不能使用Java的URLConnection获得响应头位置

can someone kindly suggest what I'm doing wrong here?
I'm trying to get the header location for a certain URL using Java here is my code:

有人能告诉我我在这里做错了什么吗?我想用Java获取某个URL的头位置，这是我的代码:

URLConnection conn = url.openConnection();
String location = conn.getHeaderField("Location");

it's strange since I know for sure the URL i'm refering to return a Location header and using methods like getContentType() or getContentLength() works perfectly

这很奇怪，因为我确信我所引用的URL返回一个位置头，并使用getContentType()或getContentLength()等方法完美地工作

your advice is much appreciated as always :)

一如既往地感谢您的建议。

Thanks

谢谢

2 个解决方案

#1

Perhaps Location header is returned as a part of redirect response. If so, URLConnection handles redirect automatically by issuing the second request to the pointed resource, so you need to disable it:

可能位置标头作为重定向响应的一部分返回。如果是，URLConnection通过向指定的资源发出第二个请求来自动处理重定向，因此需要禁用它:

((HttpURLConnection) conn).setInstanceFollowRedirects(false);

EDIT: If you actually need a URL of the redirect target and don't want to disable redirect handling, you may call getURL() instead (after connection is established).

编辑:如果您确实需要重定向目标的URL，并且不想禁用重定向处理，您可以调用getURL()(在建立连接之后)。

#2

Just a follow up to axtavt's answer... If the url has multiple redirects, you could do something like this in order to obtain the direct link:

接下来是axtavt的答案……如果url有多个重定向，您可以这样做，以获得直接链接:

String location = "http://www.example.com/download.php?getFile=1";
HttpURLConnection connection = null;
for (;;) {
    URL url = new URL(location);
    connection = (HttpURLConnection) url.openConnection();
    connection.setInstanceFollowRedirects(false);
    String redirectLocation = connection.getHeaderField("Location");
    if (redirectLocation == null) break;
    location = redirectLocation;
}

#1