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Java Forum / General / March 2007Compress, Zip a stream which is not a file
Hello, I need to compress a ByteArrayOuputStream (PDF) without saving it on the disk, so I need to zip a stream which won't be convert as a file. Do you know if it is possible ? thx ! Hi, > Hello, > [quoted text clipped - 3 lines] > > thx ! Of course. Take a look at jdk1.5.0-docs\api\java\util\zip\package-summary.html Ciao, Ingo Hi Ingo, I see how to create a zip thx to a zipentry object which is created from a file, but I don't understand how to do it from a different stream, can u help me with that ? thx Hi helene, > Hi Ingo, > > I see how to create a zip thx to a zipentry object which is created > from a file, but I don't understand how to do it from a different > stream, can u help me with that ? thx ZipOutputStream zip=new ZipOutputStream(...); zip.putNextEntry(new ZipEntry(name)); zip.write(bs,0,bs.length); zip.close(); What exactly do you not understand? Ciao, Ingo > Hi helene, > [quoted text clipped - 13 lines] > Ciao, > Ingo In the code you just gave, the ZipEntry constructor takes as argument the file name, doesn't it? but I need to compress a stream which is not a file it will be a stream i just created and that I need to compress and send right away. .. > ...the ZipEntry constructor takes as argument > the file name, doesn't it? A 'string' that might represent the name.. <http://java.sun.com/javase/6/docs/api/java/util/zip/ ZipEntry.html#constructor_summary> (if the bytes do not have a name, make one up!) Andrew T. > .. > [quoted text clipped - 7 lines] > > Andrew T. Hello Andrew, I don't think the string is any name, I think this is the file name you want to compress. I tested it and if I change the string value i get a zip file with a wrong file inside. > In the code you just gave, the ZipEntry constructor takes as argument > the file name, doesn't it? but I need to compress a stream which is > not a file it will be a stream i just created and that I need to > compress and send right away. Do you want to create a ZIP-format archive at all ? If not then chances are that either: http://java.sun.com/javase/6/docs/api/java/util/zip/DeflaterOutputStream.html or: http://java.sun.com/javase/6/docs/api/java/util/zip/DeflaterOutputStream.html is what you want. All those classes (including ZipOutputStream) write to a java.io,OutputStream, which can point to memory, or an external file, or anything else. See the JavaDoc. -- chris Hi, > In the code you just gave, the ZipEntry constructor takes as argument > the file name, doesn't it? but I need to compress a stream which is > not a file it will be a stream i just created and that I need to > compress and send right away. In addition to what Chris said: The String is not more than a 'name'. It is secondary what e.g. a program like WinZip does with that name. You have a Stream, it is zipped and it can have different entries with different names. Not more and not less. Ciao, Ingo > Hello, > [quoted text clipped - 3 lines] > > thx ! If all you want is a compressed stream then gzip format may be better. You can use GZIPOutputStream, which can wrap any OutputStream, to send the data. This stream can be uncompressed by the complementary GZIPInputStream. A Zip stream consists of compressed files in an archive container. It can be streamed, but might not be the most appropriate format if all you want is to compress some data in transit between two end points (a Socket perhaps?).  SignatureNigel Wade, System Administrator, Space Plasma Physics Group, University of Leicester, Leicester, LE1 7RH, UK E-mail : nmw@ion.le.ac.uk Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555 > Hello, > [quoted text clipped - 3 lines] > > thx ! I was under the impression that a PDF is already compressed with a similar algorithm to ZIP compression. You get very little benefit from compressing a compressed file (often times you can only make it bigger) Anyway, Many people have given you the tools you need. ZipEntry indeed specifies a "file name". But that is the "file name" in the .zip file itself. You add the name, and then add the data associated with that name. Just to clarify, a .zip file contains a set of compressed "files"... You can compress arbitrary data in a .zip file, but you need to specify a name for it to work. Alternatively, as Nigel Wade suggested, you can use the GZIP input and output streams. GZIP compression does *not* care about "files". It is probably more appropriate for what you are doing... It is also supported in http. The most popular browsers can automatically uncompress a gzipped response. > I was under the impression that a PDF is already compressed with a > similar algorithm to ZIP compression. You get very little benefit > from compressing a compressed file (often times you can only make it > bigger) PDF supports a compressed format, but it isn't required. Most individually-produced PDFs do seem to use the compressed form, but I don't know what standalone PDF creation libraries do. (My impression is that many such libraries are freeware of one sort or another, and freeware authors have tended to steer clear of potentially patent-encumbered compression formats -- but I've only looked at one such). Even the compressed format is relatively redundant -- I tried a quick experiment and gzipped a hundred or so randomly selected PDFs (actually the contents of my current "papers waiting to be read someday" directory ;-) and gzip compressed them by an average of about 10% each. -- chris > Even the compressed format is relatively redundant -- I tried a quick > experiment and gzipped a hundred or so randomly selected PDFs (actually the > contents of my current "papers waiting to be read someday" directory ;-) and > gzip compressed them by an average of about 10% each. There is a great deal stuff in the PDF format that is not compressed even in the "compressed stuff", because the basic page structure is not compressed, as well as the entire xref table (imagine how much compression that could give!) > Hello, > [quoted text clipped - 3 lines] > > thx ! More see here! http://www.flash50.com/index.php > More see here! That is either missing a comma or it's an exclamation to a bishop that his purview extends farther than previously thought. > http://www.spam...50.com/index.php Spam! Spam! Spam! Spam! -- Lew Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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