client hangs after getting data from server

[mihir maniar]

i have designed a client server architecture where in the client asks the server to authenticate and allow hime to chat. the client hangs when the login button is pressed. the server authenticates him properly and it informs the client that he is valid .
the code of client to server for authentication is

clientbfw.write(username+"\n");
clientbfw.flush();

on the server side the server authenticates him and notifies him that he is authenticated or not and the client does get the info in the following way

while((temp==bfr.readLine())!=null)
{
System.out.println(temp);
}

the client prints the information from the server but then it just hangs. what is wrong that i am doing .please guide me...

[Ko Ko Naing]

Is there any exception that the client throws? If not, it is alright with your code. I think you just need to close the application peacefully, after the client got the response from the server.

Or your code must be inside while(true) loop so that you can chat with the server back and forth, sending the requests and responses... This is called blocking approach in client-server chat application...

There also is non-blocking approach, which is discussed in the "Java Network Programming, Third Edition" from Manning Publishing... You might want to have a look at that too...

Hope it helps...

[mihir maniar]

i want a back and forth talk between the client and the server and when they are done talkin then the client can inform the server that he wants to log out and that is when i want to close the socket.so how should i do that?

[Elliotte Rusty Harold]

There are several things that could go wrong here. It's hard to tell without seeing the complete code. However, one thing does jump out at me: readLine(). Never, never, never use this method. It is dangerous and evil; and causes exactly the problem you're seeing. I can't be sure that's the problem here, but I wouldn't even bother trying anything else until you removed that from your code.

If you do need readLine-like funcitonality then you should reinvent it on top of the standard read() methods rather than relying on the buggy versions built into Java. Example 4-1 of Java Network Programming shows you how to do this. See Example 4-1 on Cafe au Lait

[Paul Santa Maria]

Mihir -

Please be sure to post back to the group and let us know if changing "readLine()" (which is very definitely susceptible to hangs under far too many scenarios) to "read()" (inside of a loop) fixed the problem.

Thanx in advance .. PSM

[Ko Ko Naing]

Guys,
mihir sent me his source codes for server and client as private. Here it is.

client code
 
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.net.*;
class MyJFrame extends JFrame implements ActionListener,WindowListener,Runnable
{
JFrame jf=null;
JButton login=null;
JButton clear=null;
JLabel username=null;
JLabel password=null;
JTextField jtf1=null;
JTextField jtf2=null;
JPanel jp1=null;
File f=null;
File sourcefile=new File("c:\sourcefile.txt");
FileReader fr=null;
BufferedReader bfr=null;
FileWriter fw=null;
BufferedWriter bfw=null;
String pathsourcefile=null;
Vector registeredusers=null;
JOptionPane jopt=null;
boolean recordfound=false;
String nextelement="";
String enteredtext="";
Socket s=null;
InputStream is=null;
InputStreamReader isr=null;
BufferedReader clientbfr=null;
OutputStream os=null;
OutputStreamWriter osw=null;
BufferedWriter clientbfw=null;
String rfreturn=null;
String temp=null;
boolean always=true;
MyJFrame()
{
jp1=new JPanel(new GridLayout(3,2));
username=new JLabel("Username");
password=new JLabel("Password");
jtf1=new JTextField(20);
jtf2=new JTextField(20);
login=new JButton("Login");
login.setSize(1,1);
clear=new JButton("Clear");
//jp1=new JPanel();
jp1.add(username);
jp1.add(jtf1);
jp1.add(password);
jp1.add(jtf2);
jp1.add(login);
jp1.add(clear);
getContentPane().add(jp1,BorderLayout.NORTH);
setSize(400,150);
setResizable(false);
setVisible(true);
login.addActionListener(this);
clear.addActionListener(this);
addWindowListener(this);
}
 
public void run()
{
try
{
System.out.println("Thread Started.");
String temp1="";
temp1=clientbfr.readLine();
System.out.println(temp1);
 
}
catch(Exception e)
{
System.out.println("Error in the thread="+e.getMessage());
}
System.out.println("Thread Ended.");
}
 
public String readSourceFile(String s,String s1)
{
try
{
fr=new FileReader(s);
bfr=new BufferedReader(fr);
String temp="";
while((temp=bfr.readLine()).indexOf(s1)!=0)
{
//System.out.println(temp);
}
rfreturn=temp.substring(s1.length());
return rfreturn;
}
catch(Exception e)
{
System.out.println("Error while reading source file."+e.getMessage());
return null;
}
}
 
public void readRegisteredFile(String s)
{
try
{
f=new File(s);
fr=new FileReader(f);
bfr=new BufferedReader(fr);
String temp="";
while((temp=bfr.readLine())!=null)
{
registeredusers.add(temp);
}
}
catch(Exception e)
{
System.out.println("Error while reading users file."+e.getMessage());
}
}
public void actionPerformed(ActionEvent ae)
{
 
if(ae.getActionCommand().trim().equalsIgnoreCase("login"))
{
String name=jtf1.getText();
String pass=jtf2.getText();
if((name.trim().equals(""))||(pass.trim().equals("")))
{
jopt=new JOptionPane("ChatServer");
jopt.showMessageDialog(jf,"Please enter the username or password","Error",JOptionPane.OK_OPTION);
}
else
{
// now put this entire code on the server side because server will do the validation.
//here read the path of the ip address and the port from the config file.
try
{
pathsourcefile=readSourceFile(sourcefile.toString(),"server-");
if(pathsourcefile==null)
{
jopt.showMessageDialog(jf,"You cannot proceed as the source file is corrupt.","Error",JOptionPane.OK_OPTION);
}
else
{
try
{
// now u r getting the address where you need to connect. so please connect.
enteredtext=jtf1.getText().trim()+"-"+jtf2.getText().trim();
if(s==null)
{
s=new Socket(pathsourcefile.substring(0,pathsourcefile.indexOf(",")),Integer.parseInt(pathsourcefile.substring(pathsourcefile.indexOf(",")+1)));
is=s.getInputStream();
isr=new InputStreamReader(is);
clientbfr=new BufferedReader(isr);
os=s.getOutputStream();
osw=new OutputStreamWriter(os);
clientbfw=new BufferedWriter(osw);
}
clientbfw.write("Login-"+enteredtext+"\n");
clientbfw.flush();
this.run();
}
catch(Exception e)
{
System.out.println("Error while connecting=");
e.printStackTrace();
}
}
}
catch(Exception e)
{
//jopt.showMessageDialog(jf,"Error while reading the configuration file ","Error",JOptionPane.OK_OPTION);
System.out.println("Error while connecting =");
e.printStackTrace();
}
}
}
if(ae.getActionCommand().trim().equalsIgnoreCase("clear"))
{
jtf1.setText("");
jtf2.setText("");
}
}
public void windowClosing(WindowEvent ae)
{
//System.out.println("wc "+ae);
System.exit(0);
}
public void windowOpened(WindowEvent ae)
{
//System.out.println("wOpened "+ae);
}
public void windowClosed(WindowEvent ae)
{
//System.out.println("wclosed "+ae);
}
public void windowIconified(WindowEvent ae)
{
//System.out.println("wIconified "+ae);
}
public void windowDeiconified(WindowEvent ae)
{
//System.out.println("wDeiconified "+ae);
}
public void windowActivated(WindowEvent ae)
{
//System.out.println("wActivated "+ae);
}
public void windowDeactivated(WindowEvent ae)
{
//System.out.println("wDeactivated "+ae);
}
public static void main(String[] args) 
{
//System.out.println("Hello World!");
MyJFrame mjf= new MyJFrame();
}
}
 
 
server code
 
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.net.*;
class MyServer implements Runnable
{
InputStream ips=null;
InputStreamReader ipsr=null;
BufferedReader bfr=null;
BufferedReader clientbfrresponse=null;
OutputStream ops=null;
OutputStreamWriter opsw=null;
BufferedWriter clientbfw=null;
FileReader fr=null;
ServerSocket ss=null;
Socket s=null;
boolean always=true;
String temp="";
String rfreturn=null;
String pathsourcefile=null;
JOptionPane jopt=null;
File sourcefile=null;
Vector registeredusers=null;
File f=null;
boolean recordfound=false;
String nextelement="";
MyServer()
{
try
{
sourcefile=new File("c:\sourcefile.txt");
ss=new ServerSocket(2000);
System.out.println("Waiting for a request.");
while(always)
{
s=ss.accept();
System.out.println("I have received a request.");
ips=s.getInputStream();
ipsr=new InputStreamReader(ips);
clientbfrresponse=new BufferedReader(ipsr);
ops=s.getOutputStream();
opsw=new OutputStreamWriter(ops);
clientbfw=new BufferedWriter(opsw);
this.run();
}
}
catch(Exception e)
{
System.out.println("Error while receiving request="+e.getMessage());
}
}
 
public void readRegisteredFile(String s)
{
try
{
f=new File(s);
fr=new FileReader(f);
bfr=new BufferedReader(fr);
String temp="";
while((temp=bfr.readLine())!=null)
{
registeredusers.add(temp);
}
}
catch(Exception e)
{
System.out.println("Error while reading users file."+e.getMessage());
}
}
 
 
public String readSourceFile(String s,String s1)
{
try
{
fr=new FileReader(s);
bfr=new BufferedReader(fr);
String temp="";
while((temp=bfr.readLine()).indexOf(s1)!=0)
{
//System.out.println(temp);
}
rfreturn=temp;//.substring(s1.length());
return rfreturn;
}
catch(Exception e)
{
System.out.println("Error while reading source file."+e.getMessage());
return null;
}
}
 
public void run()
{
System.out.println("Thread Started.");
try
{
while(true)
{
temp=clientbfrresponse.readLine();
if(temp==null)
{
//System.out.println("No data received.");
}
else if(temp.indexOf("Login-")==0)
{
//check if the student is logged in.
try
{
temp=temp.substring(6);
pathsourcefile=readSourceFile(sourcefile.toString(),"file-");
if(pathsourcefile==null)
{
jopt.showMessageDialog(null,"You cannot proceed as the source file is corrupt.","Error",JOptionPane.OK_OPTION);
}
else
{
registeredusers=new Vector();
pathsourcefile=pathsourcefile.substring(pathsourcefile.indexOf("file-")+5);
//System.out.println("--"+pathsourcefile);
readRegisteredFile(pathsourcefile);
//enteredtext=jtf1.getText().trim()+"-"+jtf2.getText().trim();
Enumeration e=registeredusers.elements();
while(e.hasMoreElements())
{
nextelement=(String)e.nextElement();
System.out.println(temp+"/"+nextelement);
if(temp.equals(nextelement))
{
recordfound=true;
}
}
String message="";
if(recordfound)
{
//System.out.println("yes");
clientbfw.write("Login-yes"+"\n");
clientbfw.flush();
}
else
{
//System.out.println("no");
clientbfw.write("Login-no"+"\n");
clientbfw.flush();
}
recordcount=false;
}
}
catch(Exception e)
{
System.out.println("Error while reading the files="+e.getMessage());
}
}
else if(temp.indexOf("Data")==0)
{
 
}
 
//System.out.println(temp);
}
}
catch(Exception e)
{
System.out.println("Error while receving data=");
e.printStackTrace();
}
System.out.println("Thread Ended.");
}
public static void main(String[] args) 
{
//System.out.println("Hello World!");
MyServer ms=new MyServer();
}
} 

Well, u guys might want to compile them and run them. He asked my help in the private message. I am going to find the errors out soon. If u guys see anything wrong with the codes, please don't hesititate to point them here... Thanks...
[ December 08, 2004: Message edited by: Ko Ko Naing ]

[alex balka]

I would like to comment the usage of readLine() in the while loop:
When using readLine() in a loop for reading from a file, readLine stopps when the file ends. The socket ends when it is closed, i.e.readLine() in a while loop for reading from a socket will wait forever until the socket is closed.

[David Harkness]

If you can use JDK 1.4+, you might want to check out the new I/O packages (java.nio.*). This ONJava article covers using non-blocking sockets.

Certainly there is a solution to your current issue using the standard I/O packages (I admit I haven't read this whole thread), but if this project is for learning, here's another area for exploration.