¿Qué es el patrón RegEx (expresión regular)? ¿Cómo usarlo en Java? Ejemplo adjunto

Publicado: 2021-01-25
¿Qué es el patrón RegEx (expresión regular)? ¿Cómo usarlo en Java?

¿Qué es RegEx?

Regular Expression es un patrón de búsqueda para String. java.util.regex Clases para hacer coincidir secuencias de caracteres con patrones especificados por expresiones regulares en Java.

Podrías usar Regex para:

  • Búsqueda de texto
  • Extrayendo Texto
  • Modificación de texto

Analicemos algunas sintaxis básicas:

Clases de caracteres en Regex:

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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 ]

Cuantificadores en Regex:

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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 también es un ejemplo de Regex.

Metacaracteres en Regex:

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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

Vamos a empezar a trabajar en el ejemplo. En el siguiente ejemplo, repasaremos 5 ejemplos de Regex diff.

  1. Cómo analizar el resultado del comando de tiempo de actividad en Java
  2. Comprobar si la URL termina con una extensión específica
  3. Compruebe si existe una IP válida
  4. Ejemplo de ReplaceAll() de Regex
  5. Averigüe si el SSN es válido
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" ) ;
}
 
}
}

Producción:

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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

¿Cómo validar la seguridad de la contraseña usando el código Java?

Encuentra a continuación mis condiciones:

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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" ) ;
}
 
}
}

Resultado:

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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