Sending form data using Java 11 HttpClient is fairly straightforward. The HttpClient can be used to send both POST and GET requests, and form data is generally transmitted in POST requests with the application/x-www-form-urlencoded content type.

Here’s how you can send form data using Java 11’s HttpClient:

Example: Sending Form Data

package org.kodejava.net.http;

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

public class HttpClientFormExample {
   public static void main(String[] args) throws Exception {
      // Create the HttpClient
      HttpClient httpClient = HttpClient.newHttpClient();

      // Form parameters
      String formData = "param1=value1&param2=value2";

      // Create the HttpRequest
      HttpRequest request = HttpRequest.newBuilder()
              .uri(URI.create("https://example.com/submit-form"))
              .header("Content-Type", "application/x-www-form-urlencoded")
              .POST(BodyPublishers.ofString(formData))  // Set the request body
              .build();

      // Send the POST request
      HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());

      // Output the response
      System.out.println("Status Code: " + response.statusCode());
      System.out.println("Response Body: " + response.body());
   }
}

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Steps Explained

1. Create the HttpClient: The HttpClient object is used to build and send HTTP requests.

   HttpClient httpClient = HttpClient.newHttpClient();
   

2. Form Data Encoding: The form data must be encoded in application/x-www-form-urlencoded format, e.g., key1=value1&key2=value2. You’ll need to manually build this format or use a utility method to encode special characters (like +, spaces, &, and =). In simple cases:

   String formData = "param1=value1&param2=value2";
   

3. Build the Request:
   • Use HttpRequest.newBuilder() to create your request.
   • Set the URI for the request.
   • Add the Content-Type header for the form data: "application/x-www-form-urlencoded".
   • Use .POST() with BodyPublishers.ofString(formData) to send the body of the request.

   HttpRequest request = HttpRequest.newBuilder()
          .uri(URI.create("https://example.com/submit-form"))
          .header("Content-Type", "application/x-www-form-urlencoded")
          .POST(BodyPublishers.ofString(formData))
          .build();
   

4. Send the Request: Use the HttpClient.send() method to send the request. Provide the HttpResponse.BodyHandlers.ofString() to handle the response body as a plain string.

   HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
   

5. Handle the Response: You can access the HTTP response status code and body.

   System.out.println("Status Code: " + response.statusCode());
   System.out.println("Response Body: " + response.body());
   

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Notes

1. If the form data contains special characters, you should encode them properly using URLEncoder:

   import java.net.URLEncoder;
   
   String param1 = URLEncoder.encode("value1", "UTF-8");
   String param2 = URLEncoder.encode("value2", "UTF-8");
   String formData = "param1=" + param1 + "&param2=" + param2;
   

2. Ensure the target server accepts POST requests with the application/x-www-form-urlencoded content type.

This is all you need to send form data using Java 11’s HttpClient.