Setting the host header in java httpClient - httpclient

Question

I am trying to set the host header when using java httpClient. I have found that it can be done in apache httpClient using setVirtualHost. How can I do the same with the java httpClient.

Answer 1

The Host-Header is automatically set if you send a request. The following program sends a GET request to httpbin.org/headers and displays the headers which arrived on server side.
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
public class Test {
public static void main(String[] args) throws Exception {
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.uri(new URI("http://httpbin.org/headers"))
.GET()
.build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());
}
}
The output of this program is
{
"headers": {
"Content-Length": "0",
"Host": "httpbin.org",
"Http2-Settings": "AAEAAEAAAAIAAAABAAMAAABkAAQBAAAAAAUAAEAA",
"Upgrade": "h2c",
"User-Agent": "Java-http-client/11.0.2",
"X-Amzn-Trace-Id": "Root=1-5e89b28a-7028ca70c49af58d120493b1"
}
}
You can change the value of the Host field by defining another URI, e.g. if the URI http://www.httpbin.org/headers is used, then the value of the Host header field is www.httpbin.org.
The Host header however cannot be set individually. A set of disallowed headers is defined in class jdk.internal.net.http.common.Utils.
private static final Set<String> DISALLOWED_HEADERS_SET;
static {
// A case insensitive TreeSet of strings.
TreeSet<String> treeSet = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
treeSet.addAll(Set.of("connection", "content-length",
"date", "expect", "from", "host", "upgrade", "via", "warning"));
DISALLOWED_HEADERS_SET = Collections.unmodifiableSet(treeSet);
}