我们如何获取指定 URL 的响应头信息呢？

代码如下

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() );}
}

结果输出

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