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https://issues.apache.org/jira/browse/COMPRESS-291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15101375#comment-15101375
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Dawid Weiss commented on COMPRESS-291:
--------------------------------------
No problem at all, Stefan. I dug into the code, it's actually a lot better at
explaining what's going on in the format than the "official" specification is
({{7zFormat.txt}})...
bq. then "almost random access" to single entries should be possible
Yes, you'd basically have to decode "a bit more" if the required encoded file
is nested somewhere inside a compressed block. This is not an uncommon thing --
"solid" archives in RAR have this property too. The gain is for lots of small
(or very similar) files when the compression dictionary of the encoder is
reused for multiple files.
Like I said, I'll try to fix it for our own purposes -- I'll provide a patch if
I get it working.
> decompress .7z archive very very slow
> -------------------------------------
>
> Key: COMPRESS-291
> URL: https://issues.apache.org/jira/browse/COMPRESS-291
> Project: Commons Compress
> Issue Type: Improvement
> Components: Compressors
> Affects Versions: 1.9
> Environment: Windows 7 x64, jdk1.7.0_21 x64
> Reporter: Robert Jansen
> Priority: Minor
>
> I have 7z archives with one large image and many small files. The following
> code decompresses to a directory and returns the largest file. It is
> glacially slow and not usable for GB size files:
> public File unSevenZipToDir(File sevenZipFile, File outputDir) {
>
> File imgFile = null;
> // Make sure output dir exists
> outputDir.mkdirs();
> if (outputDir.exists()) {
>
> //FileInputStream stream;
> try {
>
> FileOutputStream output = null;
> SevenZFile f7z = new SevenZFile(sevenZipFile);
> SevenZArchiveEntry entry;
> long maxSize = 0;
> while ((entry = f7z.getNextEntry()) != null) {
> if (entry != null) {
> String s = entry.getName();
> if (s != null) {
> long sz =
> entry.getSize();
>
> if (sz > 0) {
> int count;
> byte data[] =
> new byte[4096];
>
> String
> outFileName = outputDir.getPath() + "/"
>
> + new File(entry.getName()).getName();
>
>
>
>
>
>
>
>
>
>
>
>
>
> File outFile =
> new File(outFileName);
>
> // Extract only
> if it does not already exist
> if
> (outFile.exists() == false) {
>
> System.out.println("Extracting " + s + " => size = " + sz);
>
>
>
>
> FileOutputStream fos = new FileOutputStream(
>
> outFile);
>
>
>
> BufferedOutputStream dest = new BufferedOutputStream(
>
> fos);
>
> while
> ((count = f7z.read(data)) != -1) {
>
> dest.write(data, 0, count);
> }
>
>
> dest.flush();
>
> dest.close();
>
> } else {
>
> System.out.println("Using already Extracted " + s + " => size = " + sz);
> }
> if
> (s.endsWith(".h5") || s.endsWith(".tif") ||
>
> s.endsWith(".cos") || s.endsWith(".nitf")
>
> || s.endsWith(".ntf")
>
> || s.endsWith(".jpg") && sz > maxSize) {
> maxSize
> = sz;
> imgFile
> = new File(outFileName);
> }
> } // end sz > 0
> } // end s != null
> } // end if entry
> } // end while
> f7z.close();
> } catch (FileNotFoundException e) {
> // TODO Auto-generated catch block
> e.printStackTrace();
> } catch (IOException e) {
> // TODO Auto-generated catch block
> e.printStackTrace();
> }
> }
> return imgFile;
> }
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