java发送post请求，使用multipart/form-data格式文件数据到接口

在Java中，你可以使用HttpURLConnection或者第三方库如Apache HttpClient来发送POST请求。以下是使用HttpURLConnection发送带有文件的multipart/form-data请求的示例代码：

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
 
public class MultipartFormDataExample {
    public static void main(String[] args) {
        String boundary = Long.toHexString(System.currentTimeMillis());
        String CRLF = "\r\n"; // 换行符
        String charset = "UTF-8"; // 设置编码
 
        URL url = null;
        HttpURLConnection connection = null;
        OutputStream outputStream = null;
        InputStream inputStream = null;
 
        try {
            url = new URL("http://your-api-endpoint.com"); // 替换为你的API端点
            connection = (HttpURLConnection) url.openConnection();
            connection.setDoOutput(true);
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
 
            outputStream = connection.getOutputStream();
            outputStream.write(("--" + boundary + CRLF).getBytes(charset));
            outputStream.write(String.format("Content-Disposition: form-data; name=\"file\"; filename=\"%s\"%s", "file.txt", CRLF).getBytes(charset));
            outputStream.write(String.format("Content-Type: %s%s", "text/plain", CRLF).getBytes(charset));
            outputStream.write(CRLF.getBytes(charset));
 
            // 写入文件内容
            File file = new File("path/to/your/file.txt"); // 替换为你的文件路径
            FileInputStream fileInputStream = new FileInputStream(file);
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = fileInputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            fileInputStream.close();
 
            // 结束multipart数据
            outputStream.write(