Delegate specific URL request to specific Directory - apache

Question

Taking forward from my last question i.e. Mapping domains to Tomcat Apps. Now I want that if a particular request came i.e.
http://www.app1.com/blog
then this would be redirected to a specific folder on my server. I did tried below code
Options +FollowSymLinks
RewriteEngine On
RewriteRule ^/blog/ /path_to_my_site/app1_com/blog/ [L]
but that has gone horribly wrong as that has become redirect loop, so I removed it immediately.
Note: My site www.app1.com is hosting java application and www.app1.com/blog would be php application blog.
Update 1
for the sake of clarity below is my virtual host configuration
<virtualhost *:80>
ServerName app1.com
ServerAlias app1.com www.app1.com
Options +FollowSymLinks
RewriteEngine On
RewriteRule ^blog(/.*)?$ /path_to_my_site/blog/ [L,NC]
ProxyPass / ajp://127.0.0.1:8009/app1/
ProxyPassReverse / ajp://127.0.0.1:8009/app1/
</virtualhost>
Update 2
contents of .htaccess in blog folder is
# Pretty Permalinks
RewriteRule ^(images)($|/) - [L]
RewriteCond %{REQUEST_URI} !^action=logout [NC]
RewriteCond %{REQUEST_URI} !^action=login [NC]
Options +FollowSymLinks -MultiViews
RewriteEngine on
RewriteBase /blog/
RewriteCond %{REQUEST_URI} !index\.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?filename=$1 [NC,QSA,L]

Answer 1

You can use:
Options +FollowSymLinks
RewriteEngine On
RewriteRule ^blog(/.*)?$ /path_to_my_site/app1_com/blog/ [L,NC]
/path_to_my_site/app1_com/blog/ should be a valid path under DocumentRoot.
Change your ProxyPass line to this:
ProxyPass /blog !
ProxyPassMatch ^/(?!blog).*$ ajp://127.0.0.1:8009/app1/
ProxyPassReverse / ajp://127.0.0.1:8009/app1/