Badpaddingexception while decrypting

hai all
               i am doing a project in secured data transmission using core java, socket programming and cryptography.my program works on client side and server side. My problem is that i could encrypt the text successfully but i couldn't decrypt. when i try to decrypt i am getting an exception 'BadPaddingException' which i couldn't solve. in generating the encryption or decryption code i used DES encryption algorithm provided by JCE. in the program i used i/o streams and swings. here i am giving the entire coding of my program. plz help me out to solve this

import java.io.*;
import java.awt.*;
import java.text.*;
import java.lang.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import javax.crypto.*;
import java.security.*;
import java.security.interfaces.*;
import java.util.*;
import com.sun.crypto.provider.SunJCE.*;
class server extends JFrame implements ActionListener,Runnable
{
      Thread t;
      JFileChooser fc;
      JTextField jtf;
      JTextArea data;
      JLabel title;
      JFrame f;
      JButton open,receive,send,exit,encrypt,decrypt;
      Socket s;
      ServerSocket ss;
      JComboBox jcb;
      PrintStream ps;
      InputStreamReader j;
      BufferedReader br;
      public server()
      {
        t=new Thread(this,"RECEIVE");
            System.out.println("child Thread:"+t);
            t.start();
            JPanel p1=new JPanel(new FlowLayout());
            JPanel p2=new JPanel(new FlowLayout());
            JPanel p3=new JPanel(new FlowLayout());
            jtf=new JTextField(15);
            data=new JTextArea(100,30);
            title=new JLabel("SERVER IP");
            String[] item={"192.168.3.189"};
            jcb=new JComboBox(item);
            open=new JButton("OPEN");
            send=new JButton("SEND");
            exit=new JButton("EXIT");
            encrypt=new JButton("ENCRYPT");
            decrypt=new JButton("DECRYPT");
            p1.add(title);
            p1.add(jtf);
            p1.add(jcb);
            p2.add(data);
            p3.add(open);
            p3.add(send);
            p3.add(encrypt);
            p3.add(decrypt);
            p3.add(exit);
            int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
            int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
            JScrollPane jsp=new JScrollPane(p2,v,h);
            jsp.setViewportView(data);
            getContentPane().add(p1,BorderLayout.NORTH);
            getContentPane().add(p2,BorderLayout.CENTER);
            getContentPane().add(p3,BorderLayout.SOUTH);
            getContentPane().add(jsp,BorderLayout.CENTER);
            open.addActionListener(this);
            send.addActionListener(this);
            encrypt.addActionListener(this);
            decrypt.addActionListener(this);
            exit.addActionListener(this);
            setSize(400,400);
            show();

      }
      public void run()
      {
            try
            {
                  if(ss==null)
                  {
                        ss=new ServerSocket(2018);
                        s=ss.accept();
                        ps=new PrintStream(s.getOutputStream(),true);
                        j=new InputStreamReader(s.getInputStream());
                        br=new BufferedReader(j);
                        System.out.println("socket created");
           }
           while(true)
           {
                     //data.setText(" ");
                     String s4;
                     while((s4=br.readLine())!=null&& !(s4.equals("eof")))
                           {
                                 System.out.println("inside while");
                                 data.append(s4);
                                 data.append("\n");
                          //System.out.println(s4);

                        }
                Thread.sleep(100);
               }
    }
             catch(Exception e)
             {
                   System.out.println("Exception"+e);
               }

       }

      public void actionPerformed(ActionEvent ae)
      {
            String msg=ae.getActionCommand();
            try
            {
              if(msg.equals("SEND"))
                  {
                        jtf.setText(msg);
                        String s3=data.getText();
                        ps.println(s3);
                        ps.println("eof");

                  }
              if(msg.equals("OPEN"))
                  {
                        System.out.println("inside open");
                        fc=new JFileChooser();
                        int get=fc.showOpenDialog(f);
                        File file=fc.getSelectedFile();
                        String s2=file.toString();
                        FileReader fr=new FileReader(s2);
                        BufferedReader ds=new BufferedReader(fr);
                        String s1="";
                        data.setText("");
                        while((s1=ds.readLine())!=null)
                        {
                              data.append(s1);
                              data.append("\n");
                        }
                        jtf.setText(msg);
                        System.out.println("open completed");

                  }

                  jtf.setText(msg);
        if(msg.equals("ENCRYPT"))
                  {
                        SecretKey key=KeyGenerator.getInstance("DES").generateKey();
                        Cipher ec=Cipher.getInstance("DES");
                        ec.init(Cipher.ENCRYPT_MODE,key);
                        String str=data.getText();
                        byte[] b1=str.getBytes("UTF8");
                        byte[] b2=ec.doFinal(b1);
                        String encodedString=new sun.misc.BASE64Encoder().encode(b2);
                        data.setText(encodedString);
                  }
            if(msg.equals("DECRYPT"))
                  {

                    SecretKey key=KeyGenerator.getInstance("DES").generateKey();
                              Cipher dc=Cipher.getInstance("DES");
                              dc.init(Cipher.DECRYPT_MODE,key);
                              String st=data.getText();
                              byte[] b3=new sun.misc.BASE64Decoder().decodeBuffer(st);
                    //System.out.println(b3);
                    byte[] b4=dc.doFinal(b3);
                              System.out.println("inside decrypt");
                              System.out.println(b4);
                              String ca=new String(b4,"UTF8");
                              System.out.println(ca);
                          data.setText(ca);
                  }

        if(msg.equals("EXIT"))
                  {
                        jtf.setText(msg);
                        ps.close();
                        s.close();
                        ss.close();
                        System.exit(0);
                  }

            }
            catch(FileNotFoundException e)
             {
                  System.out.println("File not found"+e);
             }
          catch(UnknownHostException e)
             {
               System.out.println("unknown host"+e);
             }
            catch(IOException e)
            {
              System.out.println("I/O Exception"+e);
          }
        catch(Exception e)
             {
                   e.printStackTrace();
                   System.out.println("Exception"+e);
             }

      }
}
public class ctserver
{
      public static void main(String args[])throws Exception
      {
            new server();
      }
}