Zip Files in Java Using java.util.zip Package

by
Java provides the ‘java.util.zip’ package to compress and decompress the data. To get started, we will need to import the necessary classes from the java.util.zip package. These classes allow us to work with zip files and compress data.

In the below example we are using ZipOutputStream and  ZipEntry Class. Both are essential classes in Java’s java.util.zip package for working with ZIP files. They play crucial roles in creating and manipulating ZIP archives.

ZipOutputStream:

  • Purpose: ZipOutputStream is a class that provides the functionality to write data to a ZIP file in a compressed format.
  • Usage: You use ZipOutputStream to create a new ZIP file or update an existing one by adding entries (files or directories) and their compressed data.
  • Key Methods:
    • putNextEntry(ZipEntry e): Starts a new ZIP entry (file or directory) within the archive.
    • write(byte[] buffer, int offset, int length): Writes compressed data to the current ZIP entry.
    • closeEntry(): Closes the current ZIP entry.
    • close(): Closes the ZipOutputStream.

ZipEntry:

  • Purpose: ZipEntry represents an entry (file or directory) within a ZIP file. It holds information about the entry, such as its name, size, and compression settings.
  • Usage: You create a ZipEntry object for each file or directory you want to include in the ZIP archive.
  • Key Methods and Properties:
    • setName(String name): Sets the name of the ZIP entry.
    • getSize(): Returns the uncompressed size of the entry.
    • setCompressedSize(long csize): Sets the compressed size of the entry.
    • setMethod(int method): Sets the compression method (typically DEFLATE).

Together, ZipOutputStream and ZipEntry allow you to create, update, and manage ZIP files in your Java applications. You can add files, specify their compression settings, and write compressed data to the ZIP archive using these classes

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

public class ZipFilesExample {
    public static void main(String[] args) {
        String[] sourceFiles = {"c:\\file1.txt", "c:\\file2.txt"};
        String zipFileName = "c:\\documents\\output.zip";

        try {
            FileOutputStream fos = new FileOutputStream(zipFileName);
            ZipOutputStream zipOut = new ZipOutputStream(fos);

            for (String sourceFile : sourceFiles) {
                File fileToZip = new File(sourceFile);
                
                FileInputStream fis = new FileInputStream(fileToZip);

                ZipEntry zipEntry = new ZipEntry(fileToZip.getName());
                zipOut.putNextEntry(zipEntry);

                byte[] bytes = new byte[1024];
                int length;
                while ((length = fis.read(bytes)) >= 0) {
                    zipOut.write(bytes, 0, length);
                }

                fis.close();
                zipOut.closeEntry();
            }

            zipOut.close();

            System.out.println("Files have been zipped successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

 

Let’s break down the code step by step:

1. We define an array of source files (sourceFiles) and specify the name and location of the output zip file (zipFileName).

2. We start by creating an output stream (fos) to write to the zip file. The ZipOutputStream (zipOut) is responsible for handling the zip entries.

3. We iterate through each source file in the sourceFiles array. For each file, we create a File object (fileToZip) and a FileInputStream (fis). Then, we create a ZipEntry for the file and add it to the ZipOutputStream.

4. Inside the loop, we read the file’s content in chunks and write it to the zip stream. Once the file is fully processed, we close the input stream (fis) and the zip entry.

5. Finally, we close the zip output stream (zipOut) and print a success message.

The package java.util.zip in Java  is all about running with ZIP and GZIP files. It allows you read and write them. it may additionally compress and decompress records using the DEFLATE technique, which each ZIP and GZIP formats use. Plus, it provides utility classes to calculate checksums (CRC-32 and Adler-32) of arbitrary input streams.
 Read more:- java.util.zip package summary

Leave a Comment