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  • 什么是 RegEx（正则表达式）模式？ 如何在 Java 中使用它？ 附上示例

什么是 RegEx（正则表达式）模式？ 如何在 Java 中使用它？ 附上示例

已发表: 2021-01-25
什么是 RegEx 模式（正则表达式）？如何在 Java 中使用它？

什么是正则表达式？

正则表达式是字符串的一种搜索模式。 java.util.regex用于将字符序列与 Java 中正则表达式指定的模式进行匹配的类。

您可以将正则表达式用于：

  • 搜索文本
  • 提取文本
  • 修改文本

让我们讨论一些基本语法：

正则表达式中的字符类：

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.    Dot , any character ( may or may not match line terminators , read on )
\ 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 ]

正则表达式中的量词：

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*       Match 0 or more times
+       Match 1 or more times
?        Match 1 or 0 times
{ n }      Match exactly n times
{ n , }    Match at least n times
{ n , m }    Match at least n but not more than m times

Java Split 也是一个 Regex 示例。

正则表达式中的元字符：

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\    Escape the next meta - character ( it becomes a normal / literal character )
^   Match the beginning of the line
.    Match any character ( except newline )
$    Match the end of the line ( or before newline at the end )
|    Alternation ( ‘ or ’ statement )
( )    Grouping
[ ]    Custom character class

让我们开始研究示例。 在下面的示例中，我们将介绍 5 个不同的正则表达式示例。

  1. 如何在 Java 中解析 uptime 命令结果
  2. 检查 URL 是否以特定扩展名结尾
  3. 检查是否存在有效 IP
  4. 正则表达式的 ReplaceAll() 示例
  5. 查找 SSN 是否有效
Java
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package crunchify . com . tutorial ;
 
import java . util . regex . Matcher ;
import java . util . regex . Pattern ;
 
/**
* @author Crunchify.com
*
*/
 
public class CrunchifyRegexTutorial {
 
public static void main ( String [ ] args ) {
crunchifyLoadAndAverageRegex ( ) ;
System . out . println ( "\n==========================\n" ) ;
 
crunchifyFindUrlPattern ( ) ;
System . out . println ( "\n==========================\n" ) ;
 
crunchifyFindIPMatcher ( ) ;
System . out . println ( "\n==========================\n" ) ;
 
crunchifyRegexReplaceAllExample ( ) ;
System . out . println ( "\n==========================\n" ) ;
 
crunchifyValidateSSN ( ) ;
}
 
// Find if SSN is valid
private static void crunchifyValidateSSN ( ) {
String ssn1 = "123-45-6789" ;
String ssn2 = "123-456-789" ;
String pattern = "^(\\d{3}-?\\d{2}-?\\d{4})$" ;
 
if ( ssn1 . matches ( pattern ) ) {
System . out . println ( "SSN " + ssn1 + " is valid" ) ;
} else {
System . out . println ( "SSN " + ssn1 + " is NOT valid" ) ;
}
 
if ( ssn2 . matches ( pattern ) ) {
System . out . println ( "SSN " + ssn2 + " is valid" ) ;
} else {
System . out . println ( "SSN " + ssn2 + " is NOT valid" ) ;
}
 
}
 
// ReplaceAll() Example
private static void crunchifyRegexReplaceAllExample ( ) {
String find = "Java" ;
String line = "This is Crunchify.com Java Tutorial." ;
String replace = "Spring MVC" ;
 
Pattern p = Pattern . compile ( find ) ;
Matcher m = p . matcher ( line ) ;
 
// This line will find "Java" and replace it with "Spring MVC"
line = m . replaceAll ( replace ) ;
System . out . println ( line ) ;
 
}
 
// Check if valid IP present
private static void crunchifyFindIPMatcher ( ) {
Pattern validIPPattern = Pattern . compile ( "^(?:[0-9]{1,3}\\.){3}[0-9]{1,3}$" ) ;
System . out . println ( "192.abc.0.1 : " + validIPPattern . matcher ( "192.abc.0.1" ) . find ( ) ) ;
System . out . println ( "192.168.0.1 : " + validIPPattern . matcher ( "192.168.0.1" ) . find ( ) ) ;
}
 
// Check if URL ends with specific extension
private static void crunchifyFindUrlPattern ( ) {
String pattern = ".*\\.(ico|jpg|png|gif|tif|bmp|JPG|PNG|GIF|TIF|BMP)" ;
Pattern r = Pattern . compile ( pattern ) ;
 
Matcher m = r . matcher ( "https://crunchify.com/favicon.ico" ) ;
if ( m . find ( ) ) {
System . out . println ( "URL pattern found" ) ;
} else {
System . out . println ( "URL pattern doesn't found" ) ;
}
 
}
 
// How to Parse "uptime" command result in Java
public static void crunchifyLoadAndAverageRegex ( ) {
Pattern uptimePattern = Pattern . compile ( "^.*\\s+load\\s+average:\\s+([\\d\\.]+),\\s+([\\d\\.]+),\\s+([\\d\\.]+)$" ) ;
 
String output = " 10:17:32 up 189 days, 18:49,  5 user,  load average: 2.07, 1.11, 1.16" ;
Matcher m = uptimePattern . matcher ( output ) ;
 
if ( m . matches ( ) ) {
final double crunchify1MinuteLoadAvg = Double . parseDouble ( m . group ( 1 ) ) ;
final double crunchify5eMinuteloadAvg = Double . parseDouble ( m . group ( 2 ) ) ;
final double crunchify15MinuteLoadAvg = Double . parseDouble ( m . group ( 3 ) ) ;
 
System . out . println ( "Load Average 1 min: " + crunchify1MinuteLoadAvg ) ;
System . out . println ( "Load Average 5 min: " + crunchify5eMinuteloadAvg ) ;
System . out . println ( "Load Average 15 min: " + crunchify15MinuteLoadAvg ) ;
} else {
System . out . println ( "no matches found" ) ;
}
 
}
}

输出：

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Load Average 1 min : 2.07
Load Average 5 min : 1.11
Load Average 15 min : 1.16
 
==========================
 
URL pattern found
 
==========================
 
192.abc.0.1 : false
192.168.0.1 : true
 
==========================
 
This is Crunchify . com Spring MVC Tutorial .
 
==========================
 
SSN 123 - 45 - 6789 is valid
SSN 123 - 456 - 789 is NOT valid

如何使用 Java 代码验证密码强度？

在下面找到我的条件：

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#   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
{ 8 , 25 } length at least 8 characters and maximum of 25

CrunchifyPasswordVerification.java

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package crunchify . com . tutorial ;
 
import java . util . ArrayList ;
import java . util . List ;
import java . util . regex . Matcher ;
import java . util . regex . Pattern ;
 
/**
* @author Crunchify.com
*
*/
public class CrunchifyPasswordVerification {
public static void main ( String [ ] args ) {
 
String pattern = "((?=.*[@!#$%])(?=.*[a-z])(?=.*[A-Z])(?=.*\\d).{8,22})" ;
Pattern r = Pattern . compile ( pattern ) ;
 
List <String> input = new ArrayList <String> ( ) ;
input . add ( "Crunchify" ) ;
input . add ( "Crunchify123#" ) ;
input . add ( "crunchify123#" ) ;
input . add ( "crunchify** " ) ;
input . add ( "Crunchify123!!" ) ;
 
for ( String password : input ) {
Matcher m = r . matcher ( password ) ;
if ( m . matches ( ) )
System . out . println ( "Password: " + password + " is valid" ) ;
else
System . out . println ( "Password: " + password + " is NOT valid" ) ;
}
 
}
}

结果：

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Password: Crunchify is NOT valid
Password: Crunchify123# is valid
Password: crunchify123# is NOT valid
Password: crunchify**  is NOT valid
Password: Crunchify123!! is valid