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ZIP and UNZIP with Passwords in Java

How to make a password protected zip file and to unzip a password protected zip file in Java

Zip and Unzip are a very common activities for a computer user. A user normally uses the zip utility to compress a directory to create a zip file. There are many ready-made software such as winzip,7zip, and winrar that are available to achieve this. However, it is also possible to protect the zip file with a password so that the end user has to provide the password to unzip the zip file. This is the very common scenario that can be achieved by a zip utility tool. The significant part of my article is to provide you with the solution to achieve this using a Java program. While developing the project you may encounter a scenario in which you have to create a password-protected zip file that can be unzipped by any zip tool like winzip. Let me provide a complete scenario for your understanding.

In a system, some files are generated for a user and all the files are zipped with a password. The generated password protected zip file is sent to the user through email and the password for the zip file to open is sent to the particular user as an SMS to the user's mobile. Similarly the end-user creates a password protected zip file and uploads to a online system with the user's password in a text field. In this case we have to develop a system where the system will be able to create a password protected zip file and should be able to extract all the files from a password protected zip file. Let me show you how you can achieve it.

Technicalities
However, Java provides the feature of creating a zip file and also provides the feature to unzip or decompress a zip file. But there is no default java API to create a password protected zip file and also there is no default java API to unzip a password protected zip file. To facilitate this feature of zip utility some developers have developed java API in this regard. We have to use their API to achieve this. We have to look into the following aspects of zip utility.

  1. Java-enabled system should be able to generate a password protected zip file and that password protected zip file can be unzipped by any zip utility like winzip and others.
  2. Java-enabled system should be able to decompress or unzip a password protected zip file created by any zip utility like winzip and others.

The followings are the APIs you have to use for this objective:

1.To create a password protected zip file in java, you have to use “winzipaes”. It is avilable in Google code. You can download the .jar file and the source code from the following link.

"http://code.google.com/p/winzipaes/"
This API helps to add a password to a already created zip file. It means that if you want to create a password protected zip file, first you have to create a zip file and then you can add a password that zip file. It is a pure java API works with any operating system. You have to download the following jar file from the above URL.

passwordcompressor.jar

2.To unzip or decompress a password protected zip file, you have to use “sevenzipjbind”. It is available in sourceforge.net site. You can download the .jar files from the following link: http://sourceforge.net/projects/sevenzipjbind/files/. This API helps to extract all the files and folders from password protected zip file created by any zip utility tool. You have to download the following .jar files from the above URL.

sevenzipjbinding-AllPlatforms.jar
sevenzipjbinding.jar

3.For password protection, you have to use Bouncecastle cryptographic API. You can download the .jar file from the following link.
http://www.bouncycastle.org/
You have to download the following .jar files from the above URL.
bcprov-jdk15-145.jar

After downloading all the .jar files, put all the .jar files in your classpath. I have written a java program by using all these APIs to achieve all the above mentioned functionalities.

Have a look at the following code structure.

Code for ZipUtil.java
package com.ddlabs.core.zip;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.util.Arrays;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;

import net.sf.sevenzipjbinding.ExtractOperationResult;
import net.sf.sevenzipjbinding.ISequentialOutStream;
import net.sf.sevenzipjbinding.ISevenZipInArchive;
import net.sf.sevenzipjbinding.SevenZip;
import net.sf.sevenzipjbinding.SevenZipException;
import net.sf.sevenzipjbinding.impl.RandomAccessFileInStream;
import net.sf.sevenzipjbinding.simple.ISimpleInArchive;
import net.sf.sevenzipjbinding.simple.ISimpleInArchiveItem;

import de.idyl.crypto.zip.AesZipFileEncrypter;

/**
* This is a utility class having utility method for various kinds of
* zip and unzip operation.
* This class performs the following operations.
* 1. Normal zipping a directory
* 2. Zipping a directory with password
* 3. Normal unzipping a zip file
* 4. Unzipping a password protected zip file

* @author Debadatta Mishra(PIKU)
*
*/
public final class ZipUtil
{
/**This method is used to write the contents from a zip file to a file
* @param file of type
{@link File}
* @param zipIn of type
{@link ZipInputStream}
*/
private static void writeFile( File file , ZipInputStream zipIn)
{
try
{
OutputStream outStream = new FileOutputStream(file);
byte[] buff = new byte[1024];
int len;
while ((len = zipIn.read(buff)) > 0)
{
outStream.write(buff, 0, len);
}
outStream.close();
}
catch (Exception e)
{
e.printStackTrace();
}
}

/**This method is used to extract the zip file to a destination directory
* @param srcZipfile of type
{@link File} indicating the source zip file
* @param destinationDir of type
{@link File} indicating the destination
* directory where the zip file will be extracted.
* @throws IOException
*/
private static void extract(File srcZipfile, File destinationDir) throws IOException
{
ZipInputStream zipIn = null;
try
{
zipIn = new ZipInputStream(new FileInputStream(srcZipfile));
ZipEntry entry = null;

while ((entry = zipIn.getNextEntry()) != null)
{
String outFilename = entry.getName();

if( !new File(destinationDir, outFilename).getParentFile().exists() )
new File(destinationDir, outFilename).getParentFile().mkdirs();

if( !entry.isDirectory() )
writeFile(new File(destinationDir,outFilename), zipIn);
}
System.out.println("Zip file extracted successfully...");
}
catch( Exception e )
{
e.printStackTrace();
}
finally
{
if (zipIn != null)
{
zipIn.close();
}
}
}

/**This method is used to zip or compress a directory to create a zip file.
* @param directory of type String indicating the source directory to be zipped
* @param zos of type
{@link ZipOutputStream}
* @param path of type String indicating the path
* @throws IOException
*/
private static void compressDir(String directory, ZipOutputStream zos, String path) throws IOException {
File zipDir = new File(directory);
String[] dirList = zipDir.list();
byte[] readBuffer = new byte[2156];
int bytesIn = 0;
for (int i = 0; i < dirList.length; i++)
{
File f = new File(zipDir, dirList[i]);
if (f.isDirectory())
{
String filePath = f.getPath();
compressDir(filePath, zos, path + f.getName() + "/");
continue;
}
FileInputStream fis = new FileInputStream(f);
try
{
ZipEntry anEntry = new ZipEntry(path + f.getName());
zos.putNextEntry(anEntry);
bytesIn = fis.read(readBuffer);
while (bytesIn != -1)
{
zos.write(readBuffer, 0, bytesIn);
bytesIn = fis.read(readBuffer);
}
}
catch( Exception e )
{
e.printStackTrace();
}
finally
{
fis.close();
}
}
}

/**This method is used to zip a directory
* @param dirName of type String indicating the path of the directory to be zipped
* @param zipFileName of type String indicating the file name for the zip file
*/
public static void zipDir( String dirName , String zipFileName )
{
if( zipFileName == null )
{
File tempFile = new File(dirName);
zipFileName = tempFile.getAbsoluteFile().getParent()+ File.separator+tempFile.getName()+".zip";
}

try
{
ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFileName));
compressDir(dirName, zos, new File(dirName).getName()+File.separator);
zos.close();
}
catch( NullPointerException npe )
{
npe.printStackTrace();
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch( IOException ie )
{
ie.printStackTrace();
}
}

/**This method is used to create a password protected zip file.
* @param dirName of type String indicating the name of the directory to be zipped
* @param zipFileName of type String indicating the name of the zip file to be created
* @param password of type String indicating the password
*/
public static void zipDirWithPassword( String dirName , String zipFileName , String password)
{
if( zipFileName == null )
{
File tempFile = new File(dirName);
zipFileName = tempFile.getAbsoluteFile().getParent() +File.separator+tempFile.getName()+".zip";
}
zipDir(dirName, zipFileName);
String tempZipFileName = new File( dirName ).getAbsoluteFile() .getParent()+File.separator+"tempencrypted.zip";
try
{
AesZipFileEncrypter enc = new AesZipFileEncrypter (tempZipFileName);
enc.addEncrypted( new File(zipFileName), password);
new File(zipFileName).delete();
new File( tempZipFileName ).renameTo( new File (zipFileName));
}
catch (IOException e)
{
e.printStackTrace();
}
}

/**This method is used to unzip a zip file to a directory
* @param sourceZipFile of type String indicating the source zip file
* @param destinationDir of type String indicating the destination directory
* where the zip file will be extracted.
*/
public static void unzipDir(String sourceZipFile, String destinationDir)
{
try
{
extract( new File(sourceZipFile), new File(destinationDir));
}
catch( Exception e )
{
e.printStackTrace();
}
}

/**This method is used to unzip a password protected zip file.
* @param sourceZipFile of type String indicating the source zip file
* @param destinationDir of type String indicating the directory where
* the zip file will be extracted.
* @param password of type String indicating the password.
*/
public static void unzipDirWithPassword( final String sourceZipFile , final String destinationDir , final String password )
{
RandomAccessFile randomAccessFile = null;
ISevenZipInArchive inArchive = null;
try
{
randomAccessFile = new RandomAccessFile(sourceZipFile, "r");
inArchive = SevenZip.openInArchive(null, // autodetect archive type
new RandomAccessFileInStream(randomAccessFile));

// Getting simple interface of the archive inArchive
ISimpleInArchive simpleInArchive = inArchive.getSimpleInterface();

for (final ISimpleInArchiveItem item : simpleInArchive.getArchiveItems())
{

final int[] hash = new int[] { 0 };
if (!item.isFolder())
{
ExtractOperationResult result;
result = item.extractSlow(new ISequentialOutStream()
{
public int write(final byte[] data) throws SevenZipException
{
try
{
if(item.getPath().indexOf(File.separator)>0)
{
String path = destinationDir+File.separator+item.getPath(). substring(0,item.getPath().lastIndexOf(File.separator));

File folderExisting = new File(path); 
if (!folderExisting.exists())
new File(path).mkdirs();
}
OutputStream out = new FileOutputStream(destinationDir+ File.separator+item.getPath());
out.write(data);
out.close();
}
catch( Exception e )
{
e.printStackTrace();
}
hash[0] |= Arrays.hashCode(data);
return data.length; // Return amount of proceed data
}
},password); /// password.
if (result == ExtractOperationResult.OK)
{
System.out.println(String.format("%9X | %s",
hash[0], item.getPath()));
}
else
{
System.err.println("Error extracting item: " + result);
}
}
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
if (inArchive != null)
{
try
{
inArchive.close();
}
catch (SevenZipException e)
{
System.err.println("Error closing archive: " + e);
e.printStackTrace();
}
}
if (randomAccessFile != null)
{
try
{
randomAccessFile.close();
}
catch (IOException e)
{
System.err.println("Error closing file: " + e);
e.printStackTrace();
}
}
}
}

}

In the above java code, you can achieve the following functionalities.
1.Zip a directory without password like normal zip
2.Zip a directory with password
3.Unzip a zip file to a destination directory
4.Unzip a password protected zip file to a destination directory

Let us look at the Code for the test harness class to test the above functionalities.

Code for TestZipUtil.java
package com.ddlabs.core.zip.test;

import com.ddlabs.core.zip.ZipUtil;

/**This is a test harness class to test all the functionalities defined
* in the ZipUtil class.
* @author Debadatta Mishra(PIKU)
*
*/
public class TestZipUtil
{
public static void main(String[] args)
{
//Normal Zip
//ZipUtil.zipDir("testdata/SWT", "testdata/temp.zip");
//ZipUtil.zipDir("testdata/SWT", null);

//Zip with Password
ZipUtil.zipDirWithPassword("testdata/SWT",  "testdata/temp.zip","abcd1234");
//ZipUtil.zipDirWithPassword("testdata/SWT", null,"abcd1234");

//Normal Unzip
//ZipUtil.unzipDir("testdata/temp.zip", "tempdata");
ZipUtil.unzipDirWithPassword("testdata/temp.zip", "tempdata", "abcd1234");

}

}
In the above test harness class, uncomment the lines as per your desire and test it.

Assumptions
I assume that reader of this article has
Knowledge on Java language
Knowledge on running programs in Eclipse editor

Test Case details
I have tested the above program in the following conditions.
OS Name : Windows Vista
Java : 1.6.0_16
Java Editor : Eclipse 3.5
Zip Utility Tool : Winzip version : 14.0

Conclusion
I hope that you will enjoy my article. This article does not bear any commercial significance , it is only meant for learning and for novice developers. In case of any problem or errors , feel free to contact me in the email debadatta.mishra@gmail.com .

More Stories By Debadatta Mishra

Debadatta Mishra is a senior Java developer with five years of experience in the field of Java and related technologies. He has written many articles on Java-related technologies on the Internet.

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