some Java Test

public static bool isUsernameValid(string username) {
    RegEx r = new Regex(“^[A-Za-z0-9]{16}$”);
    return r.isMatch(username); 
}

// java.sql.Connection conn is set elsewhere for brevity.
PreparedStatement ps = null;
RecordSet rs = null;
try {
    pUserName = request.getParameter(“UserName”);
    if ( isUsernameValid (pUsername);
        ps = conn.prepareStatement(“SELECT * FROM user_table 
                                   WHERE username = ? ”);
        ps.setString(1, pUsername);
        rs = ps.execute();
        if ( rs.next() ) {
            // do the work of making the user record active in some way
        }
    } else { // handle invalid input }
}
catch (…) { // handle all exceptions … }