Java IO.pdf - Nguyen Dang Binh

9.3.3.6 An example
Java I/O
Example 9.11 is an alternative unzipper that uses a ZipInputStream instead of a ZipFile.
There's not really a huge advantage to using one or the other. Use whichever you find more
convenient or aesthetically pleasing.
Example 9.11. Another Unzipper
import java.util.*;
import java.util.zip.*;
import java.io.*;
import com.macfaq.io.*;
public class Unzipper2 {
}
public static void main(String[] args) {
}
for (int i = 0; i < args.length; i++) {
try {
FileInputStream fin = new FileInputStream(args[i]);
ZipInputStream zin = new ZipInputStream(fin);
ZipEntry ze = null;
while ((ze = zin.getNextEntry()) != null) {
System.out.println("Unzipping " + ze.getName());
FileOutputStream fout = new FileOutputStream(ze.getName());
StreamCopier.copy(zin, fout);
zin.closeEntry();
fout.close();
}
zin.close();
}
catch (IOException e) {
System.err.println(e);
e.printStackTrace();
}
}
9.4 Checksums
Compressed files are especially susceptible to corruption. While changing a bit from to 1 or
vice versa in a text file generally only affects a single character, changing a single bit in a
compressed file often makes the entire file unreadable. Therefore, it's customary to store a
checksum with the compressed file so that the recipient can verify that the file is intact. The
zip format does this automatically, but you may wish to use manual checksums in other
circumstances as well.
There are many different checksum schemes. A particularly simple example adds a parity bit
to the data, typically 1 if the number of 1 bits is odd, if the number of 1 bits is even. This
checksum can be calculated by summing up the number of 1 bits and taking the remainder
when that sum is divided by two. However, this scheme isn't very robust. It can detect singlebit
errors, but in the face of bursts of errors as often occur in transmissions over modems and
other noisy connections, there's a 50/50 chance that corrupt data will be reported as correct.
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