EDIT It has already been pointed out by several readers that this expression doesn't handle a number of common cases. See the comments or the original blog entry for an updated version.

Recently I needed to create a regular expression to validate the format of a comma-separated list of email addresses. Just thought I’d share the result in case it is of use to anyone:

\w+@\w+\.\w+(,\s*\w+@\w+\.\w+)*

Here’s an example of applying the pattern in Java:

// Compile pattern
Pattern emailAddressPattern = Pattern.compile(String.format("%1$s(,\\s*%1$s)*", "\\w+@\\w+\\.\\w+"));

// Validate addresses
System.out.println(emailAddressPattern.matcher("xyz").matches()); // false
System.out.println(emailAddressPattern.matcher("foo@bar.com").matches()); // true
System.out.println(emailAddressPattern.matcher("foo@bar.com, xyz").matches()); // false
System.out.println(emailAddressPattern.matcher("foo@bar.com, foo@bar.com").matches()); // true