HTML 5 应用程序缓存的介绍
http://www.w3school.com.cn/html5/html_5_app_cache.asp
接下来通过实际案例介绍HTML5应用程序缓存的介绍。
一 应用服务器
应用服务器使用tomcat.
在tomcat的web.xml 添加如下配置,因为manifest文件返回时MIME-type必须为 text/cache-manifest
<mime-mapping> <extension>appcache</extension> <mime-type>text/cache-manifest</mime-type> </mime-mapping>
二 页面
manifest文件default.appcache
缓存staticPage.html,不缓存 * 即所有文件。如果页面不存在或无法连接到网路，跳转到errorPage.html
CACHE MANIFEST staticPage.html NETWORK: * FALLBACK:/ errorPage.html
index.html 引入default.appcache 缓存文件
<!DOCTYPE html><html manifest="default.appcache"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> this is the index page!</body></html>
staticPage.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> this is the static page! eee</body></html>
randomPage.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body>This is the random page!</body></html>
errorPage.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> <h1 id="Error-nbsp">Error !!!</h1></body></html>
所有以上html及缓存文件(default.appcache)都在同一目录下。
现在让我们看看测试结果如何.
访问 http://localhost:8080/webapp/index.html
结果如下
从控制台上的信息，可知staticPage.html,errorPage.html已被缓存.
停止服务器。
访问 http://localhost:8080/webapp/staticPage.html 正常。缓存起效
访问 http://localhost:8080/webapp/randomPage.html 返回errorPage.html内容。yes，FALLBACK配置起效.
访问 http://localhost:8080/webapp/index.html 正常. no, 这不是我们想要的，因为我们并没有设置这个页面要缓存。 从w3cshcool介绍中可知 每个指定了 manifest 的页面在用户对其访问时都会被缓存。
有如下一个方案针对以上问题。
添加cachePage.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html manifest="default.appcache"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body></body></html>
修改index.html body内添加如下。
<iframe src="cachePage.html" style="display:none;"></iframe>
经测试，不可行。
summary:
如果应用有A,B,C,D 页面。
A 页面中引入了一个manifest文件，该manifest文件，缓存B文件，C文件作为错误页面。
当请求A页面是，浏览器会缓存A，B,C页面，及manifest文件。
如果A、B、C页面有跟新,要刷新文件，就对服务器端的manifest文件做任意修改(或者删除服务器端的manifest文件, 如果这样当用户访问任意缓存页面时，浏览器会尝试同步manifest文件，发现文件不存在，然后删除所有客户端缓存)。
每次访问A，B，C(缓存页面)，浏览器都会对manifest文件做一次同步。
访问非缓存的文件，则manifest文件不会同步。
也就是说，每次访问缓存文件，浏览器会去同步manifest文件,
如果manifest文件有跟新，则刷新缓存文件列表(更新缓存文件、删除缓存文件、添加缓存文件)。
然后再次访问缓存文件时就可以看到更新的内容了。
以上都在chrome版本41.0.2272.118做测试。
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