ubuntu使用Apache2配置多个站点

我想实现一个IP下承载多个域名的访问的效果
我已经在sites-available/000-default.conf中添加了类似下面的代码，但是每次访问时，总是跳转到我的首选主页中了，请问怎么处理呀？
<VirtualHost *:80>
           ServerAdmin webmaster@localhost
           ServerName xxx.com
           CustomLog   /var/log/apache2/xxx.com-access.log combined
           DocumentRoot /var/www/html/xxx
           <Directory /var/www/html/xxx>
                   Options Indexes FollowSymLinks MultiViews
                   AllowOverride all
                   Order allow,deny
                   allow from all
          </Directory>
</VirtualHost>                  
  <VirtualHost *:80>
           ServerAdmin webmaster@localhost
           ServerName www.xxx.com
           CustomLog   /var/log/apache2/xxx.com-access.log combined
           DocumentRoot /var/www/html/xxx
           <Directory /var/www/html/xxx>
                   Options Indexes FollowSymLinks MultiViews
                   AllowOverride all
                   Order allow,deny
                   allow from all
          </Directory>
</VirtualHost>