Java - URLConnection getHeaderFieldKey(int n)

Description

The Java URLConnection getHeaderFieldKey(int n) method returns the key for the n^th header field. It returns null if there are fewer than n+1 fields.

Declaration

Following is the declaration for java.net.URLConnection.getHeaderFieldKey(int n) method

public String getHeaderFieldKey(int n)

Parameters

n − an index, where n >= 0.

Return Value

the key for the n^th header field, or null if there are fewer than n+1 fields.

Exception

NA

Example 1

The following example shows the usage of Java URLConnection getHeaderFieldKey(int n) method for a valid url with https protocol. In this example, we're creating an instance of URL class. Using url.openConnection() method, we're getting the URLConnection instance. Using getHeaderFieldKey(), we're getting the keys and using getHeaderField() the value of all header fields of URLConnection instance and printing the same −

package com.tutorialspoint;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;

public class UrlConnectionDemo {
   public static void main(String [] args) {
      try {
         URL url = new URL("https://www.tutorialspoint.com");
         URLConnection urlConnection = url.openConnection();
         for (int i = 0;; i++) {
            String headerName = urlConnection.getHeaderFieldKey(i);
            String headerValue = urlConnection.getHeaderField(i);
            if (headerName == null && headerValue == null) {
               break;
            }
            System.out.println(headerName + ":" + headerValue);
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Let us compile and run the above program, this will produce the following result −

Output

null:HTTP/1.1 200 OK
Access-Control-Allow-Origin:*
Access-Control-Allow-Origin:*;
Age:165900
Cache-Control:max-age=2592000
Content-Type:text/html; charset=UTF-8
Date:Wed, 06 Dec 2023 05:11:49 GMT
Expires:Fri, 05 Jan 2024 05:11:49 GMT
Last-Modified:Mon, 04 Dec 2023 07:06:49 GMT
Server:ECAcc (ndl/D383)
Vary:Accept-Encoding
X-Cache:HIT
X-Frame-Options:SAMEORIGIN
X-Version:OCT-10 V1
X-XSS-Protection:1; mode=block
Content-Length:293801

Example 2

The following example shows the usage of Java URLConnection getHeaderFieldKey(int n) method for a valid url with http protocol. In this example, we're creating an instance of URL class. Using url.openConnection() method, we're getting the URLConnection instance. Using getHeaderFieldKey(), we're getting the keys and using getHeaderField() the value of all header fields of URLConnection instance and printing the same −

package com.tutorialspoint;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;

public class UrlConnectionDemo {
   public static void main(String [] args) {
      try {
         URL url = new URL("https://www.tutorialspoint.com");
         URLConnection urlConnection = url.openConnection();
         for (int i = 0;; i++) {
            String headerName = urlConnection.getHeaderFieldKey(i);
            String headerValue = urlConnection.getHeaderField(i);
            if (headerName == null && headerValue == null) {
               break;
            }
            System.out.println(headerName + ":" + headerValue);
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Let us compile and run the above program, this will produce the following result −

Output

null:HTTP/1.1 200 OK
Access-Control-Allow-Origin:*
Access-Control-Allow-Origin:*;
Age:166167
Cache-Control:max-age=2592000
Content-Type:text/html; charset=UTF-8
Date:Wed, 06 Dec 2023 05:16:16 GMT
Expires:Fri, 05 Jan 2024 05:16:16 GMT
Last-Modified:Mon, 04 Dec 2023 07:06:49 GMT
Server:ECAcc (ndl/D383)
Vary:Accept-Encoding
X-Cache:HIT
X-Frame-Options:SAMEORIGIN
X-Version:OCT-10 V1
X-XSS-Protection:1; mode=block
Content-Length:293801

Example 3

The following example shows the usage of Java URLConnection getHeaderFieldKey(int n) method for a valid url with http protocol. In this example, we're creating an instance of URL class. Using url.openConnection() method, we're getting the URLConnection instance. Using getHeaderFieldKey(), we're getting the keys and using getHeaderField() the value of all header fields of URLConnection instance and printing the same −

package com.tutorialspoint;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.time.Instant;
import java.util.Date;

public class UrlConnectionDemo {
   public static void main(String [] args) {
      try {
         URL url = new URL("http://www.google.com");
         URLConnection urlConnection = url.openConnection();
         for (int i = 0;; i++) {
            String headerName = urlConnection.getHeaderFieldKey(i);
            String headerValue = urlConnection.getHeaderField(i);
            if (headerName == null && headerValue == null) {
               break;
            }
            System.out.println(headerName + ":" + headerValue);
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Let us compile and run the above program, this will produce the following result −

Output

null:HTTP/1.1 200 OK
Date:Wed, 06 Dec 2023 05:13:35 GMT
Expires:-1
Cache-Control:private, max-age=0
Content-Type:text/html; charset=ISO-8859-1
Content-Security-Policy-Report-Only:object-src 'none';...
P3P:CP="This is not a P3P policy! See g.co/p3phelp for more info."
Server:gws
X-XSS-Protection:0
X-Frame-Options:SAMEORIGIN
Set-Cookie:1P_JAR=2023-12-06-05; expires=Fri, 05-Jan-2024 05:13:35 GMT;...
Set-Cookie:AEC=Ackid1S2Iur-...HttpOnly; SameSite=lax
Set-Cookie:...
Accept-Ranges:none
Vary:Accept-Encoding
Transfer-Encoding:chunked