HttpURLConnection getContentLength();返回時-1或者是0

出現問題：當getContentLength();返回時-1或者是0時候。

解決辦法：需加上conn.setRequestProperty("Accept-Encoding", "identity");

解釋：在默認情況下，HttpURLConnection 使用 gzip方式獲取，文件 getContentLength()這個方法，每次read完成后可以獲得，當前已經傳送了多少數據，而不能用這個方法獲取 需要傳送多少字節的內容，當read() 返回 -1時，讀取完成，由於這個壓縮后的總長度我無法獲取，那么進度條就沒法計算值了。所以要取得長度則，要求http請求不要gzip壓縮

附上一段代碼：

                // 臨時文件檢驗, 是否續傳文件
                filePath = filePath + ".temp";
                long haveDownLength = 0;
                File tempFile = new File(filePath);
                if (tempFile.exists())
                    haveDownLength = tempFile.length();

                conn = (HttpURLConnection) new URL(urlString).openConnection();
                if (haveDownLength > 0)
                    conn.setRequestProperty("Connection", "Keep-Alive");
                conn.setReadTimeout(6000);
                conn.setConnectTimeout(3000);;
                conn.setRequestMethod("GET");
                conn.setRequestProperty("Accept-Encoding", "identity");
                conn.connect();

                int fileSize = conn.getContentLength();
                long countRead = haveDownLength;
                if (conn.getResponseCode() == 200) {
                    InputStream stream = conn.getInputStream();
                    FileOutputStream fos = new FileOutputStream(filePath, haveDownLength > 0 ? true : false);
                    int read = 0;

                    byte buffer[] = new byte[1024];
                    while ((read = stream.read(buffer)) >= 0) {
                        countRead += read;
                        fos.write(buffer, 0, (int) read);
                    }
                    fos.flush();
                    stream.close();
                    fos.close();
                } else {
                    fileSize = (int) haveDownLength;
                }
                conn.disconnect();

                int index = filePath.indexOf(".temp");
                if (index >= 1) {
                    String tempFilePath = filePath.substring(0, index);
                    File renameFile = new File(filePath);
                    File toFile = new File(tempFilePath);
                    renameFile.renameTo(toFile);

                    String md5 = ControlDataSourceGlobalUtil.md5sum(tempFilePath);
                    // MD5校驗是否文件相同
                    if (md5.compareToIgnoreCase(fileCrc32) != 0){
                        File tempFilePathFile = new File(tempFilePath);
                        tempFilePathFile.delete();
                        return false;
                    }
                    return true;
                }
            } catch (IOException e) {
                return false;
            }