How can you add custom headers to requests in HtmlUnit?

HtmlUnit is a headless browser written in Java that is often used for web scraping and testing web applications. Custom headers can often be necessary when making HTTP requests to simulate certain conditions, such as sending a User-Agent string to mimic a particular browser or adding authentication tokens.

To add custom headers to requests in HtmlUnit, you can use the WebRequest class to configure your request before sending it with a WebClient. Here is an example of how you can achieve this:

import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.WebRequest;
import com.gargoylesoftware.htmlunit.html.HtmlPage;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

public class CustomHeadersHtmlUnit {
    public static void main(String[] args) {
        // Create a new web client
        WebClient webClient = new WebClient();

        try {
            // The URL to send the request to
            URL url = new URL("http://example.com");

            // Prepare the request
            WebRequest requestSettings = new WebRequest(url);

            // Set custom headers using the setAdditionalHeader method
            requestSettings.setAdditionalHeader("User-Agent", "Custom User Agent");
            requestSettings.setAdditionalHeader("Authorization", "Bearer your-auth-token");
            requestSettings.setAdditionalHeader("Custom-Header", "Custom Value");

            // You could also add headers using a Map
            Map<String, String> additionalHeaders = new HashMap<>();
            additionalHeaders.put("Another-Header", "Another Value");
            additionalHeaders.put("One-More-Header", "One More Value");
            for (Map.Entry<String, String> header : additionalHeaders.entrySet()) {
                requestSettings.setAdditionalHeader(header.getKey(), header.getValue());
            }

            // Send the request and retrieve the page
            HtmlPage page = webClient.getPage(requestSettings);

            // Do something with the page if needed
            System.out.println(page.asText());

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // It's important to close the web client to free resources
            webClient.close();
        }
    }
}

In the example above, WebRequest is used to set up a new request to http://example.com. Before sending the request with webClient.getPage(requestSettings), custom headers are added to the request using requestSettings.setAdditionalHeader(key, value). You can add as many headers as you like.

Remember that some websites may have security measures in place that could block or limit automated requests. Always respect the website's robots.txt rules and terms of service. Be mindful of legal and ethical considerations when scraping or automating requests.

Also, ensure you're using the latest version of HtmlUnit, as APIs and functionality can change over time. Always refer to the official HtmlUnit documentation for the most up-to-date information.