How To Redirect Non www To www in .htaccess

Step 1. Enable mod_rewrite on your Apache web server.

Step 2. Create .htaccess file in root directory.

Step 3. Redirect Non www To www
    <IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteCond %{HTTP_HOST} !^www\. [NC]
        RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
    </IfModule>

Step 4. Restart Apache Server  
        sudo service apache2 restart