How to Unzip in Java

Here is a quick java program to unzip or explode a zip file. We will read the zip file with the help of java.util.ZipFile, then we will process each entries inside this. We will read the entries as stream and write to a buffer and eventually to a file output stream.  So at the end we will extract all the elements in the zip, and maintain the same hierarchical structure of directories .Please refer the below example.

	import java.io.File;
	import java.io.FileOutputStream;
	import java.io.IOException;
	import java.io.InputStream;
	import java.util.Enumeration;
	import java.util.zip.ZipEntry;
	import java.util.zip.ZipFile;
	public class UnZipDemo {
	public static void main(String args[]) throws IOException
	{
	String zipFileName = "D:\\demo.zip";
	ZipFile zipFile = new ZipFile(zipFileName);
	String extractedPath = "D:\\demo";
	byte[] buffer = new byte[1024];
	Enumeration enm = zipFile.entries();
	ZipEntry ze = null;
	InputStream fis = null;
	while (enm.hasMoreElements()) {
	ze = (ZipEntry) enm.nextElement();
	System.out.println("processing = "+ze.getName());
	File newFile = new File(extractedPath + File.separator + ze.getName());
	// create all non exists folders
	new File(newFile.getParent()).mkdirs();
	FileOutputStream fos = new FileOutputStream(newFile);
	int len;
	fis = zipFile.getInputStream(ze);
	while ((len = fis.read(buffer)) > 0) {
	fos.write(buffer, 0, len);
	}
	fos.close();
	fis.close();
	}
	}
	}

Zip files in Java

To create or read zip files in Java, we can use java.util.ZipFile. This allow to read an zip file and read the entries inside it. We can create a zip file by using ZipOutputStream.

Please refer the below example program

https://github.com/pallabrath/myexpjava/blob/master/myexpjava/src/demo/zipfile/ZipFileDemo.java

package demo.zipfile;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.util.Enumeration;

import java.util.Scanner;

import java.util.zip.ZipEntry;

import java.util.zip.ZipFile;

import java.util.zip.ZipOutputStream;

public class ZipFileDemo {

public static void main(String args[]) throws IOException {

// create a zip file

String zipFileName = "D:\\demo.zip";

ZipOutputStream zipos = new ZipOutputStream(new FileOutputStream(zipFileName));

// In Zip Output Stream we can create file.

ZipEntry ze1 = new ZipEntry("file1.txt");

zipos.putNextEntry(ze1);

zipos.write("Hello World".getBytes());

zipos.closeEntry();

// Now lets create another file in a directory

zipos.putNextEntry(new ZipEntry("etc\\file2.txt"));

zipos.write("Hello Again".getBytes());

zipos.closeEntry();

zipos.close();

// To Read Zip file

ZipFile zipFile = new ZipFile(zipFileName);

// for specific entry

ZipEntry ze2 = zipFile.getEntry("file1.txt");

InputStream is = zipFile.getInputStream(ze2);

Scanner scan = new Scanner(is);

while (scan.hasNextLine()){

System.out.println(scan.nextLine());

}

scan.close();

Enumeration enm = zipFile.entries();

while(enm.hasMoreElements()) {

ZipEntry ze = (ZipEntry) enm.nextElement();

System.out.println(ze.getName());

}

}

}

Java 8 at a glance

In Java  8 following are the major enhancement.

- Lambda Expression
- Method Reference for Lambda Expression
- Java Streams
- Improved Interface

    a) Now we can have concrete methods in an interface. It can be either static or default. Default methods can be overridden in implemented class. If a class implement two or more interface and there is a collision of default method then it is mandatory to override.
    b) Functional interface. For lambda expression we can define an interface as function it will have only one abstract method.
Here is an good article explaining in details # https://www.journaldev.com/2752/java-8-interface-changes-static-method-default-method

- Enhancement to Annotation
More details # https://www.javatpoint.com/java-8-type-annotations-and-repeating-annotations

- Parallel Array Sorting
    java.util.Arrays support sorting in parallel which will be faster.
- Hash Map performance improvement in case of Key collision
- Removed JDBC-ODBC bridge


More details on Java 8 features
http://www.oracle.com/technetwork/java/javase/8-whats-new-2157071.html