Category Image The Power of Regular Expressions


Regular Expressions (RegEx for short) are a very powerful tool that can save a LOT of lines of code especially when validating input data...

Learning RegEx can be a little daunting, but with the help of a RegEx Explorer/Coach tool, life can be very easy.

For Mac, I recommend RegexPlor (downloadable at MacUpdate ) and for Windows, try the really excellent Regex Coach . Simply build your expression and test it in one of these apps. Then copy/paste the regex into your code and escape all the slashes by replacing every single slash with 2 slashes.

A common use of RegEx in WebObjects java is validating user input using java's matches method of the String class. Alternatively use the Pattern class for better efficiency in repetitive use of the code.

This online tutorial site has dedicated java information too with the most important thing to remember is to escape the RegEx strings that you use as arguments in java.

Since java uses a single slash as an escape character, then all Regex escapes must be double slashes which is an escaped slash!


Here is a simple command line java class for checking email addresses. You can compile it on the command line and run it with an email address argument.
public class EmailRegEx {
public static void main (String args[]) {
String aString = args[0];

String regex = new String(
"^[a-zA-Z0-9\\._%-]+@[a-zA-Z0-9\\._%-]+\\.[a-zA-Z]{2,4}$" );


System.out.println("Regular Expression: " + regex);

if (aString.matches(regex) == true) {
System.out.println("GOOD: " + aString);
} else {
System.out.println("BAD : " + aString);
}

}
}

Another example, here is a validation method for a zip code field:
public static String validateZip(Object aValue) throws
NSValidation.ValidationException {
String errorMessage = "Zip Code must be entered as 99999 or 99999-9999.";

// Regex string: ^\d{5}$|^\d{5}\-\d{4}$
String zipRegex = "^\\d{5}$|^\\d{5}\\-\\d{4}$";
Object theValue;

if (aValue instanceof Number) {
theValue = (Object)((Number)aValue).toString();
} else {
theValue = aValue;
}

if (theValue instanceof String) {
if( ((String)theValue).matches(zipRegex) == true ) {
// we have a valid zip
return (String)theValue;
} else {
throw new NSValidation.ValidationException(errorMessage);
}
} else {
throw new NSValidation.ValidationException(errorMessage);
}
}

Here is a validation for US style phone numbers...
/** Checks that an object is a valid phone number
@param Object aValue
@param field name for constructing error message. Can be null.
@return the valid phone number digits only */
public static String validatePhone(Object aValue, String fieldName) throws
NSValidation.ValidationException {
String errorMessage;
if (fieldName == null) {
errorMessage = "Must be entered as 999-999-9999 or (999) 999-9999 or 9999999999.";
} else {
errorMessage = fieldName + " must be entered as 999-999-9999 or (999) 999-9999 or 9999999999.";
}

String phoneRegex = "^\\(?\\d{3}(\\)?|-?)\\s*\\d{3}-?\\d{4}$";
Object theValue;

if (aValue instanceof Number) {
theValue = (Object)((Number)aValue).toString();
} else {
theValue = aValue;
}

if (theValue instanceof String) {
if( ((String)theValue).matches(phoneRegex) == true ) {
// we have a valid phone number
// strip everything but the digits
return ((String)theValue).replaceAll("\\D","");
} else {
throw new NSValidation.ValidationException(errorMessage);
}
} else {
throw new NSValidation.ValidationException(errorMessage);
}
}


Some other useful Regex...

Checking a login name of between 6 and 32 characters beginning with a letter and allowed to have numbers, letters and these chars @ _ - . $
String loginNameRegex = "^[a-zA-Z][@_\\-\\.\\$\\w]{5,31}$";

Credit Card Security Code. Either 3 or 4 characters
String regex = "^\\d{3}$|^\\d{4}$";

Posted: Tuesday - January 18, 2005 at 05:05 PM        

Published by