java regex match for alphanumeric string

Question

I am trying to check whether a password is alphanumeric or not using regex but I am not getting the result I expect. What is the problem with the below code?

boolean passwordOnlyAlphaNumericCheck = false;
Pattern patternAlphaNumericCheck = Pattern.compile("^[a-zA-Z0-9]$");
Matcher matcherAlphaNumericCheck = patternAlphaNumericCheck.matcher(login.getPassword());
if(matcherAlphaNumericCheck.find())
  passwordOnlyAlphaNumericCheck = true;

Thanks for help

Answer 1

You need to add a quantifier that suits your requirements: * - 0 or more occurrences or + - 1 or more occurrences. You can also omit the ^ and $ and use String.matches() :

boolean passwordOnlyAlphaNumericCheck = false;
if(login.getPassword().matches("[a-zA-Z0-9]*"))
  passwordOnlyAlphaNumericCheck = true;

To match all Unicode letters, use \\p{L} class (and perhaps, \\p{M} to match diacritics): "[\\\\p{L}\\\\p{M}0-9]+" .

what is the difference between login.getPassword().matches("[0-9a-zA-Z]*"); and login.getPassword().matches("[0-9a-zA-Z]"); ?

The .matches("[0-9a-zA-Z]") will only return true if the whole string contains just 1 digit or letter . The * in [0-9a-zA-Z]* will allow an empty string, or a string having zero or more letters/digits.

Answer 2

use this regex expression Take a Demo Here For Regex

"^[a-zA-Z0-9]*$ " Or "^[a-zA-Z0-9]+$"

instead of

"^[a-zA-Z0-9]$ // * or + should be added at last 

So, This might work to you

Pattern patternAlphaNumericCheck = Pattern.compile("^[a-zA-Z0-9]*$");

OR

Pattern patternAlphaNumericCheck = Pattern.compile("^[a-zA-Z0-9]+$");

Answer 3

Your pattern will only match strings with one alphanumeric character, since you have no quantifier and match explicitly from start ( ^ ) to end ( $ ).

Append + for 1+ matches, or * for 0+ matches to your character class.

You can also use the script: \\\\p{Alnum} instead of a tedious character class.

For instance:

• ^\\\\p{Alnum}{8}$ will match a String made of 8 alphanumeric characters
• ^\\\\p{Alnum}{8,}$ will match a String made of 8 or more alphanumeric characters
• ^\\\\p{Alnum}{8,10}$ will match a String made of 8 to 10 alphanumeric characters
• ^\\\\p{Alnum}+$ will match a String made of 1 or more alnums
• ^\\\\p{Alnum}*$ will match an empty String or a String made of any number of alnums

Answer 4

Try this regexp:

private final String nonAlphanumericRegex = ".*\\W.*";
if (Pattern.matches(nonAlphanumericRegex, YOUR_STRING))
    throw IllegalArgumentException()

Answer 5

This function will help ensure that you have just alphanumeric as wanted.

public static boolean isAlphanumeric(String value){
    if (isValueEmpty(value)) {
        return false;
    }

    return value.matches("^[a-zA-Z_0-9]*$");
}

public static boolean isValueEmpty(String param){
    return param == null || param.isEmpty();
}