Java 獲取 URL 響應頭信息

我們如何獲取指定 URL 的響應頭信息呢？

代碼如下

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Map;
import java.util.Set;
 
public class Main {
    public static void main(String[] args) throws IOException{
        URL url = new URL("http://www.baidu.com");
        URLConnection conn = url.openConnection();
        
        Map headers = conn.getHeaderFields();
        Set<String> keys = headers.keySet();
        for( String key : keys ){
            String val = conn.getHeaderField(key);
            System.out.println(key+"    "+val);
        }
        System.out.println( conn.getLastModified() );
    }
}

結果輸出

null    HTTP/1.1 200 OK
Server    bfe
Content-Length    2381
Date    Sat, 18 Apr 2020 10:06:39 GMT
Content-Type    text/html
0