Java IO.pdf - Nguyen Dang Binh

Java I/O
public GZIPInputStream(InputStream in) throws IOException
public GZIPInputStream(InputStream in, int bufferLength) throws IOException
Since this is a filter stream, both constructors take an underlying input stream as an argument.
The second constructor also accepts a length for the buffer into which the compressed data
will be read. Otherwise, GZIPInputStream has the usual methods of an input stream: read(),
skip(), close(), mark(), reset(), and so on. Marking and resetting are not supported. Two
methods are overridden, read() and close():
public int read(byte[] data, int offset, int length) throws IOException
public void close() throws IOException
These methods work exactly like the superclass methods they override. The only thing you
need to be aware of is that the read() method blocks until sufficient data is available in the
buffer to allow decompression.
GZIPInputStream has two protected fields that may be accessed from subclasses. The crc
field provides a cyclic redundancy code for that portion of the data that has been decoded.
CRC32 objects are discussed later in this chapter. The eos field is a boolean indicating
whether the end of the stream has been reached. It's initially set to false. It becomes true
once the end of the compressed data has been reached:
protected CRC32 crc;
protected boolean eos;
Finally, there's one not very useful mnemonic constant, GZIPInputStream.GZIP_MAGIC. All
valid gzip files must begin with this number, which helps to identify the file's type:
public static final int GZIP_MAGIC = 0x8B1F;
Example 9.6 shows how easy it is to decompress gzipped data with GZIPInputStream. The
main() method reads a series of filenames from the command line. A FileInputStream
object is created for each file and a GZIPInputStream is chained to that. The data is read
from the file, and the decompressed data is written into a new file with the same name minus
the .gz suffix. (A more robust implementation would handle the case where the suffix is not
.gz .) You can test this program with files gzipped by Example 9.5 and with files gzipped by
the FSF's Gzip program.
Example 9.6. The GUnzipper
import java.io.*;
import java.util.zip.*;
import com.macfaq.io.*;
public class GUnzipper {
public static void main(String[] args) {
for (int i = 0; i < args.length; i++) {
if (args[i].toLowerCase().endsWith(GZipper.GZIP_SUFFIX)) {
try {
FileInputStream fin = new FileInputStream(args[i]);
GZIPInputStream gzin = new GZIPInputStream(fin);
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