找不到对象！ 网址重写

I have rewrited my url's with htaccess and now I the following URL

This is my old URL:

http://example.com/user.php?username=collins1

The new URL:

http://example.com/user/collins1/

The .htaccess file:

Options +FollowSymLinks -MultiViews
# Turn mod_rewrite on
RewriteEngine On
RewriteBase /
RewriteRule ^user\.php$ %{QUERY_STRING} [C]
RewriteRule ^username=(.*) /user/$1/? [R=301,L]

It get an Object not found! response, kindly help

You are redirecting not rewriting your url, for internal rewrite use this

RewriteEngine On RewriteRule ^user/([^/]*)/$ /user.php?username=$1 [L]