最近在做一個爬蟲專案，需要抓取一些網站的資訊和其中的圖片，抓取過程中發現有一些圖片連結會重定向，而伺服器儲存時不支援重定向，於是想嘗試直接拿到重定向的連結。
藉助Chrome瀏覽器的開發者工具（快捷鍵F12），選擇Network -> Headers，可以看到其重定向後的地址在Response Headers中的Location屬性中。

查閱資料文件可知，
1.類HttpURLConnection提供瞭如下方法：

public void setInstanceFollowRedirects(boolean followRedirects)

Sets whether HTTP redirects (requests with response code 3xx) should be automatically followed by this HttpURLConnection instance.
The default value comes from followRedirects, which defaults to true.
Parameters:
followRedirects a boolean indicating whether or not to follow HTTP redirects.

2.其父類URLConnection有如下方法：

public String getHeaderField(String name)

Returns the value of the named header field.
If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
Parameters:
name the name of a header field.
Returns:
the value of the named header field, or null if there is no such field in the header.

由上可知，可以這樣獲取重定向的連結：
呼叫第一個方法設定false，再呼叫第二個方法設定引數為”Location”，即可獲取重定向的連結地址，程式碼示例：

try {
    URL u = new URL(url);
    HttpURLConnection connection = (HttpURLConnection) u.openConnection();
    connection.setInstanceFollowRedirects(false);
    connection.setConnectTimeout(5000);
    connection.setReadTimeout(5000
 
);
    int code = connection.getResponseCode();
    if(302 == code) {
        String redirectUrl = connection.getHeaderField("Location");
        if(redirectUrl != null && !redirectUrl.isEmpty()) {
            url = redirectUrl;
        }
    }
} catch (Exception e) {
    e.printStackTrace();
}