如果使用上述两个<VirtualHost *:80>块的解决方案，具有不同的ServerNames…

<VirtualHost *:80>
    ServerName example.com
    Redirect permanent / http://www.example.com/
</VirtualHost>
<VirtualHost *:80>
    ServerName www.example.com
</VirtualHost>

．.． 那么你必须设置NameVirtualHost On。

如果你不这样做，Apache不允许自己使用不同的servername来区分块，所以你会得到这个错误消息:

[warn] _default_ VirtualHost overlap on port 80, the first has precedence

…或者没有重定向发生，或者有一个无限重定向循环，这取决于你先放哪个块。

http://example.com/subdir/?lold=13666 => http://www.example.com/subdir/?lold=13666

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

这很简单!

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

如果你正在使用Apache 2.4，不需要启用重写Apache模块，你可以使用这样的东西:

# non-www to www
<If "%{HTTP_HOST} = 'domain.com'">
  Redirect 301 "/" "http://www.domain.com/"
</If>

要将所有直接发送到域名www的请求重定向到301，您可以使用:

RewriteEngine On

RewriteCond %{HTTP_HOST} !^([^.]+\.[^.]+){2,}$ [NC]
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

这样做的好处是，如果你有任何有效的子域，这将工作。

example.com重定向到www.example.com

没有重定向

没有重定向

RewriteCond %{HTTP_HOST} ^!example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]

This starts with the HTTP_HOST variable, which contains just the domain name portion of the incoming URL (example.com). Assuming the domain name does not contain a www. and matches your domain name exactly, then the RewriteRule comes into play. The pattern ^(.*)$ will match everything in the REQUEST_URI, which is the resource requested in the HTTP request (foo/blah/index.html). It stores this in a back reference, which is then used to rewrite the URL with the new domain name (one that starts with www).

[NC]表示不区分大小写的模式匹配，[R=301]表示使用代码301进行外部重定向(资源永久移动)，[L]停止所有进一步重写，并立即重定向。