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Create .tar.gz

 
Greenhorn
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This is my first question here .

I am trying to create a .tar.gz file using java programatically. Below code creates .tar.gz but I cannot untar it and gives an error. Could anyone please help me with this code.



I invoke this my calling makeCompress() passing name of parent of directory structure in main method.
Many Thanks
 
Java Cowboy
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Welcome to the Ranch!

Look at lines 10-13, in the method compressFiles.

You have: TarArchiveOutputStream(GZIPOutputStream(BufferedOutputStream(FileOutputStream)))

I think this is the wrong order in which you are wrapping things. A .tar.gz file is a TAR archive which is GZIPped. What you seem to be doing is creating a TAR archive in which each file inside is GZIPped. The GZIPping should be done as the outermost thing instead of the TARing.

In other words, you need: GZIPOutputStream(TarArchiveOutputStream(BufferedOutputStream(FileOutputStream)))
 
indeewari akarawita
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Thank you very much,

I change the order, then should I write to GZIPOutputStream or TarArchiveOutputStream? What are the changes I should made to addFileToCompression method in my program.

I gave a try out only for .tar then program worked only for folders. But if there is any kind of file .tar cannot be extracted.
 
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Jesper de Jong wrote:You have: TarArchiveOutputStream(GZIPOutputStream(BufferedOutputStream(FileOutputStream)))


I think that is correct. Any bytes written to the TarArchiveOutputStream are passed to the GZIPOutputStream, which in turn passes its bytes (after GZIP applied) to the BufferedOutputStream which in turn passed them to the FileOutputStream which finally writes the bytes to disk.

If the TarArchiveOutputStream and GZIPOutputStream are switched you're applying GZIP before applying TAR, which would be something like a .gz.tar file.

The rule is:
- With OutputStream (and Writer), the innermost OutputStream (Writer) will be applied last.
- With InputStream (and Reader), the innermost InputStream (Reader) will be applied first.

Because with .tar.gz TAR must be applied before GZIP, wrapping the GZIPOutputStream in the TarArchiveOutputStream is the correct way. When reading it back in, GZIP must be applied before TAR so the GZIPInputStream would need to be wrapped in the TarArchiveInputStream.
 
Rob Spoor
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Indeewari, how have you been trying to unpack the created .tar.gz? On a UNIX/Linux system using tar -xz?

One more thing: you're not closing the FileInputStreams created on line 44. Using the try-with-resources you can make your code a bit cleaner. Also, declare as List, not ArrayList.
As you can see I only keep a reference to the TarArchiveOutputStream. That's because the other ones are irrelevant. If you close a FilterOutputStream (which is the base class of GZIPOutputStream and BufferedOutputStream) it closes the OutputStream it wraps. TarArchiveOutputStream explicitly mentions that it does the same. So if you close the TarArchiveOutputStream, that closes the GZIPOutputStream which closes the BufferedOutputStream which closes the FileOutputStream. In the end everything is closed.
 
indeewari akarawita
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I tired on Ubuntu; tried both tar -xz command and run extract from right click menu option. Following error prompted.

gzip: stdin: unexpected end of file
tar: Child returned status of 1
tar: Error is not recoverable. exiting now.
 
Rob Spoor
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What works for me (Windows 7, some old Ubuntu, Java 8):
The only important changes are the added .gz to the destination file name, and the way the TarArchiveEntry is created - without the "/" added to the entry name. With the "/" I get a .tar.gz file with only folders, not files.

There's just one issue that remains, and that's an empty folder called ".".
 
indeewari akarawita
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Hi Mr. Spoor,

It worked fine. Thanks a lot for the help.
 
Rob Spoor
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You're welcome
 
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