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Preface

Regular expression is a powerful string manipulation tool, which can achieve complex format string matching, replacement, segmentation, search, etc.
Regular expressions are supported in various languages, such as: java, Javascript, python, etc. The syntax is universal.
Regular expressions are composed of various symbols, and the key point is to learn the use of these symbols.

Character match

Use [] to match a single character, () to match multiple words

symbol	usage
[abc]	Find any character in square brackets
[^abc]	Find any character not in square brackets
[0-9]	Find any number from 0-9
[a-z]	Find any character from lowercase a to z
(red\|blue\|green)	Find any item in parentheses

Beginning and end

^ Matches the beginning of a string, such as (^a) is to match a string beginning with the letter a
$ Matches the end of a string, for example (b$) matches a string ending with the letter b

Adding ^ and $ at the beginning and end of the regular expression can effectively match the complete string:

/^表达式$/

Metacharacter

symbol	usage
.	Find any single character, except for newlines
\w	Any letter or number or underscore, any one of [A-Za-z0-9_]
\W	Find non-word characters, equivalent to [^A_Za_z0_9_]
\d	Match a digit character, equivalent to [0-9]
\D	Match a non-digit character, equivalent to [^0-9]
\s	Matches any blank characters, including spaces, tabs, newlines, etc. Equivalent to [\f\n\r\t\v]
\S	Match any non-white space character, equivalent to [^\f\n\r\t\v]
\b	Match the word boundary, the position between the word and the space, such as'er\b' can match the "er" in "never", but not the "er" in "verb"
\B	Match non-word boundaries,'er\B' can match the'er' in'verb' but not the'er' in'never'
\0	Find NUL characters.
\n	Match a newline character
\f	Match a form feed
\r	Matches a carriage return
\t	Matches a tab
\ v	Matches a vertical tab
\xxx	Find a character specified by the octal number xxx
\ xdd	Find the character specified by the hexadecimal number dd
\ uxxxx	Find the Unicode character specified by xxxx in hexadecimal number.

quantifier

symbol	usage
n+	Matches any string containing at least one n
n*	Match zero or more strings of n
n?	Match zero or one string of n
n{x}	Match the sequence string containing x n
n {x, y}	Match at least x and at most y strings of n
n{x,}	Matches at least x strings
n$	Match strings ending in n
^n	Match strings starting with n
?=n	Match the specified n string immediately after it
?!n	Matches the n string that does not follow the specified

Commonly used regular expressions

Some common regular expressions
phone number

^1[3|4|5|7|8]\d{9}$

Decimal

^(-?\d+)(\.\d+)?$

email address

[a-zA-Z_]{1,}[0-9]{0,}@(([a-zA-z0-9]-*){1,}\\.){1,3}[a-zA-z\\-]{1,}

HTML tags

/<(.*)>.*<\/\1>|<(.*) \/>/

Chinese characters

[\u4e00-\u9fa5]

QQ number

(\d+)\.(\d+)\.(\d+)\.(\d+)

(\d+)\.(\d+)\.(\d+)\.(\d+)

Use regular expressions

Java implements regular expression matching API:

Pattern expression pattern
Matcher

Pattern class

Creation method

Pattern.compile(regEx)
忽略大小写
Pattern.compile(regEx, Pattern.CASE_INSENSITIVE);

Matcher class

Creation method

pattern对象.matcher(字符串)

Common method

boolean matches() whether to match the complete string

Email verification case

public static void main(String[] args) {
    // 要验证的字符串
    String str = "[email protected]";
    // 邮箱验证规则
    String regEx = "[a-zA-Z_]{1,}[0-9]{0,}@(([a-zA-z0-9]-*){1,}\\.){1,3}[a-zA-z\\-]{1,}";
    // 编译正则表达式
    Pattern pattern = Pattern.compile(regEx);
    Matcher matcher = pattern.matcher(str);
    // 字符串是否与正则表达式相匹配
    boolean rs = matcher.matches();
    System.out.println(rs);
}

Common method

Whether boolean find() can search the defined content in the string
String group(String name) returns the searched string content

Search the content of src in multiple img tags

String str = "<img src=\"http://www.xx.com/1.jpg\"><img src=\"http://www.xx.com/2.jpg\">";
Pattern pattern = Pattern.compile("<img src=\"(?<url>.+?)\">");
Matcher matcher = pattern.matcher(str);
while (matcher.find()) {
    System.out.println(matcher.group("url"));
}

String

Some methods in the String class also use regular expressions
such as:

String replaceAll(String regex,String replacement)
boolean matches(String regex)
String[] split(String regex)

Replace numbers with *

String str = "123456Java";
String str2 = str.replaceAll("\\d", "*");

Match phone number

String tel = "1567667443";
boolean matches = tel.matches("^1[3|4|5|7|8]\\d{9}$");

Split character

String words = "中国.湖北.武汉";
String[] strings = words.split("\\.");

End

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Java Basics 24~Regular Expressions