This article is about how to write a utility class for extracting files and directories in a compressed zip archive, using built-in Java API.

The java.util.zip package provides the following classes for extracting files and directories from a ZIP archive:

    • ZipInputStream: this is the main class which can be used for reading zip file and extracting files and directories (entries) within the archive. Here are some important usages of this class:
      • read a zip via its constructor ZipInputStream(FileInputStream)
      • read entries of files and directories via method getNextEntry()
      • read binary data of current entry via method read(byte)
      • close current entry via method closeEntry()
      • close the zip file via method close()

       

    • ZipEntry: this class represents an entry in the zip file. Each file or directory is represented as a ZipEntry object. Its method getName() returns a String which represents path of the file/directory. The path is in the following form:

      folder_1/subfolder_1/subfolder_2/…/subfolder_n/file.ext

       

Based on the path of a ZipEntry, we re-create directory structure when extracting the zip file.

In addition, the BufferedOutputStream class is used to write content of the current ZipEntry to a file on disk, via its method write(byte[] bytes, int offset, int length).

Following is source code of UnzipUtility.java class:

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

/**
 * This utility extracts files and directories of a standard zip file to
 * a destination directory.
 * @author www.codejava.net
 *
 */
public class UnzipUtility {
    /**
     * Size of the buffer to read/write data
     */
    private static final int BUFFER_SIZE = 4096;
    /**
     * Extracts a zip file specified by the zipFilePath to a directory specified by
     * destDirectory (will be created if does not exists)
     * @param zipFilePath
     * @param destDirectory
     * @throws IOException
     */
    public void unzip(String zipFilePath, String destDirectory) throws IOException {
        File destDir = new File(destDirectory);
        if (!destDir.exists()) {
            destDir.mkdir();
        }
        ZipInputStream zipIn = new ZipInputStream(new FileInputStream(zipFilePath));
        ZipEntry entry = zipIn.getNextEntry();
        // iterates over entries in the zip file
        while (entry != null) {
            String filePath = destDirectory + File.separator + entry.getName();
            if (!entry.isDirectory()) {
                // if the entry is a file, extracts it
                extractFile(zipIn, filePath);
            } else {
                // if the entry is a directory, make the directory
                File dir = new File(filePath);
                dir.mkdir();
            }
            zipIn.closeEntry();
            entry = zipIn.getNextEntry();
        }
        zipIn.close();
    }
    /**
     * Extracts a zip entry (file entry)
     * @param zipIn
     * @param filePath
     * @throws IOException
     */
    private void extractFile(ZipInputStream zipIn, String filePath) throws IOException {
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(filePath));
        byte[] bytesIn = new byte[BUFFER_SIZE];
        int read = 0;
        while ((read = zipIn.read(bytesIn)) != -1) {
            bos.write(bytesIn, 0, read);
        }
        bos.close();
    }
}

 

The UnzipUtility class has a public method for extracting files and directories from a zip archive:

    •           unzip(String zipFilePath, String destDirectory): extracts content of a zip file specified by zipFilePath to a directory specified by destDirectory.

 

 

And source code of a test class, UnzipUtilityTest.java:

/**
 
* A console application that tests the UnzipUtility class
 *
 * @author www.codejava.net
 *
 */
public class UnzipUtilityTest {
    public static void main(String[] args) {
        String zipFilePath = "e:/Test/MyPics.zip";
        String destDirectory = "f:/Pics";
        UnzipUtility unzipper = new UnzipUtility();
        try {
            unzipper.unzip(zipFilePath, destDirectory);
        } catch (Exception ex) {
            // some errors occurred
            ex.printStackTrace();
        }
    }
}

 

Recommended Book: Java I/O

Attachments:
Download this file (UnzipUtility.java)UnzipUtility.java[utility class]1 kB
Download this file (UnzipUtilityTest.java)UnzipUtilityTest.java[test class]0.4 kB
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