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

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出现问题：当getContentLength();返回时-1或者是0时候。

解决办法：需加上conn.setRequestProperty("Accept-Encoding", "identity");

解释：在默认情况下，HttpURLConnection 使用 gzip方式获取，文件 getContentLength()这个方法，每次read完成后可以获得，当前已经传送了多少数据，而不能用这个方法获取需要传送多少字节的内容，当read() 返回 -1时，读取完成，由于这个压缩后的总长度我无法获取，那么进度条就没法计算值了。所以要取得长度则，要求http请求不要gzip压缩

附上一段代码：

 1                 // 临时文件检验, 是否续传文件 2                 filePath = filePath + ".temp"; 3                 long haveDownLength = 0; 4                 File tempFile = new File(filePath); 5                 if (tempFile.exists()) 6                     haveDownLength = tempFile.length(); 7  8                 conn = (HttpURLConnection) new URL(urlString).openConnection(); 9                 if (haveDownLength > 0)10                     conn.setRequestProperty("Connection", "Keep-Alive");11                 conn.setReadTimeout(6000);12                 conn.setConnectTimeout(3000);;13                 conn.setRequestMethod("GET");14                 conn.setRequestProperty("Accept-Encoding", "identity");15                 conn.connect();16 17                 int fileSize = conn.getContentLength();18                 long countRead = haveDownLength;19                 if (conn.getResponseCode() == 200) {20                     InputStream stream = conn.getInputStream();21                     FileOutputStream fos = new FileOutputStream(filePath, haveDownLength > 0 ? true : false);22                     int read = 0;23 24                     byte buffer[] = new byte[1024];25                     while ((read = stream.read(buffer)) >= 0) {26                         countRead += read;27                         fos.write(buffer, 0, (int) read);28                     }29                     fos.flush();30                     stream.close();31                     fos.close();32                 } else {33                     fileSize = (int) haveDownLength;34                 }35                 conn.disconnect();36 37                 int index = filePath.indexOf(".temp");38                 if (index >= 1) {39                     String tempFilePath = filePath.substring(0, index);40                     File renameFile = new File(filePath);41                     File toFile = new File(tempFilePath);42                     renameFile.renameTo(toFile);43 44                     String md5 = ControlDataSourceGlobalUtil.md5sum(tempFilePath);45                     // MD5校验是否文件相同46                     if (md5.compareToIgnoreCase(fileCrc32) != 0){47                         File tempFilePathFile = new File(tempFilePath);48                         tempFilePathFile.delete();49                         return false;50                     }51                     return true;52                 }53             } catch (IOException e) {54                 return false;55             }

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