Java IO.pdf - Nguyen Dang Binh

Java I/O
The ZipFile class contains two constructors. The first takes a filename as an argument. The
second takes a java.io.File object as an argument. File objects will be discussed in
Chapter 12 ; for now, I'll just use the constructor that accepts a filename. Functionally, these
two constructors are similar.
public ZipFile(String filename) throws IOException
public ZipFile(File file) throws ZipException, IOException
ZipException is a subclass of IOException that generally indicates that data in the zip file
doesn't fit the zip format. In this case, the zip exception's message will contain more details,
like "invalid END header signature" or "cannot have more than one drive." While these may
be useful to a zip expert, in general they indicate that the file is corrupted, and there's not
much that can be done about it.
public class ZipException extends IOException
I can discern no reason why the first constructor is declared to throw IOException, while the
second is declared to throw both IOException and ZipException. The second constructor
merely invokes the first after converting the File object to a string pathname. Since
ZipException extends IOException, your code can catch either ZipException and
IOException or just IOException, as your needs dictate.
Both constructors attempt to open the specified file for random access. If the file is opened
successfully with no exceptions, the entries() method will return a list of all the files in the
archive:
public Enumeration entries()
The return value is a java.util.Enumeration object containing one
java.util.zip.ZipEntry object for each file in the archive. Example 9.7 lists the entries in
a zip file specified on the command line. The toString() method is used implicitly to
provide the name for each zip entry in the list.
Example 9.7. ZipLister
import java.util.*;
import java.util.zip.*;
import java.io.*;
public class ZipLister {
public static void main(String[] args) {
for (int i = 0; i < args.length; i++) {
try {
ZipFile zf = new ZipFile(args[i]);
Enumeration e = zf.entries();
while (e.hasMoreElements()) {
System.out.println(e.nextElement());
}
}
160