Android:如何知道位于 Web 服务器中的文件已被修改? [英] Android: how to know file located in web server is modified?
问题描述
我正在解析位于 Web 服务器中的 Xml 文件并将解析后的数据存储到数据库中.对于我的应用程序，我使用的是数据库中的数据.仅当文件被修改时我才需要解析 xml 文件，否则不需要解析.那么我怎么知道文件被修改了呢?我知道我可以使用if-modified-since"标题.但我需要一些if-modified-since"标题的例子
请帮帮我......
I am parsing Xml file located in web server and storing parsed data in to database. for my app I am using data from database. I need to parse the xml file only if the file is modified otherwise no need to parse. So how can I know the file is modified? I know I can use "if-modified-since" header. But
I need some examples of "if-modified-since" header
please help me.......
推荐答案
由于您是从 Web 服务器检索 .xml 文件，因此这应该相对容易，而无需进行服务器端 MD5 求和.
Since you are retrieving your .xml file from a web server, this should be relatively easy without having to do a server side MD5 sum.
如果您对 xml 文件执行 HTTP 请求，您可以简单地从 Web 服务器执行 HEAD 请求，如果文件已更改/修改或不存在，它将返回.这也是轻量级的，最好的部分是服务器应该已经为你做这件事了.
If you are doing a HTTP request for the xml file you can simply perform a HEAD request from the web server and this will return if the file has changed/modified or if it doesn't exist. This is also lightweight and the best part is that the server should already do this for you.
编辑:重新阅读您的问题，看起来您有相同的想法.这是代码.
Edit: re-reading your question, looks like you had the same idea. Here's the code.
import java.net.*;
import java.io.*;
// Using HTTP_NOT_MODIFIED
public static boolean Changed(String url){
try {
HttpURLConnection.setFollowRedirects(false);
HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection();
con.setRequestMethod("HEAD");
return (con.getResponseCode() == HttpURLConnection.HTTP_NOT_MODIFIED);
}
catch (Exception e) {
e.printStackTrace();
return false;
}
}
// GET THE LAST MODIFIED TIME
public static long LastModified(String url)
{
HttpURLConnection.setFollowRedirects(false);
HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection();
long date = con.getLastModified();
if (date == 0)
System.out.println("No last-modified information.");
else
System.out.println("Last-Modified: " + new Date(date));
return date;
}
见:
或者，如果您的服务器支持它们，您可以使用 ETags 来确定您的文件是否已被修改.
Alternatively if your server supports them you can use ETags to find out if your file has been modified.
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