JAVA企业微信文件上传返回media_id

机器人发送文件需要先将文件上传，返回media_id

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;

public class WeChatFileUploadTest {
    public static void main(String[] args) {
        File file = new File();//文件路劲
        StringBuilder buffer = new StringBuilder();
        try{
            URL url = new URL("");//机器人文件上传地址
            HttpURLConnection httpUrlConn = (HttpURLConnection) url.openConnection();  //打开链接
            httpUrlConn.setDoInput(true);
            httpUrlConn.setDoOutput(true);
            httpUrlConn.setUseCaches(false);
            httpUrlConn.setRequestProperty("Connection", "Keep-Alive");
            httpUrlConn.setRequestProperty("Charset", "UTF-8");
            String BOUNDARY = "----------" + System.currentTimeMillis();
            httpUrlConn.setRequestProperty("Content-Type","multipart/form-data; boundary="+ BOUNDARY);
            OutputStream outputStream = new DataOutputStream(httpUrlConn.getOutputStream());
            outputStream.write(("--" + BOUNDARY + "\r\n").getBytes(StandardCharsets.UTF_8));
            outputStream.write(("Content-Disposition: form-data; name=\"media\";filelength=\""+ file.length() +"\";filename=\"" + file.getName() + "\"\r\n").getBytes(StandardCharsets.UTF_8));
            outputStream.write("Content-Type: application/octet-stream\r\n\r\n".getBytes(StandardCharsets.UTF_8));
            DataInputStream in = new DataInputStream(Files.newInputStream(file.toPath()));
            int bytes = 0;
            byte[] bufferOut = new byte[1024];
            while ((bytes = in.read(bufferOut)) != -1) {
                outputStream.write(bufferOut, 0, bytes);
            }
            in.close();
            outputStream.write(("\r\n--" + BOUNDARY + "--\r\n").getBytes (StandardCharsets.UTF_8));
            outputStream.flush();
            outputStream.close();
            InputStream inputStream = httpUrlConn.getInputStream();
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String str;
            while ((str = bufferedReader.readLine()) != null) {
                buffer.append(str);
            }
            bufferedReader.close();
            inputStreamReader.close();
            inputStream.close();
            httpUrlConn.disconnect();
        } catch (Exception e) {
            System.out.println("发送POST请求出现异常！" + e);
            e.printStackTrace();
        }
        System.out.println(buffer.toString());
    }
}