positivelookbehind(?<!X)X, via zero-width negativelookbehind(?>X)X, as an independent, non-capturinggroupConstruct | Matches | | Characters | xThe character x\The backslash character nThe character with octal value0n(0 <= n <= 7) nnThe character with octal value0nn(0 <= n <= 7) mnnThe character with octal value0mnn(0 <= m <= 3,0 <= n <= 7)xhhThe character withhexadecimal value 0xhhuhhhhThe character withhexadecimal value 0xhhhhtThe tab character ('u0009')nThe newline (line feed) character('u000A')rThe carriage-return character('u000D')fThe form-feed character('u000C')aThe alert (bell) character('u0007')eThe escape character ('u001B')cxThe control character corresponding tox | Character classes | [abc]a, b, or c (simpleclass)[^abc]Any character except a, b,or c (negation)[a-zA-Z]a through z or Athrough Z, inclusive (range)[a-d[m-p]]a through d, or mthrough p: [a-dm-p] (union)[a-z&&[def]]d, e, or f(intersection)[a-z&&[^bc]]a through z, except forb and c: [ad-z] (subtraction)[a-z&&[^m-p]]a through z, and notm through p: [a-lq-z](subtraction) | Predefined character classes | .Any character (may or may not match line terminators)dA digit: [0-9]DA non-digit: [^0-9]sA whitespace character: [tnx0Bfr]SA non-whitespace character:[^s]wA word character: [a-zA-Z_0-9]WA non-word character: [^w] | POSIX character classes (US-ASCIIonly) | p{Lower}A lower-case alphabetic character:[a-z]p{Upper}An upper-case alphabeticcharacter:[A-Z]p{ASCII}All ASCII:[x00-x7F]p{Alpha}An alphabeticcharacter:[p{Lower}p{Upper}]p{Digit}A decimal digit: [0-9]p{Alnum}An alphanumericcharacter:[p{Alpha}p{Digit}]p{Punct}Punctuation: One of!"#$%&'()*+,-./:;<=>?@[]^_`{|}~p{Graph}A visible character:[p{Alnum}p{Punct}]p{Print}A printable character:[p{Graph}x20]p{Blank}A space or a tab: [ t]p{Cntrl}A control character:[x00-x1Fx7F]p{XDigit}A hexadecimal digit:[0-9a-fA-F]p{Space}A whitespace character: [tnx0Bfr] | java.lang.Character classes (simple java character type) | p{javaLowerCase}Equivalent to java.lang.Character.isLowerCase()p{javaUpperCase}Equivalent to java.lang.Character.isUpperCase()p{javaWhitespace}Equivalent to java.lang.Character.isWhitespace()p{javaMirrored}Equivalent to java.lang.Character.isMirrored() | Classes for Unicode blocks andcategories | p{InGreek}A character in theGreek block (simple block)p{Lu}An uppercase letter (simple category)p{Sc}A currency symbolP{InGreek}Any character except one in the Greek block(negation)[p{L}&&[^p{Lu}]] Any letter except an uppercase letter(subtraction) | Boundary matchers | ^The beginning of a line$The end of a linebA word boundaryBA non-word boundaryAThe beginning of the inputGThe end of the previous matchZThe end of the input but for the finalterminator, if anyzThe end of the input | Greedy quantifiers | X?X, once or not at allX*X, zero or more timesX+X, one or more timesX{n}X, exactly n timesX{n,}X, at least n timesX{n,m}X, at least n but not more thanm times | Reluctant quantifiers | X??X, once or not at allX*?X, zero or more timesX+?X, one or more timesX{n}?X, exactly n timesX{n,}?X, at least n timesX{n,m}?X, at least n but not more thanm times | Possessive quantifiers | X?+X, once or not at allX*+X, zero or more timesX++X, one or more timesX{n}+X, exactly n timesX{n,}+X, at least n timesX{n,m}+X, at least n but not more thanm times | Logical operators | XYX followed by YX|YEither X or Y(X)X, as a capturinggroup | Back references | nWhatever thenth capturinggroup matched | Quotation | Nothing, but quotes the followingcharacterQNothing, but quotes all characters untilEENothing, but ends quoting started byQ | 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-capturinggroup with the given flags id m s u x on - off(?=X)X, via zero-width positivelookahead(?!X)X, via zero-width negativelookahead(?<=X)X, via zero-width positivelookbehind(?<!X)X, via zero-width negativelookbehind(?>X)X, as an independent, non-capturinggroupConstruct | Matches | | Characters | xThe character x\The backslash character nThe character with octal value0n(0 <= n <= 7) nnThe character with octal value0nn(0 <= n <= 7) mnnThe character with octal value0mnn(0 <= m <= 3,0 <= n <= 7)xhhThe character withhexadecimal value 0xhhuhhhhThe character withhexadecimal value 0xhhhhtThe tab character ('u0009')nThe newline (line feed) character('u000A')rThe carriage-return character('u000D')fThe form-feed character('u000C')aThe alert (bell) character('u0007')eThe escape character ('u001B')cxThe control character corresponding tox | Character classes | [abc]a, b, or c (simpleclass)[^abc]Any character except a, b,or c (negation)[a-zA-Z]a through z or Athrough Z, inclusive (range)[a-d[m-p]]a through d, or mthrough p: [a-dm-p] (union)[a-z&&[def]]d, e, or f(intersection)[a-z&&[^bc]]a through z, except forb and c: [ad-z] (subtraction)[a-z&&[^m-p]]a through z, and notm through p: [a-lq-z](subtraction) | Predefined character classes | .Any character (may or may not match line terminators)dA digit: [0-9]DA non-digit: [^0-9]sA whitespace character: [tnx0Bfr]SA non-whitespace character:[^s]wA word character: [a-zA-Z_0-9]WA non-word character: [^w] | POSIX character classes (US-ASCIIonly) | p{Lower}A lower-case alphabetic character:[a-z]p{Upper}An upper-case alphabeticcharacter:[A-Z]p{ASCII}All ASCII:[x00-x7F]p{Alpha}An alphabeticcharacter:[p{Lower}p{Upper}]p{Digit}A decimal digit: [0-9]p{Alnum}An alphanumericcharacter:[p{Alpha}p{Digit}]p{Punct}Punctuation: One of!"#$%&'()*+,-./:;<=>?@[]^_`{|}~p{Graph}A visible character:[p{Alnum}p{Punct}]p{Print}A printable character:[p{Graph}x20]p{Blank}A space or a tab: [ t]p{Cntrl}A control character:[x00-x1Fx7F]p{XDigit}A hexadecimal digit:[0-9a-fA-F]p{Space}A whitespace character: [tnx0Bfr] | java.lang.Character classes (simple java character type) | p{javaLowerCase}Equivalent to java.lang.Character.isLowerCase()p{javaUpperCase}Equivalent to java.lang.Character.isUpperCase()p{javaWhitespace}Equivalent to java.lang.Character.isWhitespace()p{javaMirrored}Equivalent to java.lang.Character.isMirrored() | Classes for Unicode blocks andcategories | p{InGreek}A character in theGreek block (simple block)p{Lu}An uppercase letter (simple category)p{Sc}A currency symbolP{InGreek}Any character except one in the Greek block(negation)[p{L}&&[^p{Lu}]] Any letter except an uppercase letter(subtraction) | Boundary matchers | ^The beginning of a line$The end of a linebA word boundaryBA non-word boundaryAThe beginning of the inputGThe end of the previous matchZThe end of the input but for the finalterminator, if anyzThe end of the input | Greedy quantifiers | X?X, once or not at allX*X, zero or more timesX+X, one or more timesX{n}X, exactly n timesX{n,}X, at least n timesX{n,m}X, at least n but not more thanm times | Reluctant quantifiers | X??X, once or not at allX*?X, zero or more timesX+?X, one or more timesX{n}?X, exactly n timesX{n,}?X, at least n timesX{n,m}?X, at least n but not more thanm times | Possessive quantifiers | X?+X, once or not at allX*+X, zero or more timesX++X, one or more timesX{n}+X, exactly n timesX{n,}+X, at least n timesX{n,m}+X, at least n but not more thanm times | Logical operators | XYX followed by YX|YEither X or Y(X)X, as a capturinggroup | Back references | nWhatever thenth capturinggroup matched | Quotation | Nothing, but quotes the followingcharacterQNothing, but quotes all characters untilEENothing, but ends quoting started byQ | 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-capturinggroup with the given flags id m s u x on - off(?=X)X, via zero-width positivelookahead(?!X)X, via zero-width negativelookahead(?<=X)X, via zero-width positivelookbehind(?<!X)X, via zero-width negativelookbehind(?>X)X, as an independent, non-capturinggroupConstruct | Matches | | Characters | xThe character x\The backslash character nThe character with octal value0n(0 <= n <= 7) nnThe character with octal value0nn(0 <= n <= 7) mnnThe character with octal value0mnn(0 <= m <= 3,0 <= n <= 7)xhhThe character withhexadecimal value 0xhhuhhhhThe character withhexadecimal value 0xhhhhtThe tab character ('u0009')nThe newline (line feed) character('u000A')rThe carriage-return character('u000D')fThe form-feed character('u000C')aThe alert (bell) character('u0007')eThe escape character ('u001B')cxThe control character corresponding tox | Character classes | [abc]a, b, or c (simpleclass)[^abc]Any character except a, b,or c (negation)[a-zA-Z]a through z or Athrough Z, inclusive (range)[a-d[m-p]]a through d, or mthrough p: [a-dm-p] (union)[a-z&&[def]]d, e, or f(intersection)[a-z&&[^bc]]a through z, except forb and c: [ad-z] (subtraction)[a-z&&[^m-p]]a through z, and notm through p: [a-lq-z](subtraction)Construct | Matches | | Characters | xThe character x\The backslash character nThe character with octal value0n(0 <= n <= 7) nnThe character with octal value0nn(0 <= n <= 7) mnnThe character with octal value0mnn(0 <= m <= 3,0 <= n <= 7)xhhThe character withhexadecimal value 0xhhuhhhhThe character withhexadecimal value 0xhhhhtThe tab character ('u0009')nThe newline (line feed) character('u000A')rThe carriage-return character('u000D')fThe form-feed character('u000C')aThe alert (bell) character('u0007')eThe escape character ('u001B')cxThe control character corresponding tox | Character classes | [abc]a, b, or c (simpleclass)[^abc]Any character except a, b,or c (negation)[a-zA-Z]a through z or Athrough Z, inclusive (range)[a-d[m-p]]a through d, or mthrough p: [a-dm-p] (union)[a-z&&[def]]d, e, or f(intersection)[a-z&&[^bc]]a through z, except forb and c: [ad-z] (subtraction)[a-z&&[^m-p]]a through z, and notm through p: [a-lq-z](subtraction)Construct
Matches 【匹配】
Characters
x The character x
\ Thebackslash character
n The character with octal value 0n (0 <= n<= 7)
nn The character with octal value 0nn (0 <= n<= 7)
mnn 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 Thenewline (line feed) character ('u000A')
r Thecarriage-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] Anycharacter 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 matchline terminators) 【如何字符】
d A digit:[0-9]
D Anon-digit: [^0-9]
s Awhitespace character: [ tnx0Bfr]
S Anon-whitespace character: [^s]
w A wordcharacter: [a-zA-Z_0-9]
W A non-wordcharacter: [^w]
POSIX character classes (US-ASCII only)
p{Lower} Alower-case alphabetic character: [a-z]
p{Upper} Anupper-case alphabetic character:[A-Z]
p{ASCII} AllASCII:[x00-x7F]
p{Alpha} Analphabetic character:[p{Lower}p{Upper}]
p{Digit} Adecimal digit: [0-9]
p{Alnum} Analphanumeric character:[p{Alpha}p{Digit}]
p{Punct} Punctuation: One of!"#$%&'()*+,-./:;<=>?@[]^_`{|}~
p{Graph} Avisible character: [p{Alnum}p{Punct}]
p{Print} Aprintable character: [p{Graph}x20]
p{Blank} Aspace or a tab: [ t]
p{Cntrl} Acontrol character: [x00-x1Fx7F]
p{XDigit} A hexadecimal digit:[0-9a-fA-F]
p{Space} Awhitespace character: [ tnx0Bfr]
java.lang.Character classes (simple java character type)
p{javaLowerCase} Equivalent tojava.lang.Character.isLowerCase()
p{javaUpperCase} Equivalent tojava.lang.Character.isUpperCase()
p{javaWhitespace} Equivalentto java.lang.Character.isWhitespace()
p{javaMirrored} Equivalent tojava.lang.Character.isMirrored()
Classes for Unicode blocks and categories
p{InGreek} Acharacter in the Greek block (simple block)
p{Lu} An uppercase letter (simple category)
p{Sc}