How do I get HTTP headers using HttpClient HEAD request?

The HTTP HEAD method is used for reading the headers information of a resource returned when accessing it using the HTTP GET method. Such request can be done before deciding to download a large resource to save bandwidth. The response to a HEAD method should not have a body, in the code below we use the HttpResponse.BodyHandlers.discarding(), which is a response body handler that discards the the response body.

In the code snippet below we start by creating an instance of HttpClient, in this example we use the HttpClient.newBuilder().build() method. After creating the HttpClient we create the HttpRequest object. We set the HTTP method to HEAD by calling the method method() and pass a string “HEAD” as the method name and HttpRequest.BodyPublishers.noBody() a request body publisher which sends no request body.

The next step in the code below is to send the request and get the response headers from the HttpResponse object using the headers() method. The map() method of the HttpHeaders object give us a key-values of the headers returned by the server.

package org.kodejava.example.httpclient;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpHeaders;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class HeadRequestExample {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newBuilder().build();

        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://google.com"))
            .method("HEAD", HttpRequest.BodyPublishers.noBody())
            .build();

        HttpResponse<Void> response = client.send(request,
            HttpResponse.BodyHandlers.discarding());

        // Returns an unmodifiable multi map view of this HttpHeaders.
        // The map contains key of string, with list of strings as
        // its value.
        HttpHeaders headers = response.headers();
        headers.map().forEach((key, values) ->
            System.out.printf("%s = %s%n", key, values));
    }
}

Here are the HTTP headers we got and printed out to the console screen:

:status = [301]
alt-svc = [quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000,h3-T050=":443"; ma=2592000]
cache-control = [public, max-age=2592000]
content-length = [220]
content-type = [text/html; charset=UTF-8]
date = [Wed, 22 Apr 2020 14:41:49 GMT]
expires = [Fri, 22 May 2020 14:41:49 GMT]
location = [https://www.google.com/]
server = [gws]
x-frame-options = [SAMEORIGIN]
x-xss-protection = [0]

How do I read website content using HttpClient?

The HTTP Client API can be used to request HTTP resources over the network. This new API was introduced as a new API in Java 11. It supports HTTP/1.1 and HTTP/2 and also support both synchronous and asynchronous programming models. The code snippet below show you how to use the new API to read the content of a website page.

In the code below we start by creating a new instance of HttpClient using the newHttpClient() static method. This is equivalent to calling newBuilder().build(). This give us an instance of HttpClient with default settings like using the “GET” request method the as the default. Then we create an HttpRequest object using the newBuilder() method, set the request URI and call the build() method to build the HttpRequest object.

Next we send the request by calling the send() method of the HttpClient object. This will sends the given request, blocking if necessary to get the response. The returned HttpResponse object contains the response status, headers, and body as handled by given response body handler.

package org.kodejava.example.httpclient;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;

public class ReadWebsiteContent {
    public static void main(String[] args) throws Exception {
        // Creates HttpClient object with default configuration.
        HttpClient httpClient = HttpClient.newHttpClient();

        // Creates HttpRequest object and set the URI to be requested, 
        // when not defined the default request method is the GET request.
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://httpie.org/hello"))
            .GET()
            .build();

        // Sends the request and print out the returned response.
        HttpResponse<String> response = httpClient.send(request,
            HttpResponse.BodyHandlers.ofString(StandardCharsets.UTF_8));

        System.out.println("Status Code: " + response.statusCode());
        System.out.println("Headers    : " + response.headers().toString());
        System.out.println("Body       : " + response.body());
    }
}

Here is the content of the website that we read using the code snippet above:

Status Code: 200
Headers    : java.net.http.HttpHeaders@2d299ad6 { {:status=[200], cf-cache-status=[DYNAMIC], cf-ray=[5875b78d5df2eb00-LAX], cf-request-id=[023d710c5b0000eb00b738f200000001], content-length=[116], content-type=[text/x-rst;charset=utf-8], date=[Tue, 21 Apr 2020 08:25:53 GMT], etag=["234b9a1fe19f125356a5396c8cc72d54493a2eef"], expect-ct=[max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"], server=[cloudflare], set-cookie=[__cfduid=d5bdb6d828be3bb85d0f1f4c2ff81041c1587457553; expires=Thu, 21-May-20 08:25:53 GMT; path=/; domain=.httpie.org; HttpOnly; SameSite=Lax]} }
Body       : 

Hello, World! 👋
~~~~~~~~~~~~~~~~

Thank you for trying out HTTPie 🥳

I hope this will become a friendship.