Multisite with www prefix, domain mapping

I have multisite wordpress using subdirectory system.

for instance, my site root domain is abcd.com, my wp-config is ..

define('WP_ALLOW_MULTISITE', true); define('MULTISITE',true);
define('SUBDOMAIN_INSTALL',false);
define('DOMAIN_CURRENT_SITE','abcd.com');
define('PATH_CURRENT_SITE','/'); define('SITE_ID_CURRENT_SITE',1);
define('BLOG_ID_CURRENT_SITE',1);

I connect to http://www.abcd.com but browser’s address bar has abcd.com. not http://www.abcd.com

I need www. prefix, so I change DOMAIN_CURRENT_SITE ‘abcd.com’ to ‘www.abcd.com’. but working root page broken all links (connect link -> redirect to root page)

my .httaccess

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

<IfModule mod_url.c>
ServerEncoding UTF-8
ClientEncoding EUC-KR
</IfModule>

And Second problem is domain name too.

first site’s domain name is abcd.com/ , second abcd.com/site2

abcd.com/ using this domain name

and site2 using http://www.site2.com good working all links are working perfectly.

but still link’s url is abcd.com/site2/somthing

I want to change abcd.com/site2/somthing to http://www.site2.com/something

What can I do?