Using Regular Expressions in Java for Data Validation Evelyn Brannock Jan 30, 2009

Definition  They are usually used to give a concise description of a set, without having to list all elements  A regular expression is an expression that describes a set of strings

Origin  In the 1950s, mathematician Stephen Cole Kleene devised a way to describe and classify formal languages using his mathematical notation called regular sets

Using Regular Expressions for Data Validation

Regular Expressions ConstructMatches xThe character x [abc]a, b, or c (simple class) [^abc]Any character except a, b, or c (negation) [a-zA-Z]a through z or A through Z, inclusive (range) \dA digit: [0-9] \DA non-digit: [^0-9] \sA whitespace character \SA non-whitespace character: [^\s] \wA word character: [a-zA-Z_0-9] \WA non-word character: [^\w] *from the Sun Java API

Regular Expressions ConstructMatches X?X?X, once or not at all X*X*X, zero or more times X+X+X, one or more times X{n}X{n}X, exactly n times X{n,}X, at least n times X{n,m}X{n,m}X, at least n but not more than m times XYX followed by Y X|YX|YEither X or Y *from the Sun Java API

Examples  Searching for a word  Matching an address  Verifying the format of a telephone number  Credit card pre-validation  IP address determination  Zip code format validation The regular expression built is determined by the definition of valid values for the field

Building a Regular Expression **Matching a Word**  Words that start with t, with at least one additional letter, all lowercase  t[a-z]+  What if the word can start with a lowercase or uppercase t?  [t|T][a-z]+  What if no additional letters must follow (but they may)?

Building a Regular Expression **Validating and IP Address**  What does an IP address look like?  Are three digits required?  Is a valid IP?  25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?

Steps  Whitespace will often need to be stripped  Determine the valid values of the string  Create the regular expression  Compile the regular expression into a pattern  Place the string you wish to validate into the Matcher class  Does the string match the pattern?

Java Invocation Sequence Two Java classes required: import java.util.regex.Pattern; import java.util.regex.Matcher; Code: Pattern p = Pattern.compile("a*b"); Matcher m = p.matcher("aaaaab"); boolean b = m.matches();compilematchermatches

U.S. Zip Code  What is a valid expression for a zip code?  Let’s build the regular expression together using GGCCustomerZipCode.java

Further Reading  Teach Yourself Regular Expressions in 10 Minutes by Ben Forta Teach Yourself Regular Expressions in 10 Minutes by Ben Forta  Mastering Regular Expressions by Jeffrey Friedl Mastering Regular Expressions by Jeffrey Friedl  Java Regular Expressions by Mehran Habibi Java Regular Expressions by Mehran Habibi  Regular Expression Pocket Reference by Tony Stubblebine Regular Expression Pocket Reference by Tony Stubblebine  Regular Expression Recipes by Nathan Good Regular Expression Recipes by Nathan Good

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