java 发送form-data请求上传文件代码

我可以为您提供如下 Java 代码示例，用于发送 form-data 请求上传文件：

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;

public class FormDataUploader {

    public static void main(String[] args) {
        String url = "http://example.com/upload";
        String fileName = "test.png";
        File file = new File(fileName);
        String boundary = Long.toHexString(System.currentTimeMillis());
        
        try {
            HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
            connection.setDoOutput(true);
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
            
            OutputStream output = connection.getOutputStream();
            PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, "UTF-8"), true);
            
            writer.append("--" + boundary).append("\r\n");
            writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.getName() + "\"").append("\r\n");
            writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(file.getName())).append("\r\n");
            writer.append("\r\n");
            
            FileInputStream inputStream = new FileInputStream(file);
            byte[] buffer = new byte[4096];
            int bytesRead = -1;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                output.write(buffer, 0, bytesRead);
            }
            output.flush();
            inputStream.close();
            writer.append("\r\n");
            writer.append("--" + boundary + "--").append("\r\n");
            writer.flush();
            writer.close();
            
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line = null;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
            reader.close();
            connection.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

请注意，上传的文件名和请求URL需要根据实际情况进行修改。