Java RegEx – Mask Phone Numbers example shows how to mask phone numbers using regex in Java. It also shows how to mask starting few digits with the * (asterisk) of the phone numbers.
How to mask phone numbers using a regex pattern in Java?
In many use cases, we need to mask the first few digits of a phone number. For example, in many applications, phone numbers are displayed on the front-end with starting few digits marked as * in order to avoid misuse and protect the privacy of the customer.
Masking of phone number digits can be done using a regex pattern. We need to first determine how many digits we need to mask using the asterisk (*). Here is the regex pattern assuming that we want to display the last 3 digits out of 10. The rest of the digits need to be displayed as an *.
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\\d(?=\\d{3}) |
Where,
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\\d - Any digit (?=) - Positive lookahead expression \\d{3} - Any digit 3 times |
The positive lookahead expression looks for the given expression to the right side from the current position. In simple words, it is used when we want to search for something in a string followed by something else but do not want to include that something else in the match.
In the above pattern, we are matching a digit that is followed by exactly 3 digits in the string. For example, in a 10 digit number, it will match from the start of the string till the 7th digit. Because that is the last digit that is followed by 3 more digits.
Once we get that match, we will use the replaceAll method to replace all the matching digits with an asterisk character as given below.
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package com.javacodeexamples.regex; public class RegExMaskPhoneNumbers { public static void main(String[] args) { String[] strPhoneNumbers = { "12344", "0123456789", "911234567890" }; String strPattern = "\\d(?=\\d{3})"; for(String phoneNumber : strPhoneNumbers) { System.out.println( phoneNumber.replaceAll(strPattern, "*") ); } } } |
Output
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**344 *******789 *********890 |
As you can see from the output, regardless of the length of the phone number, it always displays the last 3 digits of it. You can adjust the pattern to display n number of unmasked digits. For example, If you want to display the last 4 digits instead of 3, you can use a pattern like “\\d(?=\\d{4})”.
Important Note:
Before masking the phone number, replace all non-digit characters from the phone numbers like hyphens for the pattern to work properly. You can use “[^0-9]” to replace all non-digit characters. See below given example.
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package com.javacodeexamples.regex; public class RegExMaskPhoneNumbers { public static void main(String[] args) { String[] strPhoneNumbers = { "12344", "012-345-6789", "91-123-456-7890" }; String strPattern = "\\d(?=\\d{3})"; for(String phoneNumber : strPhoneNumbers) { System.out.println( phoneNumber.replaceAll("[^0-9]", "").replaceAll(strPattern, "*") ); } } } |
Output
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**344 *******789 *********890 |
If you want to learn more about the regex patterns, visit the Java RegEx tutorial.
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