Request Headers:

response headers go from the server to the browser and request headers go from the browser to the server.

Read this thread for better understanding.

Here is a link that talks about sending data back to the client.

Retrieving a parameter from a link

Check it here

HttpServlet.getLastModified() method purpose and usage.

Check it here

The two most significant filters that every web application should have.

Compression and Caching Filters