java中字符串以小数点作为分…
原文地址：java中字符串以小数点作为分隔符问题
作者：行云流水
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 |
| 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 | 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: [ tnx0Bfr] |
| 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-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 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 nthcapturing 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 |
| 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 | 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: [ tnx0Bfr] |
| 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-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 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 nthcapturing 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 |
| 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 | 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: [ tnx0Bfr] |
| 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-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 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 nthcapturing 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 |
| 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 | 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 |
| 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 | 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) |
Characters
x The character x
\ The backslash 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 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: [ tnx0Bfr]
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-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 and categories
p{InGreek} A character in the Greek block (simple block)
p{Lu} An uppercase letter (simple category)
p{Sc}