无法使用 Java 的 URLConnection 获取响应标头位置

发布于 2024-09-24 10:45:32 字数 282 浏览 2 评论 0原文

有人可以建议我在这里做错了什么吗？
我正在尝试使用 Java 获取某个 URL 的标头位置这是我的代码：

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

这很奇怪，因为我确信我所指的 URL 返回 Location 标头，并且使用 getContentType() 或 getContentLength() 等方法可以完美地工作

原文

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:

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

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誰ツ都不明白 2024-10-01 10:45:32

也许 Location 标头作为重定向响应的一部分返回。如果是这样，URLConnection 通过向指向的资源发出第二个请求来自动处理重定向，因此您需要禁用它：

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

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，则可以调用 getURL() （在建立连接后）。

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:

((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).

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相对绾红妆 2024-10-01 10:45:32

只是对 axtavt 答案进行跟进...如果网址有多个重定向，您可以执行类似的操作，以便获取直接链接：

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;
}

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:

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;
}

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