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Che cos'è il modello RegEx (espressione regolare)? Come usarlo in Java? Esempio allegato

Pubblicato: 2021-01-25
Che cos'è il modello RegEx (espressione regolare)? Come usarlo in Java?

Cos'è RegEx?

Regular Expression è un modello di ricerca per String. java.util.regex Classi per la corrispondenza di sequenze di caratteri con modelli specificati da espressioni regolari in Java.

Puoi usare Regex per:

  • Ricerca di testo
  • Estrazione del testo
  • Modifica del testo

Discutiamo di alcune sintassi di base:

Classi di caratteri in 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 ]

Quantificatori in 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 anche un esempio Regex.

Meta caratteri in 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

Iniziamo a lavorare sull'esempio. Nell'esempio seguente andremo oltre 5 esempi di Regex diff.

  1. Come analizzare il risultato del comando uptime in Java
  2. Controlla se l'URL termina con un'estensione specifica
  3. Controlla se è presente un IP valido
  4. Esempio di ReplaceAll() di Regex
  5. Scopri se SSN è valido
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" ) ;
}
 
}
}

Produzione:

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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

Come convalidare la sicurezza della password utilizzando il codice Java?

Trova sotto le mie condizioni:

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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" ) ;
}
 
}
}

Risultato:

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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