This example shows you how to get the Http response header values in Java.

1. Standard JDK example.

	URL obj = new URL("http://mkyong.com");
	URLConnection conn = obj.openConnection();
 
	//get all headers
	Map<String, List<String>> map = conn.getHeaderFields();
	for (Map.Entry<String, List<String>> entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + 
                 " ,Value : " + entry.getValue());
	}
 
	//get header by 'key'
	String server = conn.getHeaderField("Server");

2. Apache HttpClient example.

	HttpClient client = HttpClientBuilder.create().build();
	HttpGet request = new HttpGet("http://mkyong.com");
	HttpResponse response = client.execute(request);
 
	//get all headers		
	Header[] headers = response.getAllHeaders();
	for (Header header : headers) {
		System.out.println("Key : " + header.getName() 
		      + " ,Value : " + header.getValue());
	}
 
	//get header by 'key'
	String server = response.getFirstHeader("Server").getValue();

1. URLConnection Example

See a full example to get response headers value via URLConnection.

ResponseHeaderUtil.java
package com.mkyong;
 
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;
 
public class ResponseHeaderUtil {
 
  public static void main(String[] args) {
 
    try {
 
	URL obj = new URL("http://mkyong.com");
	URLConnection conn = obj.openConnection();
	Map<String, List<String>> map = conn.getHeaderFields();
 
	System.out.println("Printing Response Header...\n");
 
	for (Map.Entry<String, List<String>> entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() 
                           + " ,Value : " + entry.getValue());
	}
 
	System.out.println("\nGet Response Header By Key ...\n");
	String server = conn.getHeaderField("Server");
 
	if (server == null) {
		System.out.println("Key 'Server' is not found!");
	} else {
		System.out.println("Server - " + server);
	}
 
	System.out.println("\n Done");
 
    } catch (Exception e) {
	e.printStackTrace();
    }
 
  }
}

Output

Printing Response Header...
 
Key : null ,Value : [HTTP/1.1 200 OK]
Key : ETag ,Value : ["713cd-9b82-4dd6d789447c0"]
Key : Content-Length ,Value : [39810]
Key : Expires ,Value : [Fri, 24 May 2013 03:22:31 GMT]
Key : Last-Modified ,Value : [Fri, 24 May 2013 02:22:31 GMT]
Key : Connection ,Value : [Keep-Alive]
Key : X-Powered-By ,Value : [W3 Total Cache/0.9.2.9]
Key : Server ,Value : [Apache/2.2.22 (Unix) mod_ssl/2.2.22 OpenSSL/1.0.0-fips mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635]
Key : Pragma ,Value : [public]
Key : Cache-Control ,Value : [public]
Key : Date ,Value : [Fri, 24 May 2013 02:22:37 GMT]
Key : Vary ,Value : [Accept-Encoding,Cookie]
Key : Keep-Alive ,Value : [timeout=2, max=100]
Key : Content-Type ,Value : [text/html]
Key : Accept-Ranges ,Value : [bytes]
 
Get Response Header By Key ...
 
Server - Apache/2.2.22 (Unix) mod_ssl/2.2.22 OpenSSL/1.0.0-fips mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
 
Done

2. Apache HttpClient Example

This is an equivalent example, but using Apache HttpClient.

ResponseHeaderUtil.java
package com.mkyong;
 
import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
 
public class ResponseHeaderUtil {
 
  public static void main(String[] args) {
 
    try {
 
	HttpClient client = HttpClientBuilder.create().build();
	HttpGet request = new HttpGet("http://mkyong.com");
	HttpResponse response = client.execute(request);
 
	System.out.println("Printing Response Header...\n");
 
	Header[] headers = response.getAllHeaders();
	for (Header header : headers) {
		System.out.println("Key : " + header.getName() 
                           + " ,Value : " + header.getValue());
 
	}
 
	System.out.println("\nGet Response Header By Key ...\n");
	String server = response.getFirstHeader("Server").getValue();
 
	if (server == null) {
		System.out.println("Key 'Server' is not found!");
	} else {
		System.out.println("Server - " + server);
	}
 
	System.out.println("\n Done");
 
    } catch (Exception e) {
	e.printStackTrace();
    }
  }
}

References

  1. Wiki : List of HTTP header fields
  2. How To Get HTTP Request Header In Java
  3. URLConnection.html#getHeaderFields() Java Doc
  4. Apache Http Components – HttpClient
  5. How To Send HTTP Request GET/POST In Java
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