如何在 Java HttpURLConnection 中為多部分表單帖子禁用緩沖？

Question

（這是一個簽名的小程序，我決定反對 HTTPClient 保持我的 jar 非常小）

我正在使用 HttpURLConnection 使用多部分表單發布成功地將文件從用戶上傳到服務器。

問題是 HttpURLConnection 正在緩存數據——在發送之前。 因此，當我從文件讀取並寫入 Outputstream 時，它只是在緩沖數據——因此顯示上傳狀態的進度條是完全錯誤的。 但是請注意，表單郵政編碼有效，並且文件正確上傳，返回代碼為 200。

那么如何確保 HttpURLConnection 不會緩存我發送到服務器的數據呢？

這是我的來源：

public UploadResponse send(String formPostUrlStr,String fileFieldName,File targetFile, Map<String, String> valuesMap, UploadStatusListener uploadStatusListener) throws Exception{


    String sendStr=getBoundaryMessage(Boundary,  valuesMap, fileFieldName, targetFile.getName(), valuesMap.get("content-type") );//"image/png") ;

    System.out.println(" multi-part start \n "+ sendStr+ " multi-part end \n");

    String lenstr=Long.toString((long)(sendStr.length()*2)+ targetFile.length());
    System.out.println("Content-Length"+ lenstr);
                        //Content-Length

    URL url= new URL(formPostUrlStr);
    long startTime= System.currentTimeMillis();
    HttpURLConnection s3Connection = (HttpURLConnection) url.openConnection();

    System.out.println("opened url to "+ formPostUrlStr +", connection ok ..");
    s3Connection.setRequestProperty("Content-Type", "multipart/form-data; boundary="
            + Boundary);
    s3Connection.setRequestProperty("content-length",  lenstr);




    s3Connection.setDoOutput(true);
    s3Connection.setDoInput(true);
    s3Connection.setUseCaches(false);
     s3Connection.setInstanceFollowRedirects(true);
    s3Connection.setAllowUserInteraction(true);
    s3Connection.setRequestProperty("User-Agent", "Mozilla/4.5");


    if (uploadStatusListener != null) {
        uploadStatusListener.statusUpdate(targetFile.length(), 0);
    }


    String debugStr= s3Connection.toString();
    System.out.println("conmnection "+ debugStr);


    DataOutputStream httpOut = new DataOutputStream(s3Connection.getOutputStream());

    System.out.println("opened DataOutputStream ok ..");




    httpOut.write(sendStr.getBytes());


    //httpOut.flush();

  System.out.println("httpOut.flush 1 ok ..");
    FileInputStream uploadFileReader = new FileInputStream(targetFile);
    long totalBytes = uploadFileReader.available();
    if (uploadStatusListener != null) {
        uploadStatusListener.statusUpdate(totalBytes, 0);
    }
    System.out.println(" uploading file with size  "+ uploadFileReader.available());
    int bufSize = 102400;
    long availableBytesToRead;
    long totalSent = 0;
    while ((availableBytesToRead = uploadFileReader.available()) > 0) {
        byte[] bufferBytesRead;
        bufferBytesRead = availableBytesToRead >= bufSize ? new byte[bufSize]
                : new byte[(int)availableBytesToRead];
        int count = uploadFileReader.read(bufferBytesRead);
        try{
            httpOut.write(bufferBytesRead);
            totalSent += ((long) count);
            System.out.println(" wrote bytes = "+count+ ", total sent = "+ totalSent +", pendingSize"+ (availableBytesToRead-count) );
        }
        catch(IOException ioe){
            System.out.println(" io exceotion e"+ ioe.getMessage());
            throw ioe;
        }

        //httpOut.flush();
        if (uploadStatusListener != null) {
            uploadStatusListener.statusUpdate(totalBytes, totalSent);
        }

    }
    // FILE DATA END 
    httpOut.write(("--" + Boundary + "--\r\n").getBytes());



    // form end     
    httpOut.write(("--" + Boundary + "--\r\n").getBytes());

    httpOut.flush();
    httpOut.close();

    long endTime= System.currentTimeMillis();

    System.out.println("Completed Writing Data to S3 Connection in "+ (endTime-startTime)+"ms.,now waiting for rsponse code ");
    int code=s3Connection.getResponseCode();
    long endTime2= System.currentTimeMillis();
    System.out.println("Completed Sendind Data to S3 in "+ (endTime2-startTime)+ "ms., rsponse code time "+ (endTime2-endTime)+"ms. ");


    UploadResponse uploadResponse = new UploadResponse();

    uploadResponse.setCode(code);

    System.out.println(" response code : " + code);

    StringBuilder response = new StringBuilder();
    byte[] respBuffer = new byte[4096];


    if (code > 300) {
        if (code == 404) {
            throw new Exception("Error 404");
        }
        BufferedReader err = new BufferedReader(
                new InputStreamReader(s3Connection.getErrorStream()));
        String ret;
        StringBuffer buff = new StringBuffer();
        while ((ret = err.readLine()) != null) {
            buff.append(ret);
        }
        uploadResponse.setMessage(buff.toString());
        System.out.println(" error :"+ buff.toString());
        err.close();


    } else {
        BufferedReader inp = new BufferedReader(
                new InputStreamReader(s3Connection.getInputStream()));
        StringBuffer buff = new StringBuffer();
        String ret;
        while ((ret = inp.readLine()) != null) {
            buff.append(ret);
        }
        inp.close();
        uploadResponse.setMessage(buff.toString());
        if(buff.toString().contains("fail"))
            throw new Exception("Upload failed");
    }        

    System.out.println(response.toString());

    return uploadResponse;        

}

}

Answer 1

我也有同樣的問題。 除了在原始套接字上編寫我的 HTTP 請求之外，我沒有找到任何其他解決方案。 您找到更好的解決方法了嗎？

編輯：我剛剛做了：我們只需要在從 url.openConnection() 獲得的 HttpURLConnection object 上使用 obj.setFixedLengthStreamingMode(12345)，其中 12345 是 POST 請求正文的長度。

Answer 2

作為@Antares 給出的答案的補充，還有另一種方法setChunkedStreamingMode在您事先不知道內容大小時使用。 因此，當您執行 POST 請求時，請在連接上調用該方法：

HttpURLConnection connection = ...
connection.setRequestMethod("POST");
connection.setDoOutput(true);
connection.setChunkedStreamingMode(0);
connection.connect();
... connection.getOutputStream();

這將避免 OutputStream 在開始發送之前緩沖整個內容。