Does the browser always request a cached file?

Does browser always request a cached file on 开发者_运维知识库each request? (e.g., a CSS style sheet or .js javascript file that has been sent previously)

I'm not sure but i think the answer is "no, it does not".

But then why does the Apache log show that the cached file was requested again? What is the default behavior ?

It really depends on how the page is coded, for example, one can force a web browser to request a script from the web server rather than using its cached copy. So, in short, its not "always" that browser requests scripts from the cache but, "most of the time" it uses cached copy.