Java HttpURLConnection错误网关：502错误

我有一个服务器来接收媒体jpg格式和mp4格式。交付是通过HttpURLConnection进行的。据我所知，这是使用http和https文件传输的最佳解决方案。尝试使用以下代码通过http工作：

FileInputStream fileInputStream = new FileInputStream(new File(sourceFileUri) );

        URL url = new URL(uploadURL);
        connection = (HttpURLConnection) url.openConnection();

        connection.setDoInput(true);
        connection.setDoOutput(true);
        connection.setUseCaches(false);

        connection.setRequestMethod("POST");

        connection.setRequestProperty("Connection", "Keep-Alive");
        connection.setRequestProperty("Content-Type", "multipart/form-data;boundary="+boundary);

        outputStream = new DataOutputStream( connection.getOutputStream() );
        outputStream.writeBytes(twoHyphens + boundary + lineEnd);
        outputStream.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\"" + sourceFileUri +"\"" + lineEnd);
        outputStream.writeBytes(lineEnd);

        bytesAvailable = fileInputStream.available();
        bufferSize = Math.min(bytesAvailable, maxBufferSize);
        buffer = new byte[bufferSize];

        bytesRead = fileInputStream.read(buffer, 0, bufferSize);

        Log.d(TAG, String.valueOf(bytesRead));

        while (bytesRead > 0)
        {
            outputStream.write(buffer, 0, bufferSize);
            bytesAvailable = fileInputStream.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);
        }

        outputStream.writeBytes(lineEnd);
        outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

        fileInputStream.close();
        outputStream.close();FileInputStream fileInputStream = new FileInputStream(new File(sourceFileUri) );

        URL url = new URL(uploadURL);
        connection = (HttpURLConnection) url.openConnection();

        connection.setDoInput(true);
        connection.setDoOutput(true);
        connection.setUseCaches(false);

        connection.setRequestMethod("POST");

        connection.setRequestProperty("Connection", "Keep-Alive");
        connection.setRequestProperty("Content-Type", "multipart/form-data;boundary="+boundary);

        outputStream = new DataOutputStream( connection.getOutputStream() );
        outputStream.writeBytes(twoHyphens + boundary + lineEnd);
        outputStream.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\"" + sourceFileUri +"\"" + lineEnd);
        outputStream.writeBytes(lineEnd);

        bytesAvailable = fileInputStream.available();
        bufferSize = Math.min(bytesAvailable, maxBufferSize);
        buffer = new byte[bufferSize];

        bytesRead = fileInputStream.read(buffer, 0, bufferSize);

        Log.d(TAG, String.valueOf(bytesRead));

        while (bytesRead > 0)
        {
            outputStream.write(buffer, 0, bufferSize);
            bytesAvailable = fileInputStream.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);
        }

        outputStream.writeBytes(lineEnd);
        outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

        fileInputStream.close();
        outputStream.close();

一旦我对传入的位流文件进行了记录，我就会得到一个服务器错误“502坏网关”。这部分代码有什么问题？我找了5个小时的问题，但什么也没找到