問題：
I can't understand why Java's HttpURLConnection does not follow an HTTP redirect from an HTTP to an HTTPS URL. 我不明白爲什麼Java的HttpURLConnection不遵循從HTTP到HTTPS URL的HTTP重定向。 I use the following code to get the page at https://httpstat.us/ : 我使用以下代碼在https://httpstat.us/上獲取頁面：
import java.net.URL;
import java.net.HttpURLConnection;
import java.io.InputStream;
public class Tester {
public static void main(String argv[]) throws Exception{
InputStream is = null;
try {
String httpUrl = "http://httpstat.us/301";
URL resourceUrl = new URL(httpUrl);
HttpURLConnection conn = (HttpURLConnection)resourceUrl.openConnection();
conn.setConnectTimeout(15000);
conn.setReadTimeout(15000);
conn.connect();
is = conn.getInputStream();
System.out.println("Original URL: "+httpUrl);
System.out.println("Connected to: "+conn.getURL());
System.out.println("HTTP response code received: "+conn.getResponseCode());
System.out.println("HTTP response message received: "+conn.getResponseMessage());
} finally {
if (is != null) is.close();
}
}
}
The output of this program is: 該程序的輸出爲：
Original URL: http://httpstat.us/301 Connected to: http://httpstat.us/301 HTTP response code received: 301 HTTP response message received: Moved Permanently
A request to http://httpstat.us/301 returns the following (shortened) response (which seems absolutely right!): 對http://httpstat.us/301的請求返回以下（縮短的）響應（這似乎絕對正確！）：
HTTP/1.1 301 Moved Permanently
Cache-Control: private
Content-Length: 21
Content-Type: text/plain; charset=utf-8
Location: https://httpstat.us
Unfortunately, Java's HttpURLConnection does not follow the redirect! 不幸的是，Java的HttpURLConnection沒有遵循重定向！
Note that if you change the original URL to HTTPS ( https://httpstat.us/301 ), Java will follow the redirect as expected!? 請注意，如果將原始URL更改爲HTTPS（ https://httpstat.us/301 ），Java 將按照預期進行重定向！