如何实现httpclient的HEAD方法
您好，我正在从服务器下载文件。我必须使用 HEAD 方法获取元信息。 andybody 帮助我实现 HEAD 方法来获取“上次修改”日期和修改日期。
这是我的代码：
HttpClient client= new DefaultHttpClient();
//HttpGet get = new HttpGet(url);
HttpHead method = new HttpHead(url);
HttpResponse response= client.execute(method);
Header[] s=response.getAllHeaders();
System.out.println("THe header from the httpclient:");
for(int i=0; i < s.length; i++){
Header hd = s[i];
System.out.println("Header Name: "+hd.getName()
+ " " + " Header Value: " + hd.getValue());
}
//here I have to implement the HEAD method
Hi I am downloading file from server. I have to take meta-information using HEAD method. andybody help me to implement the HEAD method to get "last-modified" date and modified-since date.
here is my code:
HttpClient client= new DefaultHttpClient();
//HttpGet get = new HttpGet(url);
HttpHead method = new HttpHead(url);
HttpResponse response= client.execute(method);
Header[] s=response.getAllHeaders();
System.out.println("THe header from the httpclient:");
for(int i=0; i < s.length; i++){
Header hd = s[i];
System.out.println("Header Name: "+hd.getName()
+ " " + " Header Value: " + hd.getValue());
}
//here I have to implement the HEAD method
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HEAD 和 GET 方法之间的区别在于响应不包含正文。否则，两者是相同的。换句话说，HEAD 方法获取所有标头。它不用于获取单个标头的数据，它只是一次检索所有标头。
在代码示例中，您已经拥有所有标头，因为您执行了 HEAD 请求。在 for 循环中，您输出标头中的所有数据。如果
last-modified不存在，则服务器没有为此资源提供它。请注意，
if-modified-since是请求标头字段，而不是响应标头字段。您可以将其设置为指示服务器仅在修改日期已过时才返回资源。如果您打算仅在服务器上修改资源时检索该资源，则可以仅使用带有if-modified-since标头集的 GET 请求。要了解服务器是否支持此标头，请检查此工具： http://www.feedthebot.com /工具/如果修改/The difference between a HEAD and a GET method is that the response will not contain a body. Otherwise, the two are the same. In other words, a HEAD method gets all the headers. It is not used for getting data of a single header, it just retrieves all headers at once.
In the code example you already have all headers, because you executed a HEAD request. In the for-loop you output all data from the headers. If the
last-modifiedis not there, the server did not provide it for this resource.Note that the
if-modified-sinceis a request header field, not a response header field. You can set it to instruct the server to only return the resource if the modified-since date has passed. If you intend to only retrieve a resource when it has been modified on the server, you can just use a GET request with theif-modified-sinceheader set. To know whether a server supports this header, check this tool: http://www.feedthebot.com/tools/if-modified/