Mod_expires does not affect caching

Probably the ProxyPass / directive you have in your config routes all requests to the Tomcat backend, bypassing all your mod_rewrite directives. You can try to remove the ProxyPass directive and use RewriteRule with the [P] flag after your other rewrites:

• mod_rewrite: P|proxy

For the expire headers the situation is worse — in another similar question a solution was not found.

Option +FollowSymLinks would be needed for using mod_rewrite in .htaccess files; in your case it is not required, because you can put everything in the Apache config. Moving rules from config to .htaccess is pointless and can only make things slower. However, there is an important difference between .htaccess and the Apache config — in .htaccess patterns in RewriteRule are matched against relative filesystem paths (which never start with /), while in the VirtualHost context these patterns are matched against the URL path after the hostname, which always starts with /. Therefore at least one of your rules is incorrect:

RewriteRule ^content/(js|css)/([a-z]+)-([0-9]+)\.(js|css)$ /content/$1/$2.$4

should be

RewriteRule ^/content/(js|css)/([a-z]+)-([0-9]+)\.(js|css)$ /content/$1/$2.$4

(note the additional slash in the beginning).

I went ahead and researched this one out. After reading multiple tutorials and the Apache doc, I was able to piece together something substantial, which seems to work well. Using the list above, I put together a set of rules/declaratives which seem to handle compression with the mainstream content types:

<Location />
# Insert filter
SetOutputFilter DEFLATE

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/x-js text/javascript text/css 
AddOutputFilterByType DEFLATE application/xml application/xhtml+xml application/x-javascript application/javascript
AddOutputFilterByType DEFLATE application/json

BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

# Don't compress images
SetEnvIfNoCase Request_URI \
\.(?:gif|jpe?g|png)$ no-gzip dont-vary

SetEnvIfNoCase Request_URI \
    \.(?:exe|t?gz|zip|bz2|sit|rar)$ \
    no-gzip dont-vary
SetEnvIfNoCase Request_URI \.pdf$ no-gzip dont-vary

</Location>

For testing, I basically used TamperData for Firefox and turned on deflate logging for apache:

https://addons.mozilla.org/en-US/firefox/addon/tamper-data/

For Apache, add the following:

# For Testing Purposes
DeflateFilterNote Input instream
DeflateFilterNote Output outstream
DeflateFilterNote Ratio ratio

#LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
CustomLog logs/deflate_log deflate

http://httpd.apache.org/docs/2.0/mod/mod_deflate.html#deflatefilternote