How can a string be validated in Java?

Question

How can a string be validated in Java? I.e. only characters are allowed and not numbers? How about email validation?

Answer 1

for string with only characters try

private boolean verifyLastName(String lname)
{
    lname = lname.trim();

    if(lname == null || lname.equals(""))
        return false;

    if(!lname.matches("[a-zA-Z]*"))
        return false;

    return true;
}

for email validation try

private boolean verifyEmail(String email)
{
    email = email.trim();

    if(email == null || email.equals(""))
        return false;

    if(!email.matches("^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,6}$"))
        return false;

    return true;
}

Answer 2

how a string can be validated in java?

A common way to do that is by using a regex, or Regular Expression. In Java you can use the String.matches(String regex) method. With regexes we say you match a string against a pattern If a match is successful, .matches() returns true.

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only characters allowed and not numbers?

// You can use this pattern:
String regex = "^[a-zA-Z]+$";
if (str.matches(regex)) { 
    // ...
}

email validation?

Email addresses have a very complicated spec, which requires a monstrous regex to be accurate. This one is decent and short, but not exactly right:

String regex = "\\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}\\b";
if (str.matches(regex)) { 
    // ...
}

If you really want to look into it: How to validate email and Comparing email validating regexes (PHP).

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Here's an excellent resource to get started on regex:
http://www.regular-expressions.info

Answer 3

For simple cases like that, go with RegExp as NullUserException already suggested. If you need more robust solution you can use some validation framework, i.e. Apache Commons Validator.

Answer 4

If you have Apache commons-lang as a project dependency (and that is quite usual), you can use StringUtils.isAlpha(). If you have a more specific validation or do not want a dependency on commons-lang, you can do it with regular expressions and String.matches().