Program: How to generate checksum value for for a file in java?

A Checksum is used for error checking or to identify whether the file is corrupted while transferring a file in the network. The data transfer happens in the form of packets. Checksum is computed on the contents of a file. For each packet the computed checksum value will be different. This computed value is transmitted along with the packet. At the receiving end we verify the checksum values to determine whether the file is corrupted or not. Below example shows how to generate checksum value.

package com.java2novice.zip;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.Adler32;
import java.util.zip.CheckedInputStream;
import java.util.zip.CheckedOutputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;

public class MyChecksumExample {

	public static void main(String a[]){
		
		//Create a zip file using checksum
		MyChecksumZip mfe = new MyChecksumZip();
		List<String> files = new ArrayList<String>();
		files.add("C:/test.txt");
		files.add("C:/test.sh");
		files.add("C:/port-chn.txt");
		mfe.zipFiles(files);
		//Unzip the file using checksum 
		MyChecksumUnzip mcu = new MyChecksumUnzip();
		mcu.unzipFile("C:/testing.zip");
	}
}

class MyChecksumZip{
	
	public void zipFiles(List<String> files){
		
		FileOutputStream fos = null;
        ZipOutputStream zipOut = null;
        FileInputStream fis = null;
        CheckedOutputStream checksumOs = null;
		try {
			fos = new FileOutputStream("C:/testing.zip");
			checksumOs = new CheckedOutputStream(fos, new Adler32());
			zipOut = new ZipOutputStream(new BufferedOutputStream(checksumOs));
			for(String filePath:files){
				File input = new File(filePath);
				fis = new FileInputStream(input);
				ZipEntry ze = new ZipEntry(input.getName());
				System.out.println("Zipping the file: "+input.getName());
				zipOut.putNextEntry(ze);
				byte[] tmp = new byte[4*1024];
				int size = 0;
				while((size = fis.read(tmp)) != -1){
					zipOut.write(tmp, 0, size);
				}
				zipOut.flush();
				fis.close();
			}
			zipOut.close();
			System.out.println("checksum: "+checksumOs.getChecksum().getValue());
			System.out.println("Done... Zipped the files...");
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally{
			try{
				if(fos != null) fos.close();
			} catch(Exception ex){
				
			}
		}
	}
}

class MyChecksumUnzip{
	
	public void unzipFile(String filePath){
		
		FileInputStream fis = null;
		ZipInputStream zipIs = null;
		ZipEntry zEntry = null;
		try {
			fis = new FileInputStream(filePath);
			CheckedInputStream checksumIs = new CheckedInputStream(fis, new Adler32());
			zipIs = new ZipInputStream(new BufferedInputStream(checksumIs));
			while((zEntry = zipIs.getNextEntry()) != null){
				try{
					byte[] tmp = new byte[4*1024];
					FileOutputStream fos = null;
					String opFilePath = "C:/"+zEntry.getName();
					System.out.println("Extracting file to "+opFilePath);
					fos = new FileOutputStream(opFilePath);
					int size = 0;
					while((size = zipIs.read(tmp)) != -1){
						fos.write(tmp, 0 , size);
					}
					fos.flush();
					fos.close();
				} catch(Exception ex){
					
				}
			}
			zipIs.close();
			System.out.println("Checksum: "+checksumIs.getChecksum().getValue());
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

Zipping the file: test.txt
Zipping the file: test.sh
Zipping the file: port-chn.txt
checksum: 108027849
Done... Zipped the files...
Extracting file to C:/test.txt
Extracting file to C:/test.sh
Extracting file to C:/port-chn.txt
Checksum: 108027849