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A Java library for zip files
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Zip4j - A java library for zip files / streams

Thank you

for rating Zip4j as the best java library for zip files [1, 2, 3, 4]. It has encouraged me to bring this project to life again after a gap of several years. I tried to add some of the important features that were requested over this time, and also made api much more neater. The newer version (> 2.0.0) now supports streams, which was understandably, one of the most requested feature. If you have any feedback, bugs to report, feature requests, etc, please open an issue here on github. I will try to address them as soon as I can. I also monitor the tag zip4j on stackoverflow.

About

Zip4j is the most comprehensive java library for Zip files or streams. As of this writing, it is the only java library which has support for zip encryption, apart from a bunch of other features. It tries to make handling zip files/streams a lot more easier. No more clunky boiler plate code with input streams and output streams. As you can see in the usage section below, working with zip files can now even be a single line of code, compared to this. I mean no offense to the Java's in-built zip support. In fact, this library depends on Java's in-built zip code and it would have been significantly more complicated challenging if I had to write compression logic as well. But lets be honest, working with zip files or streams can be a lot of boiler plate code. The main goal of this library is to provide a simple api for all usual actions of a zip file or streams by doing the heavy lifting within the library and not have developers worry about having to deal with streams, etc. Apart from usability, other important goal of this library is to provide support for as many zip features as possible, which brings me to:

Features

 * Create, Add, Extract, Update, Remove files from a Zip file
 * Support for streams (ZipInputStream and ZipOutputStream)
 * Read/Write password protected Zip files and streams
 * Support for both AES and Zip-Standard encryption methods
 * Support for Zip64 format
 * Store (No Compression) and Deflate compression method
 * Create or extract files from Split Zip files (Ex: z01, z02,...zip)
 * Support for Unicode file names and comments in zip
 * Progress Monitor - for integration into apps and user facing applications

Background

Zip4j was started by me (Srikanth Reddy Lingala) back in 2008/2009, when I realized the lack of support for majority of zip format features in Java. And also working with zip files was, as mentioned several times above, a lot of boiler plate code, having to deal with streams (worse still, it was back in the days when there was no try-with-resources in java). There was also no comprehensive library which supports zip features. So, I decided to write one, and approximately after a year, the first version was out. The response was truly overwhelming, and I got a lot of support right from the next day of release. It was not put on github as git/github was not as popular as it is now. Code was hosted on my website, as, guess what, a zip file :). And unfortunately, after a year or two after the initial release, life got busy and I was not able to support Zip4j as much as I wanted to. But the overwhelming encouragement I got over the years made me start working on Zip4j once again, and makes me support Zip4j as much as I can.

Maven

<dependency>
    <groupId>net.lingala.zip4j</groupId>
    <artifactId>zip4j</artifactId>
    <version>2.0</version>
</dependency>

Please check the latest version number on Zip4j's Maven repository

Usage

Creating a zip file with single file in it / Adding single file to an existing zip

new ZipFile("filename.zip").addFile("filename.ext");

   Or

new ZipFile("filename.zip").addFile("filename.ext");

Creating a zip file with multiple files / Adding multiple files to an existing zip

new ZipFile("filename.zip").addFiles(Arrays.asList(new File("first_file"), new File("second_file")));

Creating a zip file by adding a folder to it / Adding a folder to an existing zip

new ZipFile("filename.zip").addFolder(new File("/user/myuser/folder_to_add"));

Creating a zip file from stream / Adding a stream to an existing zip

new ZipFile("filename.zip").addStream(inputStream, new ZipParameters());

Passing in new ZipParameters(), as in the above example, will make Zip4j use default zip parameters. Please look at ZipParameters to see the default configuration.

Creating a zip file of compression method store / Adding entries to zip file of compression method store

By default Zip4j uses Deflate compression algorithm to compress files. However, if you would like to not use any compression (called STORE compression), you can do so as shown in the example below:

ZipParameters zipParameters = new ZipParameters();
zipParameters.setCompressionMethod(CompressionMethod.STORE);

new ZipFile("filename.zip").addFile("fileToAdd", zipParameters);

You can similarly pass in zip parameters to all the other examples to create a zip file of STORE compression.

Creating a password protected zip file / Adding files to an existing zip with password protection

AES encryption
ZipParameters zipParameters = new ZipParameters();
zipParameters.setEncryptFiles(true);
zipParameters.setEncryptionMethod(EncryptionMethod.AES);
// Below line is optional. AES 256 is used by default. You can override it to use AES 128. AES 192 is supported only for extracting.
zipParameters.setAesKeyStrength(AesKeyStrength.KEY_STRENGTH_256); 

List<File> filesToAdd = Arrays.asList(
    new File("somefile"), 
    new File("someotherfile")
);

ZipFile zipFile = new ZipFile("filename.zip", "password".toCharArray());
zipFile.addFiles(filesToAdd, zipParameters);
Zip Standard encryption:

Instead of AES, replace zipParameters.setEncryptionMethod(EncryptionMethod.AES); with zipParameters.setEncryptionMethod(EncryptionMethod.ZIP_STANDARD);. You can omit the line to set Aes Key strength. As the name suggests, this is only applicable for AES encryption.

In all the above examples, you can similarly pass in zip parameters with appropriate password configuration to create a password protected zip file

Creating a split zip file

If you want to split the zip file over several files when the size exceeds a particular limit, you can do so like this:

List<File> filesToAdd = Arrays.asList(
    new File("somefile"), 
    new File("someotherfile")
);

ZipFile zipFile = new ZipFile("filename.zip");
zipFile.createSplitZipFile(filesToAdd, new ZipParameters(), true, 10485760); // using 10MB in this example

Passing in new ZipParameters(), as in the above example, will make Zip4j use default zip parameters. Please look at ZipParameters to see the default configuration.

Zip file format specifies a minimum of 65536 bytes (64kb) as a minimum length for split files. Zip4j will throw an exception if anything less than this value is specified.

To create a split zip with password protection, pass in appropriate ZipParameters as shown in the example below:

ZipParameters zipParameters = new ZipParameters();
zipParameters.setEncryptFiles(true);
zipParameters.setEncryptionMethod(EncryptionMethod.AES);

List<File> filesToAdd = Arrays.asList(
    new File("somefile"), 
    new File("someotherfile")
);

ZipFile zipFile = new ZipFile("filename.zip", "password".toCharArray());
zipFile.createSplitZipFile(filesToAdd, zipParameters, true, 10485760); // using 10MB in this example

Zip64 format

Zip64 is a zip feature which allows support for zip files when the size of the zip file exceeds the maximum that can be stored in 4 bytes (i.e., greater than 4,294,967,295 bytes). Traditionally, zip headers have a provision of 4 bytes to store for file sizes. But with growing file sizes compared to a few decades back, zip file format extended support of file sizes which extends 4 bytes by adding additional headers which uses 8 bytes for file sizes (compressed and uncompressed file sizes). This feature is known as Zip64.

Zip4j will automatically make a zip file a Zip64 format and add appropriate headers, when it detects the zip file to be crossing this file size limit. You do not have to explicitly specify any flag for Zip4j to use this feature.

Extracting All files in a zip

new ZipFile("filename.zip").extractAll("/destination_directory");

Extracting All files in a password protected zip

new ZipFile("filename.zip", "password".toCharArray()).extractAll("/destination_directory");

Extracting a single file from zip

new ZipFile("filename.zip").extractFile("fileNameInZip.txt", "/destination_directory");

Extracting a single file from zip which is password protected

new ZipFile("filename.zip", "password".toCharArray()).extractFile("fileNameInZip.txt", "/destination_directory");

Extracting a single file from zip and giving it a new file name

Below example will extract the file fileNameInZip.txt from the zip file to the output directory /destination_directory and will give the file a name newfileName.txt. Without the third parameter of the new file name, the same name as the file in the zip will be used, which in this case is fileNameInZip.txt

new ZipFile("filename.zip", "password".toCharArray()).extractFile("fileNameInZip.txt", "/destination_directory", "newfileName.txt");

Get an input stream for an entry in a zip file

ZipFile zipFile = new ZipFile("filename.zip");
FileHeader fileHeader = zipFile.getFileHeader("entry_name_in_zip.txt");
InputStream inputStream = zipFile.getInputStream(fileHeader);

You can now use this input stream to read content from it/write content to an output stream. Please note that the entry/file name is relative to the directory it is in. If entry_name_in_zip.txt is in a folder called "root_folder" in the zip, then you can use zipFile.getFileHeader("root_folder/entry_name_in_zip.txt");

Remove a file/entry from a zip file

new ZipFile("filename.zip").removeFile("fileNameInZipToRemove");

Please note that the file name is relative the root folder in zip. That is, if the file you want to remove exists in a folder called "folder1", which in-turn exists in a folder called "root-folder", removing this file from zip can be done as below:

new ZipFile("filename.zip").removeFile("root-folder/folder1/fileNameInZipToRemove");

If you want to be sure that the file you want to remove exists in zip file or if you don't want to deal with file names as string when dealing removeFile api, you can use the other overloaded method which takes in a `FileHeader:

ZipFile zipFile = new ZipFile("someZip.zip");
FileHeader fileHeader = zipFile.getFileHeader("fileNameInZipToRemove");

if (fileHeader == null) {
  // file does not exist
}

zipFile.removeFile(fileHeader);

Merging split zip files into a single zip

This is the reverse of creating a split zip file, that is, this feature will merge a zip file which is split across several files into a single zip file

new ZipFile("split_zip_file.zip").mergeZipFile("merged_zip_file.zip");

This method will throw an exception if the split zip file (in this case split_zip_file.zip) is not a split zip file

List all files in a zip

List<FileHeader> fileHeaders = new ZipFile("zipfile.zip");
fileHeaders.stream().forEach(fileHeader -> System.out.println(fileHeader.getFileName()));

You can get all other information from the FileHeader object corresponding to each file/entry in the zip.

Check if a zip file is password protected

new ZipFile("encrypted_zip_file.zip").isEncrypted();

Check if a zip file is a split zip file

new ZipFile("split_zip_file.zip").isSplitArchive();

Set comment for a zip file

new ZipFile("some_zip_file.zip").setComment("Some comment");

Remove comment of a zip file

new ZipFile("some_zip_file.zip").setComment("");

Get comment of a zip file

new ZipFile("some_zip_file.zip").getComment();

Check if a zip file is valid

Note: This will only check for the validity of the headers and not the validity of each entry in the zip file.

new ZipFile("valid_zip_file.zip").isValid();

Working with streams

Adding entries with ZipOutputStream

import net.lingala.zip4j.AbstractIT;
import net.lingala.zip4j.exception.ZipException;
import net.lingala.zip4j.model.ZipParameters;
import net.lingala.zip4j.model.enums.AesKeyStrength;
import net.lingala.zip4j.model.enums.CompressionMethod;
import net.lingala.zip4j.model.enums.EncryptionMethod;
import org.junit.Test;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

public void zipOutputStreamExample(CompressionMethod compressionMethod, boolean encrypt,
                                   EncryptionMethod encryptionMethod, AesKeyStrength aesKeyStrength)
      throws IOException, ZipException {

    ZipParameters zipParameters = buildZipParameters(compressionMethod, encrypt, encryptionMethod, aesKeyStrength);
    byte[] buff = new byte[4096];
    int readLen;

    try(ZipOutputStream zos = initializeZipOutputStream(encrypt) {
      for (File fileToAdd : FILES_TO_ADD) {

        // Entry size has to be set if you want to add entries of STORE compression method (no compression)
        // This is not required for deflate compression
        if (zipParameters.getCompressionMethod() == CompressionMethod.STORE) {
          zipParameters.setEntrySize(fileToAdd.length());
        }

        zipParameters.setFileNameInZip(fileToAdd.getName());
        zos.putNextEntry(zipParameters);

        try(InputStream inputStream = new FileInputStream(fileToAdd)) {
          while ((readLen = inputStream.read(buff)) != -1) {
            zos.write(buff, 0, readLen);
          }
        }
        zos.closeEntry();
      }
    }
}

private ZipOutputStream initializeZipOutputStream(boolean encrypt) throws IOException {
    FileOutputStream fos = new FileOutputStream(generatedZipFile);

    if (encrypt) {
      return new ZipOutputStream(fos, PASSWORD);
    }

    return new ZipOutputStream(fos);
}

private ZipParameters buildZipParameters(CompressionMethod compressionMethod, boolean encrypt,
                                           EncryptionMethod encryptionMethod, AesKeyStrength aesKeyStrength) {
    ZipParameters zipParameters = new ZipParameters();
    zipParameters.setCompressionMethod(compressionMethod);
    zipParameters.setEncryptionMethod(encryptionMethod);
    zipParameters.setAesKeyStrength(aesKeyStrength);
    zipParameters.setEncryptFiles(encrypt);
    return zipParameters;
}

Extract files with ZipInputStream

import net.lingala.zip4j.ZipFile;
import net.lingala.zip4j.exception.ZipException;
import net.lingala.zip4j.model.LocalFileHeader;
import net.lingala.zip4j.model.ZipParameters;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public void extractWithInputStream(File zipFile, char[] password) throws IOException, ZipException {
    LocalFileHeader localFileHeader;
    int readLen;
    byte[] readBuffer = new byte[4096];

    try (FileInputStream fileInputStream = new FileInputStream(zipFile)) {
      try (ZipInputStream zipInputStream = new ZipInputStream(fileInputStream, password)) {
        while ((localFileHeader = zipInputStream.getNextEntry()) != null) {
          File extractedFile = new File(localFileHeader.getFileName());
          try (OutputStream outputStream = new FileOutputStream(extractedFile)) {
            while ((readLen = zipInputStream.read(readBuffer)) != -1) {
              outputStream.write(readBuffer, 0, readLen);
            }
          }
        }
      }
    }
}

Working with Progress Monitor

ProgressMonitor makes it easier for applications (especially user facing) to integrate Zip4j. It is useful to show progress (example: updating a progress bar, displaying the current action, show file name being worked on, etc). To use ProgressMonitor, you have to set ZipFile.setRunInThread(true). This will make any actions being done on the zip file to run in a background thread. You can then access ProgressMonitor Zipfile.getProgressMonitor() and get details of the current action being done along with the percentage work done, etc. Below is an example:

ZipFile zipFile = new ZipFile(generatedZipFile, PASSWORD);
ProgressMonitor progressMonitor = zipFile.getProgressMonitor();

zipFile.setRunInThread(true);
zipFile.addFolder("/some/folder");

while (!progressMonitor.getState().equals(ProgressMonitor.State.READY)) {
  Systetm.out.println("Percentage done: " + progressMonitor.getPercentDone());
  Systetm.out.println("Current file: " + progressMonitor.getFileName());
  Systetm.out.println("Current task: " + progressMonitor.getCurrentTask());
  
  Thread.sleep(100);
}

Note that in the above example, addFolder() will almost immediately return back the control to the caller. The client code can then perform a loop until the state gets back to "Ready" as shown in the above example.

Similarly, ProgressMonitor can be used with other actions like, addFiles, removeFiles and extractFiles.

Contribution

It is hard to find as much free time as I used to have when I first started Zip4j 10 years back in 2009. I would highly appreciate any support I can get for this project. You can fork this project, and send me pull requests for any bug fixes, issues mentioned here or new features. If you need any support in understanding the code or zip specification, just drop me a mail and I will help you as best as I can. (See FAQ for my email id.)

FAQ

  1. Why do I have to pass in password as char array and not as a string?

    That's why

  2. How can I contact you?

    srikanth.mailbox@gmail.com

  3. Are unicode file names supported?

    Yes, unicode file names (UTF-8) are supported as specified by the zip format specification. Zip4j will use utf-8 file name and file comment encoding when creating a zip file. When extracting a zip file, Zip4j will only use utf-8 encoding, only if the appropriate header flag is set as specified by zip file format specification. If this flag is not set, Zip4j will use Cp437 encoding which only supports English alphabetical characters.

  4. Where can I find Zip file format specification?

    Here

  5. Why are there so many changes in version 2.x compared to 1.x?

    Because 1.x was written about 10 years back, Zip4j was badly in need of a face-lift and code modernization. Also, my coding standards have also improved over the years (or at least that's what I like to think). Although I am proud of the work I did with Zip4j 10 years back, some parts of the code make me feel like hiding my face in shame. One such example is the usage of ArrayList instead of List. Api and code should look much neater now. And also, Zip4j now supports a minimum of JRE 8, as compared to JRE 5 with 1.x, which obviously will bring some nice features that I can make use of. (For example: no more explicitly closing the streams all over the code). If you still feel like something can be improved (and I am pretty sure that there are things to be improved), please let me know by opening an issue here or writing to me (My email id is in point #2 above).

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