实施这一方法将节省你难以置信数额的带宽，极大地加快你的网站为你的网站访客。基本上，对于图片，CSS ， JavaScript以及其他文件可以通过优化更快的下载，告诉你的网站访问者快取记忆体，为他们在某一段时间内。默认的行为是每一次请求检查文件的last-modified 和/或者  Etag headers。

所以一个用户去/home/index.html，及浏览器缓存所有图象和文件。然后用户离开网站稍后回来，与浏览器发送If-Modified-Since 有条件的GET 请求为每一个缓存的项目时，基本上看，如果文件已被改变和他们必须更新他们的缓存。

当你执行在这篇文章中所述的缓存方法，你可以指定某文件或扩展名被缓存为某一特定数额的时间。这些文件然后缓存在你的网站访客和他们不发送If-Modified-Since头直到设置的缓存时间已经到了。

#================================================= ============================#
# TIME CHEAT SHEET
#================================================= ============================#
# 300 5 M # 604800 1 W
# 2700 45 M # 1814400 3 W
# 3600 1 H # 2419200 1 M
# 54000 15 H # 14515200 6 M
# 86400 1 D # 26611200 11 M
# 518400 6 D # 29030400 1 Y (never expire)

第一个解决办法是Apache模块mod_expires 1.3 2.0 2.2

ExpiresActive On
ExpiresDefault A300
ExpiresByType image/x-icon A2592000
ExpiresByType application/x-javascript A2592000
ExpiresByType text/css A2592000
ExpiresByType image/gif A604800
ExpiresByType image/png A604800
ExpiresByType image/jpeg A604800
ExpiresByType text/plain A604800
ExpiresByType application/x-shockwave-flash A604800
ExpiresByType video/x-flv A604800
ExpiresByType application/pdf A604800
ExpiresByType text/html A300

第二个解决办法是mod_headers 1.3 2.0 2.2

# YEAR
<FilesMatch “\.(flv|gif|ico)$”>
Header set Cache-Control “max-age=2592000”
</FilesMatch>

# WEEK
<FilesMatch “\.(pdf|swf|js|css)$”>
Header set Cache-Control “max-age=604800”
</FilesMatch>

# NEVER CACHE
<FilesMatch “\.(html|cgi|php|htm)$”>
Header set Expires “Thu, 01 Dec 2003 16:00:00 GMT”
Header set Cache-Control “no-store, no-cache, must-revalidate”
Header set Pragma “no-cache”
</FilesMatch>

注：用filesmatch和files在htaccess文件

这里是Headers当下载一个JPEG图像的时候，

这个缓存方案实施后和没有缓存时的效果。

JPEG 没有缓存的时
Last-Modified: Wed, 22 Feb 2006 12:16:56 GMT
ETag: “b57d54-45e7”
Accept-Ranges: bytes
Content-Length: 17895
Connection: close
Content-Type: image/jpeg
缓存过的
Cache-Control: max-age=2592000
Expires: Tue, 28 Mar 2006 16:23:52 GMT
Last-Modified: Wed, 22 Feb 2006 12:16:56 GMT
ETag: “b57d54”
Accept-Ranges: bytes
Content-Length: 17895
Connection: close
Content-Type: image/jpeg
Content-Language: en

附：

apache配置文件例子：

example 1

# htm files are php
AddHandler application/x-httpd-php .php .htm

# setup errordocuments to local php file
ErrorDocument 404 /cgi-bin/error.htm
ErrorDocument 403 /cgi-bin/error.htm
ErrorDocument 500 /cgi-bin/error.htm

# Turn on Expires and set default expires to 3 days
ExpiresActive On
ExpiresDefault A259200

# Set up caching on media files for 1 month
<FilesMatch “\.(ico|gif|jpg|jpeg|png|flv|pdf|swf|mov|mp3|wmv|pp t)$”>
ExpiresDefault A2419200
Header append Cache-Control “public”
</FilesMatch>

# Set up 2 Hour caching on commonly updated files
<FilesMatch “\.(xml|txt|html|js|css)$”>
ExpiresDefault A7200
Header append Cache-Control “private, must-revalidate”
</FilesMatch>

# Force no caching for dynamic files
<FilesMatch “\.(php|cgi|pl|htm)$”>
ExpiresDefault A0
Header set Cache-Control “no-store, no-cache, must-revalidate, max-age=0”
Header set Pragma “no-cache”
</FilesMatch>

example 2

# htm files are php
AddHandler application/x-httpd-php .php .htm

# setup errordocuments to local php file
ErrorDocument 404 /cgi-bin/error.htm
ErrorDocument 403 /cgi-bin/error.htm
ErrorDocument 500 /cgi-bin/error.htm

# Turn on Expires and set default to 0
ExpiresActive On
ExpiresDefault A0

# Set up caching on media files for 1 year (forever?)
<FilesMatch “\.(ico|flv|pdf|mov|mp3|wmv|ppt)$”>
ExpiresDefault A29030400
Header append Cache-Control “public”
</FilesMatch>

# Set up caching on media files for 1 week
<FilesMatch “\.(gif|jpg|jpeg|png|swf)$”>
ExpiresDefault A604800
Header append Cache-Control “public, proxy-revalidate”
</FilesMatch>

# Set up 2 Hour caching on commonly updated files
<FilesMatch “\.(xml|txt|html|js|css)$”>
ExpiresDefault A7200
Header append Cache-Control “private, proxy-revalidate, must-revalidate”
</FilesMatch>

# Force no caching for dynamic files
<FilesMatch “\.(php|cgi|pl|htm)$”>
ExpiresDefault A0
Header set Cache-Control “no-cache, no-store, must-revalidate, max-age=0, proxy-revalidate, no-transform”
Header set Pragma “no-cache”
</FilesMatch>

-end-

原始文章: Speed Up Sites with htaccess Caching (http://www.askapache.com/htaccess/speed-up-sites-with-htaccess-caching.html)