How to unzip a file??

[Ann Toh]

Hi,
can anybody tell me how to unzip a file using java codes??
i need to write a java program to unzip a file and read the file inside the zip file. if can, can give me a sample codes to look through. Thanx alot!!

[Malhar Barai]

Hi...
Is that anything related to servlet...!!?? :roll:
Still go through java.Util.zip
There are many classes that would help you.
hth
MB

[David O'Meara]

Moving from Servlets to Java in General (Intermediate)
Dave

[Ann Toh]

Hi,
can show me an example of the program?? cos i hav found some prog, but there are some errors in the program, so i not very sure on how to use it.
Thanx in advance....

[Shashi Kanta]

Hi,
Use java.util.zip.ZipInputStream for unzipping the zip file, and use ZipInputStream.getNextEntry() to get the ZipEntry object representing each file in the zip file. From the ZipEntry object you can get the name of the file inside the .zip file.
-Shashi

[Phil Chuang]

Here you go, my ZipUtil class:
ZipUtil.java

package com.philchuang.utils;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.zip.*;
import java.io.*;
/**
 * Front end for using the java.util.zip package.<BR>
 * For compression/decompression of files.<br> 
 * @author Phil Chuang
 */
public abstract class ZipUtil
{
private static int BUFFERSIZE = 64*1024;
/**
 * Takes files as java.io.File, java.lang.String, or as arrays of either type for multiple sources.<br>
 * Compresses the source file(s) and creates the target zip file.<br>
 * @return compressed file size
 */
public static long zipFile (File source, File target)
{   return zipFiles (new File[] {source}, target);                       }
public static long zipFile (File source, String target)
{   return zipFiles (new File[] {source}, new File(target));             }
public static long zipFile (String source, File target)
{   return zipFiles (new File[] {new File(source)}, target);             }
public static long zipFile (String source, String target)
{   return zipFiles (new File[] {new File(source)}, new File(target));   }
public static long zipFiles (File[] sources, String target)
{   return zipFiles (sources, new File(target));                         }
public static long zipFiles (String[] sources, String target)
{   return zipFiles (sources, new File(target));                         }
public static long zipFiles (String[] sources, File target)
{
try {
if (sources == null) return 0;
File[] files = new File [sources.length];
for (int i = 0; i < sources.length; i++)
files [i] = new File(sources[i]);
return zipFiles (files, target);
} catch (Exception e) { return 0; }
}
public static long zipFiles (File[] sources, File target)
{
try {
int n;
long bytesZipped = 0;
byte[] buffer = new byte[BUFFERSIZE];
if (sources == null) return bytesZipped;
CRC32 crc32 = new CRC32();
ZipOutputStream zipOut = new ZipOutputStream(new FileOutputStream(target));
for (int i = 0; i < sources.length; i++)
{
// calculate CRC32
crc32.reset();
FileInputStream fin = new FileInputStream(sources[i]);
while ((n = fin.read(buffer)) > -1)
crc32.update (buffer, 0, n);
fin.close();
// write zip entry
ZipEntry zipEntry = new ZipEntry(sources[i].getName());
zipEntry.setSize(sources[i].length());
zipEntry.setTime(sources[i].lastModified());
zipEntry.setCrc (crc32.getValue());
zipOut.putNextEntry(zipEntry);
// write zip data
fin = new FileInputStream(sources[i]);
while ((n = fin.read(buffer)) > -1)
zipOut.write(buffer, 0, n);
fin.close();
zipOut.closeEntry();
bytesZipped += zipEntry.getCompressedSize();
}
zipOut.close();
return bytesZipped;
} catch (Exception e) { return 0; }
}
/**
 * Takes the source file(s) as String, File, or array of either, plus the destination directory.<br>
 * Unzips the files into the destination directory.   I don't know how it handles duplicates or overwrites.<br>
 * Currently, no extra options are enabled.<br>
 * @returns the value of the CRC check (good/corrupted)
 */
public static File[] unzipFiles (String[] sources, File directory)
{
if (sources == null) return null;
File[] files = new File [sources.length];
for (int i = 0; i < sources.length; i++)
files [i] = new File(sources[i]);
return unzipFiles (files, directory);
}
public static File[] unzipFiles (File[] sources, String directory)
{   return unzipFiles (sources, new File(directory));             }
public static File[] unzipFiles (String[] sources, String directory)
{   return unzipFiles (sources, new File(directory));             }
public static File[] unzipFile (File source, String directory)
{   return unzipFile (source, new File(directory));               }
public static File[] unzipFile (String source, String directory)
{   return unzipFile (new File (source), new File(directory));    }
public static File[] unzipFile (String source, File directory)
{   return unzipFile (new File (source), directory);              }
public static File[] unzipFiles (File[] sources, File directory)
{
if (sources == null) return null;
boolean validChecksum = true;
Set set = new LinkedHashSet();
for (int i = 0; i < sources.length; i++)
{
File[] newFiles = unzipFile (sources[i], directory);
if (newFiles != null)
for (int j = 0;  j < newFiles.length; j++)
set.add (newFiles [i]);
}
return (File[]) set.toArray (new File [set.size()]);
}
public static File[] unzipFile (File source, File directory)
{
    try {
CRC32 crc32 = new CRC32();
boolean validChecksum = true;
int n;
byte[] buffer = new byte [BUFFERSIZE];
directory.mkdirs();
ZipInputStream zipIn = new ZipInputStream (new FileInputStream (source));
ZipEntry zipEntry = null;
Set fileList = new LinkedHashSet();
while ((zipEntry = zipIn.getNextEntry()) != null)
{
File uncompressedFile = new File(directory.getAbsolutePath()+File.separator+zipEntry.getName());
if (!zipEntry.isDirectory())
{
FileOutputStream fout = new FileOutputStream(uncompressedFile);
crc32.reset();
while ((n = zipIn.read(buffer)) > -1)
{
crc32.update(buffer, 0, n);
fout.write(buffer, 0, n);
}
fout.close();
}
else uncompressedFile.mkdirs();
uncompressedFile.setLastModified(zipEntry.getTime());
if (crc32.getValue() == zipEntry.getCrc())
fileList.add (uncompressedFile);
}
zipIn.close();
return (File[]) fileList.toArray (new File [fileList.size()]);
} catch (Exception e) { return null; }
}
}

[Ann Toh]

Hi,
thanx, i will try and see the program. By the way, does anybody noe how to check whether the file is a zip file?? cos i need to let the user upload their files and i need to check whether the files is a zip file or not. If can, can show an example....
Thanx in advance...

[Phil Chuang]

You could take that unzip method and have it just look through the test file and see if it throws any exceptions i.e. modify it so that it doesn't write the files at all.

[Ann Toh]

Hi,
i try the above codes, but there is no main method. It have 1 error. May I know whether how this program runs??
Thanx in advance....

[ September 03, 2003: Message edited by: Ann Toh ]

[shelly kalra]

Hi Phil,
what is the purpose of using crc in your code?
Thanks,
Shelly.

[Phil Chuang]

Ann:
It is merely a utility class, you don't run it directly, you call it from your own program.
Shelly:
When making a zip file, you calculate a CRC checksum for each file and save it with the zip entry. That way when you unzip a file, you do another CRC checksum and compare it against the checksum for the zip entry, if they do not match then the file is corrupted. The unzip methods originally returned true/false depending on all checksum checks, but I changed it to return a File[] with all the valid unzipped files. I still have some thinking to do as far as error handling, etc.