Using Java to solve captchas with CS

In this example, we're setting up a HttpURLConnection object to send the POST request to the server. We're then constructing the form data with the image attached using a unique boundary identifier.

Once we have the form data constructed, we set the appropriate headers for the request, including the content length and content type with the boundary identifier.

After sending the HTTP POST request, we read the response from the server as text, just like in the JavaScript example.

Note that this example uses Java's built-in Base64 class to decode the image from its base64-encoded representation.

import java.io.BufferedReader;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.URL;import java.nio.charset.StandardCharsets;import java.util.Base64;
public class ImageUploader {  public static void main(String[] args) throws IOException {    // Base64-encoded representation of the image you want to upload    String pict= "data:image/png;base64,iVBORw0KG...";    // Set up the URL and connection
    URL url = new URL("http://127.0.0.1:80");    HttpURLConnection connection = (HttpURLConnection) url.openConnection();    connection.setRequestMethod("POST");    connection.setDoOutput(true);
    // Set up the form data with the image and other variables attached    String boundary = Long.toHexString(System.currentTimeMillis()); // unique boundary identifier    byte[] boundaryBytes = ("\r\n--" + boundary + "\r\n").getBytes(StandardCharsets.UTF_8);    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();    outputStream.write(boundaryBytes);    outputStream.write(("Content-Disposition: form-data; name=\"image\"; filename=\"image.png\"\r\n" +        "Content-Type: image/png\r\n\r\n").getBytes(StandardCharsets.UTF_8));    outputStream.write(Base64.getDecoder().decode(pict.split(",")[1]));    outputStream.write(boundaryBytes);    outputStream.write(("Content-Disposition: form-data; name=\"name\"\r\n\r\n" + name).getBytes(StandardCharsets.UTF_8));    outputStream.write(boundaryBytes);    outputStream.write(("Content-Disposition: form-data; name=\"email\"\r\n\r\n" + email).getBytes(StandardCharsets.UTF_8));    outputStream.write(boundaryBytes);
    byte[] requestBody = outputStream.toByteArray();    byte[] requestFooter = ("\r\n--" + boundary + "--\r\n").getBytes(StandardCharsets.UTF_8);    int contentLength = requestBody.length + requestFooter.length;    connection.setRequestProperty("Content-Length", Integer.toString(contentLength));    connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
    // Send the HTTP request    connection.getOutputStream().write(requestBody);    connection.getOutputStream().write(requestFooter);
    // Read the response from the server    InputStream inputStream = connection.getInputStream();    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));    StringBuffer responseBuffer = new StringBuffer();    String line;    while ((line = reader.readLine()) != null) {      responseBuffer.append(line);    }    String response = responseBuffer.toString();
    System.out.println("Response: " + response);  }}