Java 電子郵件驗證

Java Email Validation is done to check the accuracy and quality of the email address that the user input. In Java, Email Validation is done with the help of regex expressions. In order to restrict the users to fill the database from the unnecessary email addresses and prevent the application to be used only by authentic users, email addresses play an important role. Almost all the websites and Apps use the email address of the user to sign up and validate them using their algorithms. So before designing the Sign-up Page or performing any task that requires an email address, it is important to validate those email addresses before proceeding further.

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How does email Validation work in Java?

Let us understand the step by step procedure of validating an email in Java along with its implementation in the code:

1. In Java, we validate the email address with the help of the regex expressions.
2. Regular expression is not a language but it defines a pattern for a String through which we can search, compare, edit or manipulate a text. It does not change from language to language (though they are slightly different in some languages).
3. In Java, Regex class is present in the Java library named as java. util.regex
4. In Java, there is a class with the name ‘Pattern’ whose object is the compiled version of the regular expression. In order to create the pattern object, we use its method ‘compile’ (which is public static) and pass the regular expression in it.
5. ‘Matcher’ is a java regex engine object which matches the input string with the object of the Pattern class created above. Method ‘matcher’ takes the input string (email that needs to be checked) as an argument.
6. Method ‘matches’ is used that compares the input string with the regex expression and returns the boolean result based on the decision whether the input string matches with the mentioned regular expression or not.
7. Result is stored in a boolean variable and based on that, the respective message is printed on the console to the user.

We can implement as many restrictions in the validation code of email as we want to depend on the requirement of the application but the general restriction that should be there in the Email address of any user is given below:

• Restriction on ‘@’ part of the email address.
• Restriction on the dots (.) present in the email address whether leading, trailing, or consecutive.
• Restriction on username part of the email address
• Restriction on the no. of characters in the top-level domain name of the email address.

Examples of Java Email Validation

In this article, we would implement all the above-mentioned Validation restrictions and that too step by step to make you understand the code better.

1. Regex to validate the email with ‘@’ in between

There should be one ‘@’ sign present in the email address

import java.util.regex.*;
import java.util.*;
public class Main{
public static boolean isValid(String email)
{
String regex = "^(.+)@(.+)$";
Pattern pattern = Pattern.compile(regex);
if (email == null)
return false;
return pattern.matcher(email).matches();
}
public static void main(String args[]){
String email = "[email protected]";
boolean result = isValid(email);
if (result == true)
System.out.println("Provided email address "+ email+ " is valid \n");
else
System.out.println("Provided email address "+ email+ " is invalid \n");
}
}

Output:

For the below line

address = 'yashi..goyalyahoo.com'

Output:

2. Adding the restriction on the Username part of the email address

• All the capital alphabets [A- Z] are allowed.
• All the small alphabets [a- z] are allowed.
• All the numbers [0- 9] are allowed.
• Email can address can contain dot (.), underscore ( _ ), dash ( – ) in the username.
• Other special characters are not allowed.

import java.util.regex.*;
import java.util.*;
public class Main{
public static boolean isValid(String email)
{
String regex = "^[A-Za-z0-9+_.-]+@(.+)$";
Pattern pattern = Pattern.compile(regex);
if (email == null)
return false;
return pattern.matcher(email).matches();
}
public static void main(String args[]){
String email = "yashi + [email protected]";
boolean result = isValid(email);
if (result == true)
System.out.println("Provided email address "+ email+ " is valid \n");
else
System.out.println("Provided email address "+ email+ " is invalid \n");
}
}

Output:

For the below line

address = '[email protected]'

Output:

3. Restricting email from the dots whether leading, consecutive, or trailing

• More than one dot (.) can be present in the email address
• Consecutive dots are not allowed in both the local and domain part.
• No email is allowed to start or end with a dot.

import java.util.regex.*;
import java.util.*;
public class Main{
public static boolean isValid(String email)
{
String regex = "^[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+(?:\\.[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+)*@[a-zA-Z0-9-]+(?:\\.[a-zA-Z0-9-]+)*$";
Pattern pattern = Pattern.compile(regex);
if (email == null)
return false;
return pattern.matcher(email).matches();
}
public static void main(String args[]){
String email = "[email protected]";
boolean result = isValid(email);
if (result == true)
System.out.println("Provided email address "+ email+ " is valid \n");
else
System.out.println("Provided email address "+ email+ " is invalid \n");
}
}

Output:

For the below line

address = '[email protected]'

Output:

4. Restriction on the number of characters in the domain name

• There should be at least one dot in the domain name.
• In the domain name, after the dot, only the letters would continue.
• Length of domain name should be between 2- 6 letters.

import java.util.regex.*;
import java.util.*;
public class Main{
public static boolean isValid(String email)
{
String regex = "^[\\w!#$%&'*+/=?`{|}~^-]+(?:\\.[\\w!#$%&'*+/=?`{|}~^-]+)*@(?:[a-zA-Z0-9-]+\\.)+[\\a-zA-Z]{2,6}";
Pattern pattern = Pattern.compile(regex);
if (email == null)
return false;
return pattern.matcher(email).matches();
}
public static void main(String args[]){
String email = "[email protected]";
boolean result = isValid(email);
if (result == true)
System.out.println("Provided email address "+ email+ " is valid \n");
else
System.out.println("Provided email address "+ email+ " is invalid \n");
}
}

Output:

For the below line

address = '[email protected]'

Output:

Conclusion

The above description clearly explains what email validation is and how it works in the Java program. Email validation is used widely as it can be a login id or unique username of every user to log in to the website. So it is important for a programmer to learn to validate it before using it for further process in the correct flow of code.

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