Why Doesn't My Java Regex Match Email Addresses?

Java Regex Email Validation

Question

A user has encountered difficulty using a regex for email validation in Java. Despite the regex matching in a "find and replace" operation within Eclipse, it fails to find email addresses using the Java Matcher class.

The user has provided the following regex:

\b[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b

In Java, the code they have written is:

Pattern p = Pattern.compile("\b[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b");
Matcher m = p.matcher("[email protected]");

if (m.find())
    System.out.println("Correct!");

However, the regex fails to match regardless of whether the email is well-formed or not.

Answer

The provided regex is similar to the one used in the given Java code. However, there are a few key differences:

• The provided regex uses character classes with braces, such as [A-Z0-9._%-] . In Java, these should be escaped as [A-Z0-9._%-] .
• The provided regex uses dot as a literal character ., which should be escaped as \. using a double backslash in Java.
• The provided regex uses a special character b to match the beginning of a word, which is not needed for email validation and can be removed.

The following Java code has been modified to address these issues:

Pattern p = Pattern.compile("[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}");
Matcher m = p.matcher("[email protected]");

if (m.find())
    System.out.println("Correct!");

With these modifications, the regex should now match email addresses in Java as expected.

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