java multipart/form-data请求

对于Java中的multipart/form-data请求，您可以使用Java的HttpURLConnection类来发送此类型的请求。下面是一个示例代码片段，展示如何发送multipart/form-data请求：

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

public class MultipartFormDataExample {

    public static void main(String[] args) throws IOException {
        String url = "http://example.com/upload";
        String filePath = "/path/to/file.jpg";

        // 创建URL对象
        URL requestUrl = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) requestUrl.openConnection();

        // 设置请求方法为POST
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);

        String boundary = "---------------------------" + System.currentTimeMillis();

        // 设置请求头
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        // 获取输出流
        OutputStream outputStream = connection.getOutputStream();
        PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream));

        // 添加文件参数
        File file = new File(filePath);
        writer.append("--").append(boundary).append("\r\n");
        writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.getName() + "\"").append("\r\n");
        writer.append("Content-Type: " + HttpURLConnection.guessContentTypeFromName(file.getName())).append("\r\n");
        writer.append("\r\n");
        writer.flush();

        FileInputStream fileInputStream = new FileInputStream(file);
        byte[] buffer = new byte[4096];
        int bytesRead;
        while ((bytesRead = fileInputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
        outputStream.flush();
        fileInputStream.close();

        writer.append("\r\n").flush();

        // 添加其他参数
        writer.append("--").append(boundary).append("\r\n");
        writer.append("Content-Disposition: form-data; name=\"param1\"").append("\r\n");
        writer.append("\r\n");
        writer.append("value1").append("\r\n");
        writer.append("--").append(boundary).append("--").append("\r\n");
        writer.close();

        // 发送请求并获取响应
        int responseCode = connection.getResponseCode();
        BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        StringBuilder response = new StringBuilder();
        while ((line = reader.readLine()) != null) {
            response.append(line);
        }
        reader.close();

        // 打印响应结果
        System.out.println("Response Code: " + responseCode);
        System.out.println("Response: " + response.toString());

        // 关闭连接
        connection.disconnect();
    }
}

您需要将上述代码中的`url`替换为您要上传到的URL，`filePath`替换为要上传的文件路径。此示例还演示了如何添加其他参数到multipart/form-data请求中。

请注意，这只是一个基本示例，实际应用中可能需要进行错误处理、文件大小限制等其他逻辑。