Password protected zip file in java

Question

I have created zip file using java as below snippet

import java.io.*;
import java.util.zip.*;

public class ZipCreateExample {
  public static void main(String[] args) throws IOException {
    System.out.print("Please enter file name to zip : ");
    BufferedReader input = new BufferedReader
        (new InputStreamReader(System.in));
    String filesToZip = input.readLine();
    File f = new File(filesToZip);
    if(!f.exists()) {
      System.out.println("File not found.");
      System.exit(0);
    }
    System.out.print("Please enter zip file name : ");
    String zipFileName = input.readLine();
    if (!zipFileName.endsWith(".zip"))
      zipFileName = zipFileName + ".zip";
    byte[] buffer = new byte[18024];
    try {
      ZipOutputStream out = new ZipOutputStream
          (new FileOutputStream(zipFileName));
      out.setLevel(Deflater.DEFAULT_COMPRESSION);
      FileInputStream in = new FileInputStream(filesToZip);
      out.putNextEntry(new ZipEntry(filesToZip));
      int len;
      while ((len = in.read(buffer)) > 0) {
        out.write(buffer, 0, len);
      }
      out.closeEntry();
      in.close();
      out.close();
    } catch (IllegalArgumentException iae) {
      iae.printStackTrace();
      System.exit(0);
    } catch (FileNotFoundException fnfe) {
      fnfe.printStackTrace();
      System.exit(0);
    } catch (IOException ioe) {
      ioe.printStackTrace();
      System.exit(0);
    }
  }
}

Now I want when I click on the zip file it should prompt me to type password and then decompress the zip file. Please any help,How should I go further?

Answer 1

Try the following code which is based on Zip4j:

import net.lingala.zip4j.core.ZipFile;
import net.lingala.zip4j.exception.ZipException;
import net.lingala.zip4j.model.ZipParameters;
import net.lingala.zip4j.util.Zip4jConstants;
import org.apache.commons.io.FilenameUtils;

import java.io.File;

public class Zipper
{
    private String password;
    private static final String EXTENSION = "zip";

    public Zipper(String password)
    {
        this.password = password;
    }

    public void pack(String filePath) throws ZipException
    {
        ZipParameters zipParameters = new ZipParameters();
        zipParameters.setCompressionMethod(Zip4jConstants.COMP_DEFLATE);
        zipParameters.setCompressionLevel(Zip4jConstants.DEFLATE_LEVEL_ULTRA);
        zipParameters.setEncryptFiles(true);
        zipParameters.setEncryptionMethod(Zip4jConstants.ENC_METHOD_AES);
        zipParameters.setAesKeyStrength(Zip4jConstants.AES_STRENGTH_256);
        zipParameters.setPassword(password);
        String baseFileName = FilenameUtils.getBaseName(filePath);
        String destinationZipFilePath = baseFileName + "." + EXTENSION;
        ZipFile zipFile = new ZipFile(destinationZipFilePath);
        zipFile.addFile(new File(filePath), zipParameters);
    }

    public void unpack(String sourceZipFilePath, String extractedZipFilePath) throws ZipException
    {
        ZipFile zipFile = new ZipFile(sourceZipFilePath + "." + EXTENSION);

        if (zipFile.isEncrypted())
        {
            zipFile.setPassword(password);
        }

        zipFile.extractAll(extractedZipFilePath);
    }
}

FilenameUtils is from Apache Commons IO.

Example usage:

public static void main(String[] arguments) throws ZipException
{
    Zipper zipper = new Zipper("password");
    zipper.pack("encrypt-me.txt");
    zipper.unpack("encrypt-me", "D:\\");
}

Answer 2

Standard Java API does not support password protected zip files. Fortunately good guys have already implemented such ability for us. Please take a look on this article that explains how to create password protected zip.
(The link was dead, latest archived version: https://web.archive.org/web/20161029174700/http://java.sys-con.com/node/1258827)