I want to make a chat application in java but when I'm trying to log in to the server it gives me an error or it has unending loop. I cant find the error.

when I try to log in to the server using the client. the while loop in checkClientMessage() method doesnt stop
it gives me unending loop like "User "+loginUser[0] +" has logged in" as a message.
also, it should print "200" when the user can log in, but in the client side, it cannot read "200" and it doesnt read anything. it prints out null string.
please help me. here are my codes.

//This is the chat server application
Code:
package chatfiles;

import java.io.*;
import java.net.*;
import java.util.*;
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class ChatServer {
	private JFrame jframe;
	private Container container;
	private JButton jb1;
	private JTextField jtf1;
	private JTextField jtf2;
	private JLabel jl1;
	
	private ServerSocket serverSocket = null;
	private static Socket socket = null;
    public static void main(String[] args){
    	/*try{
    		ServerSocket ss = new ServerSocket(1234);
    		System.out.println("Server is running on port: "+ss.getLocalPort());
    		while(true){
    			new serverOn(ss.accept()).start();
    		}
    		
    	}catch(Exception e){
    		System.out.println("error here serverSocket)");
    	}*/
    	
    	new ChatServer();
    }
    
    public void stopServer(){
    	try{
    		serverSocket.close();
    		socket.close();
    		jb1.setText("Start Server");
    		jtf1.setEnabled(true);
    		jtf1.setText("");
    		jl1.setText("");
    		
    	}catch(Exception e){
    		System.err.println("error on closing sockets: "+e);
    		JOptionPane.showMessageDialog(jframe,"cannot close ServerSocket");
    	}
    }
    
    public void startServer(int port){
    	try{
    		serverSocket = new ServerSocket(port);
    		jl1.setText("server is running on port: "+String.valueOf(port));
    		jb1.setText("Stop Server");
    		jtf1.setEnabled(false);
    		try{
    			while(true){
    				try{
    					socket = serverSocket.accept();
    					new serverOn(socket).start();
    					jtf2.setText(jtf2.getText().toString() + "a client has connected: \n");
    				}catch(Exception b){
    					System.err.println("error when client is connecting INSIDE while(true): "+b);
    					JOptionPane.showMessageDialog(jframe,"error when client is connecting INSIDE while(true) on port: "+port);
    				}
    			}
    		}catch(Exception a){
    			System.err.println("error when client is connecting OUTSIDE while(true): "+a);
    			JOptionPane.showMessageDialog(jframe,"error when client is connecting OUTSIDE while(true) on port: "+port);
    		}
    	}catch(Exception e){
    		System.err.println("error on starting server: "+e);
    		JOptionPane.showMessageDialog(jframe,"cannot start ServerSocket on port: "+port);
    	}
    }
    
    public ChatServer(){
    	jframe = new JFrame("Chat Server Frame");
    	jframe.setSize(500,300);
    	jframe.setDefaultCloseOperation(jframe.EXIT_ON_CLOSE);
    	
    	container = jframe.getContentPane();
    	container.setLayout(new GridLayout(2,2));
    	
    	jb1 = new JButton("Start Server");
    	
    	jtf1 = new JTextField();
    	jtf2 = new JTextField();
    	
    	jl1 = new JLabel();
    	
    	container.add(jb1);
    	container.add(jtf1);
    	container.add(jl1);
    	container.add(jtf2);
    	
    	jb1.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			try{
    				if(jtf1.getText().toString()!=null){
    					try{
    						Thread t = new Thread(){
    							public void run(){
    								try{
    									if(jb1.getText().toString().equals("Start Server")){
    										if(jtf1.getText().toString().length() > 3 && jtf1.getText().toString().length() < 6){
    											startServer(Integer.parseInt(jtf1.getText().toString()));
    										}else{
    											JOptionPane.showMessageDialog(jframe,"input port > 1024 && port < 60000");
    										}
    										
    									}else{
    										stopServer();
    									}
    								}catch(Exception aea){
    								}
    							}
    						};
    						t.start();
    					}catch(Exception ea){
    						JOptionPane.showMessageDialog(jframe,"Inside Thread Error()");
    					}
    				}else{
    					JOptionPane.showMessageDialog(jframe,"Input a port number");
    				}
    			}catch(Exception a){
    				JOptionPane.showMessageDialog(jframe,"Input a valid number");
    			}
    		}
    	});
    	
    	
    	jframe.setVisible(true);
    }
}

class serverOn extends Thread{
	private Socket socket = null;
	
	private boolean checker = false;
	private static Hashtable<String, serverOn> hashtable = new Hashtable<String, serverOn>();
	private JFrame jframe = new JFrame();
	
	private BufferedReader br;
	private PrintWriter pw;
	
	public serverOn(Socket s){
		socket = s;
		try{
			br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
			pw = new PrintWriter(socket.getOutputStream(),true);
			
		}catch(Exception e){
			System.out.println("error here serverOn()");
		}
		
	}
	public void run(){
			try{
				String line;
					while((line = br.readLine())!=null){
					System.out.println("message: "+line);
					checkClientMessage(line);
					}
			}catch(Exception e){
				System.err.println("error run()"+e);
			}
	}
	
	public void checkClientMessage(String line){
		try{
				String name = "";
					while(!line.equals("exit")){
						try{
						String lineTemp[] = line.split(" ");
							if(lineTemp[0].equals("login")){
								String temp[] = line.split(" ");
								String loginUser[] = temp[1].split(",");
								checkUser(loginUser[0],loginUser[1]);
								if(checker){
									hashtable.put(loginUser[0],this);
									pw.println("200");
									System.out.println("User "+loginUser[0] +" has logged in.\n");
									checker = false;
								}else{
									pw.println("400");
								}
							}
							if(lineTemp[0].equals("reg")){
								String temp[] = line.split(" ");
								String registerUser[] = temp[1].split(",");
								regUser(registerUser[0],registerUser[1]);
								if(checker){
									hashtable.put(registerUser[0],this);
									System.out.println("User "+registerUser[0] +" registered.\n");
									checker = false;
								}
							}
							if(lineTemp[0].equals("/pm")){
								String PMline[] = line.split(" ");
								String PMmsg ="";
								for(int i = 2; i<PMline.length; i++){
									PMmsg += PMline[i] +" ";
								}
								hashtable.get(PMline[1]).privateMessage(name, PMmsg.trim());
								System.out.println(name + " pm'ed " + PMline[1] + "message: "+PMmsg.trim());
								
							}else if(lineTemp[0].equals("/bmsg")){
								String BMline[] = line.split(" ");
								String BMmsg = "";
								for(int i = 2; i<BMline.length; i++){
									BMmsg += BMline[i] + " ";
								}
								for(serverOn so : hashtable.values()){
									so.broadcastMessage(name,BMmsg.trim());
									System.out.println(name + " broadcast message:  "+BMmsg.trim());
								}
							}
						}catch(Exception e){
							if(!line.equals("exit")){
								System.out.println("error here RUN()");
								JOptionPane.showMessageDialog(jframe,"Error here RUN()");
							}
						}
					}
			}catch(Exception ee){
			}
	}
	
	public void checkUser(String user, String pass) throws Exception{
		BufferedReader br = new BufferedReader(new FileReader("users.txt"));
		String line = "";
		while((line = br.readLine())!=null){
			String temp[] = line.split(",");
			if(temp[0].equals(user)){
				if(temp[1].equals(pass)){
					pw.println("200");
					checker = true;
					br.close();
					break;
				}else{
					pw.write("400");
				}
			}
		}
	}
	
	public void privateMessage(String name, String message){
		try{
			pw.println("[PrivateMessage]"+name+":"+message+"\n");
		}catch(Exception e){
			System.out.println("pm message error: "+e);
		}
	}
	
	public void broadcastMessage(String name, String message){
		try{
			pw.println(name + ":" + message + "\n");
		}catch(Exception e){
			System.out.println("broadcast message error: "+e);
		}
	}
	
	public void regUser(String user, String pass) throws Exception{
		BufferedWriter bw = new BufferedWriter(new FileWriter("users.txt"));
		bw.write(user+","+pass);
		checker = true;
		pw.write("200");
		bw.flush();
		bw.close();
	}
}


//this is the chat client application
Code:
package chatfiles;

import java.net.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class ChatClient extends Thread{
	private JFrame jframe;
	private Container container;
	private JButton jb1,jb2,jb3,jb4;
	private JTextField jtf1,jtf2,jtf3;
	private JLabel jl1,jl2,jl3;
	
	private static Socket socket;
	
	private BufferedReader br;
	private PrintWriter pw;
	
	private String messageFromServer = "";
	private String msgTemp = "";
	
	private boolean connectorChecker = false;
	private boolean responseChecker = false;
	
    public static void main(String[] args) {
    	
    	new ChatClient(socket).start();
    } 
    
    public void run(){
    	try{
    		while(msgTemp != null){
    			msgTemp = br.readLine();
    			messageFromServer = msgTemp;
    			System.out.println(msgTemp);
    			JOptionPane.showMessageDialog(jframe,"MESSAGE FROM SERVER: "+msgTemp);
    			}
    	}catch(Exception e){
    		JOptionPane.showMessageDialog(jframe,"error run CHATCLIENT()");
    	}
    }	
    	
    public ChatClient(Socket sock){
    	jframe = new JFrame("Welcome Frame");
    	jframe.setSize(300,400);
    	jframe.setDefaultCloseOperation(jframe.EXIT_ON_CLOSE);
    	
    	container = jframe.getContentPane();
    	container.setLayout(new GridLayout(5,2));
    	
    	jb1 = new JButton("Login");
    	jb2 = new JButton("Register");
    	jb3 = new JButton("Connect to server");
    	jb4 = new JButton("Exit");
    	
    	jtf1 = new JTextField("");
    	jtf1.setText("");
    	jtf2 = new JTextField("");
    	jtf2.setText("");
    	jtf3 = new JTextField("");
    	jtf3.setText("");
    	
    	jl1 = new JLabel("username:");
    	jl2 = new JLabel("password:");
    	
    	container.add(jl1);
    	container.add(jtf1);
    	container.add(jl2);
    	container.add(jtf2);
    	container.add(jb1);
    	container.add(jb2);
    	container.add(jtf3);
    	container.add(jb3);
    	container.add(jb4);
    	
    	jb3.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			try{
    				connectToServer(jtf3.getText().toString());
    				if(connectorChecker){
    					jb3.setEnabled(false);
    					jtf3.setEnabled(false);
    					jb3.setText("connected");
    				}
    			}catch(Exception a){
    				System.err.println("JBUTTON 3 ERROR: "+a);
    			}
    		}
    	});
    	
    	jb1.addActionListener(new ActionListener(){
				public void actionPerformed(ActionEvent e){
					Thread t = new Thread(){
						public void run(){
							try{
		    				pw.println("login "+jtf1.getText().toString()+","+jtf2.getText().toString());
		    				
		    				checkResponse(messageFromServer);
		    				
			    			}catch(Exception a){
			    				System.err.println("JButton 2 login error: "+a);
			    			}
						}
					};
					t.start();
    			}
    		});
    		
    	jb2.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			try{
    				jframe.setVisible(false);
    				new ChatRegister(socket);
    			}catch(Exception a){
    				System.err.println("error in register: "+e);
    			}
    		}
    	});
    	
    	jb4.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			try{
    				pw.close();
    				br.close();
    				socket.close();
    				System.exit(0);
    			}catch(Exception a){
    				JOptionPane.showMessageDialog(jframe,"error sa exit");
    			}
    		}
    	});
    	jframe.setVisible(true);
    	
    }
    
    public void checkResponse(String line){
    	try{
    		if(line.equals("200")){
    			JOptionPane.showMessageDialog(jframe,"sucessfully logged in");
    			connectorChecker = true;
    		}else if(line.equals("400")){
    			JOptionPane.showMessageDialog(jframe,"wrong username / password");
    			connectorChecker = false;
    		}else{
    			JOptionPane.showMessageDialog(jframe,"wrong output from server");
    			JOptionPane.showMessageDialog(jframe,line);
    			connectorChecker = false;
    		}
    	}catch(Exception e){
    		JOptionPane.showMessageDialog(jframe,"checkResponse() error");
    	}
    }
    
    public void connectToServer(String port){
    	try{
    		int a = Integer.parseInt(port);
    		socket = new Socket("localhost",a);
    		
    		br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
			pw = new PrintWriter(socket.getOutputStream(),true);
			
    		connectorChecker = true;
    	}catch(Exception e){
    		System.err.println("connect to server error: "+e);
    	}
    }
    
    public void closeConnection(){
    	try{
    		socket.close();
    		br.close();
    		pw.close();
    	}catch(Exception e){
    		System.err.println("error in closing connection."+e);
    	}
    }
     
}

class ChatRegister{
	private JFrame jframe;
	private Container container;
	private JLabel jl1,jl2,jl3;
	private JButton jb1,jb2;
	private JTextField jtf1,jtf2,jtf3;
	public ChatRegister(final Socket socket){
		jframe = new JFrame("Chat Register Frame");
		jframe.setSize(300,400);
		jframe.setDefaultCloseOperation(jframe.EXIT_ON_CLOSE);
		
		container = jframe.getContentPane();
		container.setLayout(new GridLayout(4,2));
		
		jl1 = new JLabel("username:");
		jl2 = new JLabel("password:");
		jl3 = new JLabel("re-type password:");
		
		jb1 = new JButton("Register");
		jb2 = new JButton("Clear");
		
		jtf1 = new JTextField("");
		jtf2 = new JTextField("");
		jtf3 = new JTextField("");
		
		container.add(jl1);
		container.add(jtf1);
		container.add(jl2);
		container.add(jtf2);
		container.add(jl3);
		container.add(jtf3);
		container.add(jb1);
		container.add(jb2);
		
		jb1.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e){
				try{
					if(jtf2.getText().toString().equals(jtf3.getText().toString())){
						if(jtf2.getText().toString().length() > 5 && jtf2.getText().toString().length() < 15){
							//dos.writeChars("reg "+jtf1.getText().toString()+","+jtf2.getText().toString());
							JOptionPane.showConfirmDialog(jframe,"Successfuly registered! Select OK to procceed");
							jframe.setVisible(false);
							new ChatClient(socket);
						}else{
							JOptionPane.showMessageDialog(jframe,"passwords should be greater than 5 and less than 15 characters.");
						}
					}else{
						JOptionPane.showMessageDialog(jframe,"passwords are not equal.");
					}
				}catch(Exception a){
					System.err.println("error on register button"+a);
				}
			}
		});
		
		jb2.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e){
				try{
					jtf1.setText("");
					jtf2.setText("");
					jtf3.setText("");
				}catch(Exception a){
					System.err.println("error in clear text register: "+a);
				}
			}
		});
		jframe.setVisible(true);
	}
}

class ClientFrame{
	
}
please help me. thank you for your help