Java：在 URLConnection 中恢复下载
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Java: resume Download in URLConnection
提问by RYN
I wrote a program that downloads some files from some servers.
Currently program works properly.
But I want to add resume support to it.
I'm doing it like this But the result file is corrupted:
我写了一个程序，从一些服务器下载一些文件。
目前程序运行正常。
但我想为其添加简历支持。
我是这样做的 但结果文件已损坏：
....
File fcheck=new File(SaveDir+"/"+filename);
if(resumebox.isSelected() && fcheck.exists()){
connection.setRequestProperty("Range", "Bytes="+(fcheck.length())+"-");
}
connection.setDoInput(true);
connection.setDoOutput(true);
BufferedInputStream in = new BufferedInputStream (connection.getInputStream());
pbar.setIndeterminate(false);
pbar.setStringPainted(true);
java.io.FileOutputStream fos ;
if(resumebox.isSelected()){
if(fcheck.exists()){
if(connection.getHeaderField("Accept-Ranges").equals("bytes")){
fos = new java.io.FileOutputStream(SaveDir+"/"+filename,true);
}else{
fos = new java.io.FileOutputStream(SaveDir+"/"+filename);
}
}else{
fos = new java.io.FileOutputStream(SaveDir+"/"+filename);
}
}else{
fos = new java.io.FileOutputStream(SaveDir+"/"+filename);
}
....
I'm Testing it on a server that I know supports resume.
I downloaded some bytes.(72720)
Then Tried to resume it.
Then I opened file with a Hex editor , At offset 72720 the first Bytes are repeated:
Bytes 0-36: FLV.............?..........onMetaData
Bytes 72720-72756: FLV.............?..........onMetaData
It Starts download from the begining!
While when I do it by wget it does correctly and responses by Content-Range field!
Server responses with "302 FOUND" and a "206 Partial Content" in wget log.
Can "302 FOUND" cause the problem?
我正在我知道支持简历的服务器上测试它。
我下载了一些字节。(72720)
然后尝试恢复它。
然后我用十六进制编辑器打开文件，在偏移量 72720 处重复第一个字节：
字节 0-36：FLV........................onMetaData
Bytes 72720-72756：FLV..................onMetaData 从头
开始下载！
当我通过 wget 执行它时，它会正确执行并通过 Content-Range 字段进行响应！
wget 日志中的服务器响应为“302 FOUND”和“206 Partial Content”。
“302 FOUND”会导致问题吗？
What is the problem ?
Thanks.
问题是什么 ？
谢谢。
回答by NG.
Try:
尝试：
connection.setRequestProperty("Range", "bytes=" + fcheck.length() + "-");
Lowercase the range specifier per the spec. Also, if your partial file was 500 bytes, that means your byte range that you have is 0-499, and you want 500+.
根据规范小写范围说明符。此外，如果您的部分文件是 500 字节，这意味着您拥有的字节范围是 0-499，而您想要 500+。
回答by Maurice Perry
The problem is in (fcheck.length() - 1): this should be fcheck.length().
问题在于(fcheck.length() - 1)：这应该是fcheck.length()。
