Apache Redirect Request From Domain + Path - apache

Question

I am using apache in front of tomcat so I can redirect requests from the domain to the tomcat url using mod_proxy. I've run into an issue on the server where when using a subdomain it wants to go back to the base domain. Is there any way to redirect all requests from example.com/foo to foo.example.com?
<VirtualHost *:80>
ServerName example.com/app
ProxyPreserveHost Off
ProxyPass / http://app.example.com:8080/AppName/
ProxyPassReverse / http://app.example.com:8080/AppName/
</VirtualHost>
The example above is not working. I presume that is because I cannot include a path in the servername.
Here is my working version of the tag based on the accepted answer.
<VirtualHost *:80>
ServerName example.com/app
ProxyPreserveHost Off
ProxyPass / http://app.example.com:8080/AppName/
ProxyPassReverse / http://app.example.com:8080/AppName/
# Rewrite all request from example.com/foo to foo.example.com
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^/foo/?(.*) http://foo.example.com/$1 [R,L]
</VirtualHost>

Answer 1

Speaking strictly to the last statement in your original post, "Is there any way to redirect all requests from example.com/foo to foo.example.com".
You can use a rewrite to accomplish this. For example:
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^/foo/?(.*) http://foo.example.com/$1 [R,L]
This assumes that your rewrite module is loaded and enabled:
LoadModule rewrite_module modules/mod_rewrite.so
RewriteEngine On

Answer 2

You could use mod_rewrite within apache. Ensure it is enabled, as root:
a2enmod rewrite
That will confirm it is has been enabled or already is. If it has been enabled you'll need a restart of Apache.
Then in your root of your virtualhost create/edit .htaccess file and add the line:
Redirect /foo/ http://foo.example.com/
Depending on your specific directory permissions you may need to allow overrides for the directory
<Directory /your/path/here>
AllowOverride All
</Directory>
HTH