What is RegEx?
Regular Expression is a search pattern for String. java.util.regex Classes for matching character sequences against patterns specified by regular expressions in Java.
You could use Regex for:
- Searching Text
- Extrating Text
- Modifying Text
Let’s discuss some basic syntax:
Character Classes in Regex:
. 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]
Quantifiers in Regex:
* 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 also an Regex example.
Meta Characters in Regex:
\ 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
Let’s start working on example. In below example we will go over 5 diff Regex Examples.
- How to Parse uptime command result in Java
- Check if URL ends with specific extension
- Check if valid IP present
- Regex’s ReplaceAll() Example
- Find if SSN is valid
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\\.]+)$");
String output = " 10:17:32 up 189 days, 18:49, 5 user, load average: 2.07, 1.11, 1.16";
Matcher m = uptimePattern.matcher(output);
if (m.matches()) {
final double crunchify1MinuteLoadAvg = Double.parseDouble(m.group(1));
final double crunchify5eMinuteloadAvg = Double.parseDouble(m.group(2));
final double crunchify15MinuteLoadAvg = Double.parseDouble(m.group(3));
System.out.println("Load Average 1 min: " + crunchify1MinuteLoadAvg);
System.out.println("Load Average 5 min: " + crunchify5eMinuteloadAvg);
System.out.println("Load Average 15 min: " + crunchify15MinuteLoadAvg);
} else {
System.out.println("no matches found");
}
}
}
Output:
Load Average 1 min: 2.07 Load Average 5 min: 1.11 Load Average 15 min: 1.16 ========================== URL pattern found ========================== 192.abc.0.1 : false 192.168.0.1 : true ========================== This is Crunchify.com Spring MVC Tutorial. ========================== SSN 123-45-6789 is valid SSN 123-456-789 is NOT valid
How to validate Password strength using Java Code?
Find below my conditions:
# must contains one digit from 0-9
(?=.*[a-z]) must contains one lowercase characters
(?=.*[A-Z]) must contains one uppercase characters
(?=.*[!@#$%]) must contains one special symbols in the list "!@#$%"
. match anything with previous condition checking
{8,25} length at least 8 characters and maximum of 25
CrunchifyPasswordVerification.java
package crunchify.com.tutorial;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* @author Crunchify.com
*
*/
public class CrunchifyPasswordVerification {
public static void main(String[] args) {
String pattern = "((?=.*[@!#$%])(?=.*[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");
}
}
}
Result:
Password: Crunchify is NOT valid Password: Crunchify123# is valid Password: crunchify123# is NOT valid Password: crunchify** is NOT valid Password: Crunchify123!! is valid