微信公众订阅号 上传临时素材示例

        try {

            //声明分割线
            String boundary="-----";

            //准备前期
            File file=new File(filePath);
            URL url=new URL("https://api.weixin.qq.com/cgi-bin/media/upload?access_token=Z_dtsiJWpgghBANNad1B9DS4sgfE9zOLmwIffYmDXDKs4ZWr6wmhX6xYNanplgB8BVsER8JFtRAnJlyc24kDiSfQwMIzIISbWKLHCkQU9ZhXYNokaZchKmA4QOtH6VoBTSBjAAAEDM&type=image");
            URLConnection urlConnection=url.openConnection();
            urlConnection.setDoInput(true);
            urlConnection.setDoOutput(true);
            urlConnection.setUseCaches(false);
            urlConnection.setRequestProperty("Connection","Keep-Alive");
            urlConnection.setRequestProperty("Content-Type","multipart/form-data;boundary="+boundary);
            urlConnection.setRequestProperty("Content-Length",String.valueOf(file.length()));

            //获取文件输入流
            InputStream inputStream=new FileInputStream(file);
            //获取响应输出流
            OutputStream outputStream = urlConnection.getOutputStream();

            //准备写入头信息
            outputStream.write((boundary+"--
").getBytes());
            outputStream.write(("Content-Disposition:form-data;name="media";filename=""+file.getName()+""
").getBytes());
            outputStream.write(("Content-Type:image/jpeg

").getBytes());
            //准备循环写入 文件流
            byte[] b=new byte[1024];
            int l;
            while((l=inputStream.read(b,0,b.length))!=-1){
                outputStream.write(b,0,l);
            }
            outputStream.write(("
"+boundary+"--
").getBytes());

            //关闭
            outputStream.flush();
            outputStream.close();
            inputStream.close();

            urlConnection.connect();

            InputStream is=urlConnection.getInputStream();
            int c;
            while((c=is.read())!=-1){
                System.out.print((char)c);
            }
            is.close();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

特别注意写入文件数据的时候，首尾都需要有分割线，并且分割线比RequestProperty里的Content-Type里的分割线多--个，并且注意换行

其次就是上传的name的值为media字符串

再其次注意请求所附带的参数