How to write a rule in vhost definition file to redirect example.com > www.example.com

I had a rule that redirect example.com > www.example.com. I removed htaccess file and placed rules into a /etc/apache2/sites-available/example virtual host definition file. And basically rule above stopped working.

Here is the code, I would appreciate any help and it would be fun to know why the thing stopped working.

ServerName www.example.com
ServerAlias example.com
DocumentRoot /var/www/symfony/web

<Directory /var/www/symfony/web>
    AllowOverride Non开发者_运维问答e
    Allow from All
    Options FollowSymLinks ExecCGI

    RewriteEngine On

    #RewriteBase /

    RewriteCond %{HTTP_HOST} !^www\.
    RewriteRule ^ http://www.%{HTTP_HOST}%{REQUEST_URI}[L,R=301]

    # we skip all files with .something
    RewriteCond %{REQUEST_URI} \..+$
    RewriteCond %{REQUEST_URI} !\.html$
    RewriteRule .* - [L]

    RewriteRule ^$ index.html [QSA]
    RewriteRule ^([^.]+)$ $1.html [QSA]
    RewriteCond  %{REQUEST_FILENAME} !-f

    RewriteRule ^(.*)$ index.php [QSA,L]
</Directory>

You may want to just use Redirect in apache instead of messing with .htaccess. See my answer to a similar question.