网页的图片是 调用服务器action,以数据流的形式写到页面的。
每次进入页面都会重新下载图片
有没有办法可以缓存图片,在缓存中直接取出
回复讨论(解决方案)
http://www.cnblogs.com/yuyii/archive/2008/10/16/1312238.html
设置Cache-Control
我加上
还是会 去加载图片
图片是个action请求
二进流还能缓存吗?没听说过。页面级缓存都是针对特定资源(xx.扩展名)
这个缓存是在 服务器端实现的 在服务器写出图片留的时候response 增加Last-Modified的参数值,这样浏览器就会将数据缓存起来,当页面再次请求该url的时候请求参数就会带着if-modified-since参数信息,然后判断该参数信息,返回浏览器告知使用缓存数据
下面是部分代码。
//获取缓存文件最后的修改时间(只有缓存过的文件在请求时存在该参数)
String lastUpdateTime = ServletActionContext.getRequest().getHeader("if-modified-since");
//如果存在参数,告知浏览器使用缓存数据
if(lastUpdateTime!=null){
//如果需要判断过期时间,则将文件的最后修改时间与当前时间作比较进行判断
//status:304,使用缓存数据
ServletActionContext.getResponse().setStatus(HttpServletResponse.SC_NOT_MODIFIED);
return null;
}
HttpServletResponse response=ServletActionContext.getResponse();
is = new BufferedInputStream(new FileInputStream(file),1024*1024);
response.setContentType("application/x-download"); // 设置返回的文件类型
response.addHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(uploadFile.getSaveFileName(), "UTF-8"));
//设计缓存为私有缓存,不在用户之间共享
response.setHeader("Cache-Control", "private");
//重要!,浏览器在response中发现该字段,才会将数据存入缓存中,(标记最后修改时间)
response.setDateHeader("Last-Modified",new Date().getTime());

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