The given code creates a jar file using java.

import java.io.*;
import java.util.jar.*;

public class CreateJar {
  public static int buffer = 10240;
  protected void createJarArchive(File jarFile, File[] listFiles) {
    try {
      byte b[] = new byte[buffer];
      FileOutputStream fout = new FileOutputStream(jarFile);
      JarOutputStream out = new JarOutputStream(fout, new Manifest());
      for (int i = 0; i < listFiles.length; i++) {
        if (listFiles[i] == null || !listFiles[i].exists()|| listFiles[i].isDirectory())
      System.out.println();
        JarEntry addFiles = new JarEntry(listFiles[i].getName());
        addFiles.setTime(listFiles[i].lastModified());
        out.putNextEntry(addFiles);

        FileInputStream fin = new FileInputStream(listFiles[i]);
        while (true) {
          int len = fin.read(b, 0, b.length);
          if (len <= 0)
            break;
          out.write(b, 0, len);
        }
        fin.close();
      }
      out.close();
      fout.close();
      System.out.println("Jar File is created successfully.");
    } catch (Exception ex) {}
  }
  public static void main(String[]args){
    CreateJar jar=new CreateJar();
    File folder = new File("C://Answers//Examples");
      File[] files = folder.listFiles();
    File file=new File("C://Answers//Examples//Examples.jar");
    jar.createJarArchive(file, files);
  }
}