如何恢复被中断的下载 - 第二部分

Question

如何恢复被中断的下载 - 第二部分

21

这是我的上一个问题的延续，当时我还不是注册用户。作为提醒，我正在尝试从我的Yahoo!网站服务器恢复大文件的下载，当下载中断时。我先前认为中断是由于100秒超时限制引起的（因为Yahoo！对用户编写的脚本强制执行该时间限制）。然而，当我测量下载中断的时间时，我发现中断时间变化很大（有时下载无间断地运行不到100秒，有时长达七分钟）。所以我不知道超时的原因，只是试图绕过它们。

我尝试了naikus的建议（谢谢），根据http头字段的转储，我的Yahoo!网站服务器似乎确实认识“范围”属性，应该允许在中断处恢复下载。不幸的是，虽然在恢复连接的http头中字节范围看起来正确，但传输的内容总是从文件的开头重新开始。（我的测试文件是一个由50,000个4字节整数组成的数组，从0开始递增。我的下载文件总是从每次下载中断发生的偏移量重新开始计数。） 是否还有其他http连接属性请求，我应该进行以便让Yahoo!服务器实际跳到头部字节范围中指定的文件偏移量？ 这是代码和它的转储：

         // Setup connection.
         URL url = new URL(strUrl[0]);
         URLConnection connection = url.openConnection();
         downloaded = Integer.parseInt(strUrl[3]);
         if (downloaded > 0) {
             connection.setRequestProperty("Range", "bytes="+downloaded+"-");
             connection.connect();
             fileLength = mDownloadFileLength;
             Log.d("AsyncDownloadFile", 
                 "new download seek: " + downloaded +
                 "; lengthFile: " + fileLength);
         }
         else {
             connection.connect();
             downloaded = 0;
             fileLength = connection.getContentLength();
             mDownloadFileLength = fileLength;
         }
         Map<String, List<String>> map = connection.getHeaderFields();
         Log.d("AsyncDownloadFile", "header fields: " + map.toString());

         // Setup streams and buffers.
         input = new BufferedInputStream(url.openStream(), 8192);
         outFile = new RandomAccessFile(strUrl[1], "rw");
         if (downloaded > 0)  
             outFile.seek(downloaded);
         byte data[] = new byte[1024];

         // Download file.
         for (int count=0, i=0; (count=input.read(data, 0, 1024)) != -1; i++) { 
             outFile.write(data, 0, count);
             downloaded += count; 
             if (downloaded >= fileLength)
                 break;

             // Display progress.
             Log.d("AsyncDownloadFile", "bytes: " + downloaded);
             if ((i%10) == 0)
                 publishProgress((int)(downloaded*100/fileLength));
             if (mFlagDisableAsyncTask) {
                 downloaded = 0;
                 break;
             }
         }

         // Close streams.
         outFile.close();
         input.close();

转储：

@ 4:08:24  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[2000000], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:08:33 GMT]}  
D/AsyncDownloadFile( 2372): bytes: 1024  
D/AsyncDownloadFile( 2372): bytes: 1033  
D/AsyncDownloadFile( 2372): bytes: 2057  
D/AsyncDownloadFile( 2372): bytes: 2493  
D/AsyncDownloadFile( 2372): bytes: 3517  
D/AsyncDownloadFile( 2372): bytes: 3953  

.
.
.

@ 4:13:25  
D/AsyncDownloadFile( 2372): bytes: 386473  
D/AsyncDownloadFile( 2372): bytes: 387497  
D/AsyncDownloadFile( 2372): bytes: 387933  
D/AsyncDownloadFile( 2372): new download seek: 387933; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1612067], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:13:29 GMT], co
ntent-range=[bytes 387933-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 388957  
D/AsyncDownloadFile( 2372): bytes: 389981  
D/AsyncDownloadFile( 2372): bytes: 390409  
D/AsyncDownloadFile( 2372): bytes: 391433  
D/AsyncDownloadFile( 2372): bytes: 391869  
D/AsyncDownloadFile( 2372): bytes: 392893  

.
.
.

@ 4:18:45  
D/AsyncDownloadFile( 2372): bytes: 775413  
D/AsyncDownloadFile( 2372): bytes: 775849  
D/AsyncDownloadFile( 2372): bytes: 776873  
D/AsyncDownloadFile( 2372): bytes: 777309  
D/AsyncDownloadFile( 2372): new download seek: 777309; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1222691], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:18:54 GMT], co
ntent-range=[bytes 777309-1999999/2000000]}  
D/dalvikvm( 2372): GC_FOR_MALLOC freed 11019 objects / 470560 bytes in 155ms  
D/AsyncDownloadFile( 2372): bytes: 778333  
D/AsyncDownloadFile( 2372): bytes: 779357  
D/AsyncDownloadFile( 2372): bytes: 779790  
D/AsyncDownloadFile( 2372): bytes: 780814  
D/AsyncDownloadFile( 2372): bytes: 781250  
D/AsyncDownloadFile( 2372): bytes: 782274  

.
.
.

@ 4:23:45  
D/AsyncDownloadFile( 2372): bytes: 1163334  
D/AsyncDownloadFile( 2372): bytes: 1163770  
D/AsyncDownloadFile( 2372): bytes: 1164794  
D/AsyncDownloadFile( 2372): bytes: 1165230  
D/AsyncDownloadFile( 2372): new download seek: 1165230; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[834770], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:23:47 GMT], con
tent-range=[bytes 1165230-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1166246  
D/AsyncDownloadFile( 2372): bytes: 1167270  
D/AsyncDownloadFile( 2372): bytes: 1167706  
D/AsyncDownloadFile( 2372): bytes: 1168730  
D/AsyncDownloadFile( 2372): bytes: 1169754  
D/AsyncDownloadFile( 2372): bytes: 1170778  

.
.
.

@ 4:30:25  
D/AsyncDownloadFile( 2372): bytes: 1551255  
D/AsyncDownloadFile( 2372): bytes: 1551691  
D/AsyncDownloadFile( 2372): bytes: 1552715  
D/AsyncDownloadFile( 2372): bytes: 1553151  
D/AsyncDownloadFile( 2372): new download seek: 1553151; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[446849], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:30:44 GMT], con
tent-range=[bytes 1553151-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1554167  
D/AsyncDownloadFile( 2372): bytes: 1554184  
D/AsyncDownloadFile( 2372): bytes: 1555208  
D/AsyncDownloadFile( 2372): bytes: 1555644  
D/AsyncDownloadFile( 2372): bytes: 1556668  
D/AsyncDownloadFile( 2372): bytes: 1557104  

.
.
.

@ 4:37:10  
D/AsyncDownloadFile( 2372): bytes: 1939188  
D/AsyncDownloadFile( 2372): bytes: 1939624  
D/AsyncDownloadFile( 2372): bytes: 1940648  
D/AsyncDownloadFile( 2372): bytes: 1941084  
D/AsyncDownloadFile( 2372): new download seek: 1941084; lengthFile: 2000000  
D/dalvikvm( 2372): GC_FOR_MALLOC freed 13701 objects / 604600 bytes in 128ms
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[58916], age=[0], server=
[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:37:16 GMT], cont
ent-range=[bytes 1941084-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1942108  
D/AsyncDownloadFile( 2372): bytes: 1942117  
D/AsyncDownloadFile( 2372): bytes: 1943141  
D/AsyncDownloadFile( 2372): bytes: 1943577  
D/AsyncDownloadFile( 2372): bytes: 1944601  
D/AsyncDownloadFile( 2372): bytes: 1945037  

.
.
.

@ 4:38:30  
D/AsyncDownloadFile( 2372): bytes: 1993217  
D/AsyncDownloadFile( 2372): bytes: 1994241  
D/AsyncDownloadFile( 2372): bytes: 1994677  
D/AsyncDownloadFile( 2372): bytes: 1995701  
D/AsyncDownloadFile( 2372): bytes: 1996137  
D/AsyncDownloadFile( 2372): bytes: 1997161  
D/AsyncDownloadFile( 2372): bytes: 1997597  
D/AsyncDownloadFile( 2372): bytes: 1998621  
D/AsyncDownloadFile( 2372): bytes: 1999057  
D/onPostExecute( 2372): download: unsuccessful  

- - -

在BalusC的提示下（感谢），我修改了连接设置，但雅虎服务器仍然在每次中断时重置到文件的开头。以下是更改后的代码和结果转储：

            // Setup connection.
            URL url = new URL(strUrl[0]);
            URLConnection connection = url.openConnection();
            downloaded = Integer.parseInt(strUrl[3]);
            if (downloaded == 0) {
                connection.connect();
                strLastModified = connection.getHeaderField("Last-Modified");
                fileLength = connection.getContentLength();
                mDownloadFileLength = fileLength;
            }
            else {
                connection.setRequestProperty("Range", "bytes=" + downloaded + "-");
                connection.setRequestProperty("If-Range", strLastModified);
                connection.connect();
                fileLength = mDownloadFileLength;
                Log.d("AsyncDownloadFile", 
                        "new download seek: " + downloaded +
                        "; lengthFile: " + fileLength);
            }
            map = connection.getHeaderFields();
            Log.d("AsyncDownloadFile", "header fields: " + map.toString());

转储：

@12:36:40 started  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.c
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTP
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA P
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-m
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[2000000], age=[0], serv
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:36:56 GMT]}  
D/AsyncDownloadFile(  413): bytes: 1024  
D/AsyncDownloadFile(  413): bytes: 2048  
D/AsyncDownloadFile(  413): bytes: 2476  
D/AsyncDownloadFile(  413): bytes: 3500  
D/AsyncDownloadFile(  413): bytes: 3936  

...

@12:39:20 interrupted  
D/AsyncDownloadFile(  413): bytes: 388068  
D/AsyncDownloadFile(  413): bytes: 389092  
D/AsyncDownloadFile(  413): bytes: 389376  
D/AsyncDownloadFile(  413): new download seek: 389376; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1610624], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:39:21 GMT], co
ntent-range=[bytes 389376-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 390400  
D/AsyncDownloadFile(  413): bytes: 390409  
D/AsyncDownloadFile(  413): bytes: 391433  
D/AsyncDownloadFile(  413): bytes: 391869  

...

@12:44:10 interrupted  
D/AsyncDownloadFile(  413): bytes: 775413  
D/AsyncDownloadFile(  413): bytes: 775849  
D/AsyncDownloadFile(  413): bytes: 776873  
D/AsyncDownloadFile(  413): bytes: 777309  
D/AsyncDownloadFile(  413): new download seek: 777309; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1222691], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:44:20 GMT], co
ntent-range=[bytes 777309-1999999/2000000]}  
D/dalvikvm(  413): GC_FOR_MALLOC freed 10869 objects / 465664 bytes in 122ms  
D/AsyncDownloadFile(  413): bytes: 778333  
D/AsyncDownloadFile(  413): bytes: 778342  
D/AsyncDownloadFile(  413): bytes: 779366  
D/AsyncDownloadFile(  413): bytes: 779802  

...

@12:49:30 interrupted  
D/AsyncDownloadFile(  413): bytes: 1163782  
D/AsyncDownloadFile(  413): bytes: 1164806  
D/AsyncDownloadFile(  413): bytes: 1165242  
D/AsyncDownloadFile(  413): new download seek: 1165242; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[834758], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:49:43 GMT], con
tent-range=[bytes 1165242-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 1166266  
D/AsyncDownloadFile(  413): bytes: 1167290  
D/AsyncDownloadFile(  413): bytes: 1167718  
D/AsyncDownloadFile(  413): bytes: 1168742  

...

@12:55:30 interrupted  
D/AsyncDownloadFile(  413): bytes: 1552722  
D/AsyncDownloadFile(  413): bytes: 1553158  
D/AsyncDownloadFile(  413): bytes: 1554182  
D/AsyncDownloadFile(  413): bytes: 1554618  
D/AsyncDownloadFile(  413): new download seek: 1554618; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[445382], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:55:39 GMT], con
tent-range=[bytes 1554618-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 1555642  
D/AsyncDownloadFile(  413): bytes: 1556666  
D/AsyncDownloadFile(  413): bytes: 1557094  
D/AsyncDownloadFile(  413): bytes: 1558118  

...

@12:57:20 interrupted  
D/AsyncDownloadFile(  413): bytes: 1941834  
D/AsyncDownloadFile(  413): bytes: 1942858  
D/AsyncDownloadFile(  413): bytes: 1943882  
D/AsyncDownloadFile(  413): bytes: 1943994  
D/AsyncDownloadFile(  413): new download seek: 1943994; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[56006], age=[0], server=
[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:57:15 GMT], cont
ent-range=[bytes 1943994-1999999/2000000]}  
D/dalvikvm(  413): GC_FOR_MALLOC freed 13617 objects / 602200 bytes in 165ms  
D/AsyncDownloadFile(  413): bytes: 1945018  
D/AsyncDownloadFile(  413): bytes: 1946042  
D/AsyncDownloadFile(  413): bytes: 1946470  
D/AsyncDownloadFile(  413): bytes: 1947494  

...

@12:58:10 finished  
D/AsyncDownloadFile(  413): bytes: 1996103  
D/AsyncDownloadFile(  413): bytes: 1997127  
D/AsyncDownloadFile(  413): bytes: 1997563  
D/AsyncDownloadFile(  413): bytes: 1998587  
D/AsyncDownloadFile(  413): bytes: 1999023  
D/onPostExecute(  413): downloaded: unsuccessful

- gregS

嗨，我有一个问题和你的主题类似，你能帮我看看这个链接的问题吗：https://dev59.com/oVcO5IYBdhLWcg3wvECK？ - DolDurma

3个回答

5

似乎问题出在调用这里。

input = new BufferedInputStream(url.openStream(), 8192);

替代

input = new BufferedInputStream(connection.getInputStream(), 8192);

url.openStream() 调用 openConnection() 方法，但不包含范围属性。

- user1084090

1

我成功地在我的客户端Java应用程序上实现了HTTP恢复下载，关键是使用了“If-Range：original_ETag”请求头，如一个被接受的答案中所述。这里是完整的头部调试信息，它可能有助于您理解恢复工作原理。

服务器的正常回复，文件从开头到结尾读取。ETag值是来自磁盘文件的W /“filesize_bytes-modified_utc”元数据。它可能是其他东西，但这就是Tomcat使用的，通常适用于常规文件内容。

HTTP/1.1 200 OK 
ETag: W/"19097900-1410863319978" 
Last-Modified: Tue, 16 Sep 2014 10:28:39 GMT 
Content-Length: 19097900 
Content-Type: application/octet-stream 
Accept-Ranges: bytes 
Server: Apache-Coyote/1.1 
Date: Wed, 17 Sep 2014 10:39:52 GMT

客户端通过添加范围和If-Range头信息从文件中读取给定的块。字节范围可以是开放式的，因此服务器应该从给定索引开始读取到结尾。请注意，Content-Length不是文件的总长度，而是这个字节块的长度。

Range: bytes=10000000-
If-Range: W/"19097900-1410863319978"

HTTP/1.1 206 Partial Content 
ETag: W/"19097900-1410863319978" 
Last-Modified: Tue, 16 Sep 2014 10:28:39 GMT 
Content-Length: 9097900 
Content-Type: application/octet-stream 
Accept-Ranges: bytes 
Content-Range: bytes 10000000-19097899/19097900 
Server: Apache-Coyote/1.1 
Date: Wed, 17 Sep 2014 18:12:36 GMT

如果远程文件已更改，则服务器不应返回206-PartialContent而是常规的200-OK响应。服务器应使用If-Range值检查一致性。一些客户端（例如VLCPlayer）会在没有If-Range值的情况下放置Range字段。

当客户端进行初始请求时，如果没有Range+If-Range标头，则可能会添加"If-Modified-Since：modified_http_date"标头。服务器可以返回304-NotModified状态，客户端就完成了。如果客户端给定的byteStartIdx>=filesize，那么服务器将返回416-RequestedRangeNotSatisfiable。

提供额外的调试信息以阐明http-resume的工作原理。

Range=bytes=0-0
If-Range=W/"19097900-1410863319978"

HTTP/1.1 206 Partial Content 
ETag=W/"19097900-1410863319978" 
Date=Fri, 19 Sep 2014 12:53:36 GMT 
Content-Length=1 
Last-Modified=Tue, 16 Sep 2014 10:28:39 GMT 
Content-Type=application/octet-stream 
Accept-Ranges=bytes 
Server=Apache-Coyote/1.1 
Content-Range=bytes 0-0/19097900 
- - - - -

Range=bytes=19097800-29097800
If-Range=W/"19097900-1410863319978"

HTTP/1.1 206 Partial Content 
ETag=W/"19097900-1410863319978" 
Date=Fri, 19 Sep 2014 12:59:24 GMT 
Content-Length=100 
Last-Modified=Tue, 16 Sep 2014 10:28:39 GMT 
Content-Type=application/octet-stream 
Accept-Ranges=bytes 
Server=Apache-Coyote/1.1 
Content-Range=bytes 19097800-19097899/19097900 
- - - - - - - - 

Range=bytes=19097899-19097899
If-Range=W/"19097900-1410863319978"

HTTP/1.1 206 Partial Content 
ETag=W/"19097900-1410863319978" 
Date=Fri, 19 Sep 2014 13:01:47 GMT 
Content-Length=1 
Last-Modified=Tue, 16 Sep 2014 10:28:39 GMT 
Content-Type=application/octet-stream 
Accept-Ranges=bytes 
Server=Apache-Coyote/1.1 
Content-Range=bytes 19097899-19097899/19097900

- Whome

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- BalusC · Accepted Answer

要恢复下载，你需要发送的不仅是 Range 请求头，还包括 If-Range 请求头，其中应包含唯一的文件标识符或文件修改时间戳。

如果服务器在初始下载时返回一个 ETag 响应头，则应在后续的恢复请求中使用它作为 If-Range 头。或者如果它返回一个 Last-Modified 响应头，则应该在 If-Range 请求头中使用它。

查看您的日志，服务器已经发送了一个 Last-Modified 响应头。因此，在恢复请求的 If-Range 头中，您应该将其一并发送回去。

// Initial download.
String lastModified = connection.getHeaderField("Last-Modified");

// ...

// Resume download.
connection.setRequestProperty("If-Range", lastModified);

服务器将使用这些信息来验证您是否正在请求完全相同的文件。