Java IO.pdf - Nguyen Dang Binh

9.3.3 The ZipInputStream Class
Java I/O
Zip input streams read data from zip archives, which are most commonly stored in files. As
with output streams, it's generally best not to read the raw data. (If you must read the raw
data, you can always use a bare file input stream.) Instead, the input is first parsed into zip
entries. Once you've positioned the stream on a particular zip entry, you read decompressed
data from it using the normal read() methods. Then the entry is closed, and you open the
next zip entry in the file. The sequence of steps you must follow to read data from a zip input
stream is as follows:
1. Construct a ZipInputStream object from an underlying stream, most commonly a file
input stream.
2. Open the next zip entry in the archive.
3. Read data from the zip entry using InputStream methods like read().
4. Close the zip entry (optional).
5. Repeat steps 2 through 4 as long as there are more entries (files) remaining in the
archive.
6. Close the zip input stream.
Steps 2 and 4, the opening and closing of zip entries in the archive, are new; you won't find
anything like them in other input stream classes. However, attempts to read data from a zip
input stream using only the regular read(), skip(), and close() methods without first
opening a zip entry are doomed to failure.
You probably noticed that the ZipInputStream class provides a second
way to decompress zip files. The ZipFile class approach shown in the
Unzipper program of Example 9.8 is the first. ZipInputStream uses
one input stream to read from successive entries. The ZipFile class
uses different input stream objects for different entries. Which to use is
mainly a matter of aesthetics. There's not a strong reason to prefer one
approach over the other, though the ZipInputStream is somewhat more
convenient in the middle of a sequence of filters.
9.3.3.1 Construct a ZipInputStream
There is a single ZipInputStream() constructor that takes as an argument the underlying
input stream:
public ZipInputStream(InputStream in)
For example:
FileInputStream fin = new FileInputStream("data.zip");
ZipInputStream zin = new ZipInputStream(fin);
No further initialization or parameter setting are needed. A zip input stream can read from a
file regardless of the compression method or level used.
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