Socket connection validity

Hi,
I have connected my client to a server and did some operation and then left teh client for sometime. Now after sometime..I want to do some operation on teh same connection,but before that I want to check the validty of connection i.e whether the connection is still alive or not. Does Java has any API to check taht whether the connection is alive or not.
Or does someone knows how I send a keepalive packet from my application.

ok, this is my last attempt to tell you how it is....
you want to send some sort of test packet, if its ok, you continue to send your data. so heres what happens
pass...
client: send TCP test
server: ok
client: send data
fail...
client: send TCP test
server: nothing because the connection has failed
client: generates IOException because you tried to use a Socket thats no longer conected
client: create new connection
client: send data
why ever not
pass...
client: send data
fail...
client: send data
server: nothing because the connection has failed
client: generates IOException
client: create new connection
client: send data

Similar Messages

Urgent --- Persistent socket connection?

Hi, I have a question about the persistency of a Java Socket connection. Is it a valid idea to keep a java socket open for a long time? If so, what special care do I need to take?
My Java TCP/IP client runs as a NT service. It keeps getting input messages every few seconds, then send it thru a socket connection to a TCP/IP server. In order to avoid the overhead of opening and closing the socket every time the client gets a message to send, I want to keep the socket connection open and reuse it.
I was able to send hundreds of messages thru this way, then after a while, for no apparent reason,
the socket stops working, I typically get an exception like this:
java.net.SocketException: Connection Shutdown: JVM_recv in socket input stream read
at java.net.SocketInputStream.socketRead(Native Method)
at java.net.SocketInputStream.read (SocketInputStream.java:90)
at java.net.SocketInputStream.read (SocketInputStream.java:71)
at java.io.InputStreamReader.fill (InputStreamReader.java:163)
at java.io.InputStreamReader.read (InputStreamReader.java:239)
at java.io.BufferedReader.fill (BufferedReader.java:137)
at java.io.BufferedReader.readLine (BufferedReader.java, Compiled Code)
at java.io.BufferedReader.readLine (BufferedReader.java:329)
My programs runs on NT4.0, single-threaded. Any input would be greatly appreciated.

Is it a valid idea to keep a java socket open for a long time? If so, what
special care do I need to take?Depends.
First why keep it open? Your messages only arrive every couple of seconds, does opening/closing the connection take longer than that?
If you must then the complication you must deal with is that your code must deal with re-establishing the connection when it does fail. Opening/closing it every time avoids that issue. The connection will fail, because computers fail, networks fail and people make mistakes. Which doesn't mean that you shouldn't but merely that you should consider the implications of why you need to keep it open.

Sockets connection

Can anybody help me how to connect Flash to a server Using Sockets connection using in AS3.

Use following code UPDATED:
try
var mySocket:Socket = new Socket();
var isConnected:Boolean = false;
var portNumber:Number =8000; //Enter Port number you want to use instead of 8000;
var IPAddress:String = "localhost"; //Enter server IP instead of localhost;
//Valid range of port numbers is 1 to 65535
if (portNumber >= 1 && portNumber <= 65535)
//Create new socket.
mySocket=new Socket ;
//Connect to host and port.
mySocket.connect(IPAddress,portNumber);
//Add listeners to socket to start communicating with the server.
mySocket.addEventListener(IOErrorEvent.IO_ERROR,errorOccured);
mySocket.addEventListener(SecurityErrorEvent.SECURITY_ERROR,errorOccured);
mySocket.addEventListener(ProgressEvent.SOCKET_DATA,readFromServer);
mySocket.addEventListener(Event.CONNECT,connectionEstablished);
else
//Show error message
trace("Server is not reachable on port " + portNumber + ".");
ExternalInterface.call("alert","Server is not reachable on port " + portNumber + ".");
catch (e)
//Show error message
trace("Server is not reachable.");
ExternalInterface.call("alert","Server is not reachable.");
function readFromServer(evnt:ProgressEvent):void
//Read message
var str:String = mySocket.readUTFBytes(mySocket.bytesAvailable);
//Remove line breaks.
while (str.indexOf("\n") > -1)
str = str.replace("\n","");
while (str.indexOf("\r") > -1)
str = str.replace("\r","");
//Message from server received...
trace(str);
function writeToServer(toUserName:String, messageStr:String):void
if (isConnected)
var pushStr = "Message from Flash to server";
mySocket.writeUTFBytes(pushStr);
mySocket.flush();
//This function is called when connection to server is successful.
function connectionEstablished(evnt:Event)
//Mark socket connection with the server as connected.
isConnected = true;
function errorOccured(evnt:Event)
//Some error occured
trace("Some error occured!");
ExternalInterface.call("alert","Some error occured!");

Socket.connect

I'm trying to write a client application that will connect to a server whenever it becomes available. There are some problems which I hope someone will be able to help, Below is a snippet of the code that makes the connection:
while(alive){
try{
/* part 1*/
Socket s = new Socket();
s.setReuseAddress(true);
s.bind(localAddress);
/* end part 1*/
s.connect(targetAddress);
} catch (Exception e){}
this seems to works fine. However when I place part 1 of the code outside the while loop. the connection will not be made if the server application is up after my connection thread has started running. Isnt Socket.connect suppose to block until a valid connection is made?
Also when running my application (with the code above) over a long period of time, I get a OutOfMemoryException (native memory) when the server application is not present. Do I have to specify some other parameters for the JVM to release the native resources allocated for a socket construction or is this just a bug? I am running the application using java 1.6 on RHEL4 2.6.9-34.ELSMP.
Thank you in advance.

The thread is respawned when then server application
drops thus yes the socket will only make one
connection.Not if you move part 1 out of the loop.If you do that you will attempt multiple connections with the socket, which doesn't work.
Shouldnt the thread block when .connect() fails?Why? Block doing what?
Instead i'm getting a connection refused exception.What else should it do?
No i did not close the socket when I get an exception.You should.
Should the resources be reclaimed since
the socket object would have gone out of scope?Eventually.
I'm running my application on a system with multiple
network cards thus i need to bind it to the intended
address.Why? TCP/IP will find the best route if you don't get in its way. Why not let it?

Java Socket Connection Time out

Goal*
I want to check host/port availability of computers in our network (~100 computers) .. Just check if host is alive and if it has port 445 opened. I want to do this somehow in parallel, so the code execution is as quick as possible.
My implementation*
I do this by creating socket connection to the host. Something like this:
        Socket s = null;
        try {
            s = new Socket();
            InetSocketAddress socketAddress = new InetSocketAddress(ipAddress, 445);
            s.connect(socketAddress, 3000);
            if (s.isConnected()) {
                // do something
        } catch (ConnectException ex) {
            //exception thrown
        } catch (IOException ex1) {
            //exception thrown
        } finally {
            try {
                // close socket
                s.close();
            } catch (IOException ex) {
                Logger.getLogger(ComputerModel.class.getName()).log(Level.SEVERE, null, ex);
        }This code is executed in a loop, where a separate thread is created for every iteration = ~100 separate threads.
Problem:*
1.
It seems to me, that first ~10-15 connections are created ok, but then my code reaches 'IOException' catch block for every subsequent itteration and ex.getMessage() returns "connection time out" (I try to use different timeout values in the 2nd parameter. Values from 3000 up to 20000).
Is it valid to create 100 separate threads in a loop? Can't I make my NIC to bussy with this ??? What is the maximum ammount of threads, I can create? I did not use threads before, so I have no idea, if max values are near to 10, 100, 1000, or 10000 ..
2.
After my code is executed, I enter 'netstat -an' command in my command line and I get bunch of connections, which report status of SYN_SENT for several connections.
TCP 10.20.11.140:4557 10.30.11.119:445 SYN_SENT
TCP 10.20.11.140:4558 10.30.11.176:445 SYN_SENT
TCP 10.20.11.140:4559 10.30.11.100:445 SYN_SENT
TCP 10.20.11.140:4560 10.30.11.142:445 SYN_SENT
TCP 10.20.11.140:4561 10.30.11.171:445 SYN_SENT
TCP 10.20.11.140:4562 10.30.11.143:445 SYN_SENT
TCP 10.20.11.140:4563 10.30.12.12:445 SYN_SENT
TCP 10.20.11.140:4564 10.30.12.11:445 SYN_SENT
TCP 10.20.11.140:4565 10.30.12.21:445 SYN_SENT
TCP 10.20.11.140:4566 10.30.11.150:445 SYN_SENT
I also feel, that my computer network response (e.g. firefox browsing) is a bit slower ..
How shall I handle this problem properly?
Thx in advance,
Juraj

kajbj wrote:
tschodt wrote:
kajbj wrote:
The documentation for netstat explains what SYN_SENT is, but
I don't know why you have them.The app has asked the TCP stack to transmit SYN
the TCP stack is now waiting for SYN-ACK.
If there is no host at that IP address or a host that drops connections (SYN packets) for TCP port 445
there will never be a SYN-ACK.
After a few minutes the TCP stack will time out the connection attempt.Yes, I was rather commenting on why his hosts aren't answering. I thought that his case was that all of them should answer :)Akkurat. I was answering more for clarification.
Someone who does not know your posting history could easily assume you meant
it was a mystery why netstat was showing SYN_SENT.
And I figured it would not harm to hint that one possible reason would be that those machines are powered off (no host).

Socket connect slow in JDK 1.5?

We recently began testing our Java Swing application with JDK 1.5, and we noticed that socket.connect()
calls are taking several seconds to return, when before in 1.4 the calls returned immediately.
Here is some sample code:
Socket sock = new Socket();
InetSocketAddress sockAddr = new InetSocketAddress(inAddress, portNum);
sock.connect(sockAddr, 2000);
What could be wrong? I've debugged the code and verified inAddress is an IP address,
not a hostname.
-Eric

Here is the list of enhancements in JDK1.5.
http://java.sun.com/j2se/1.5.0/docs/guide/net/enhancements-1.5.0.html
I wonder if any of them are having some effect in the slow connection.
There are some network properties that you can tweak with. Did you try them?
Here is the list
http://java.sun.com/j2se/1.5.0/docs/guide/net/properties.html

Is there any way to identify the particular socket connection is closed ?

Is there any way to identify the particular socket connection is closed or not ?
Any methods ???
How can the program knows the connection is lost or some thing ...
Is the socket throws some excpetions when there is no active connection ???
namanc

If you get an IOException when you try to use the socket, the connection was obviously closed.
The correct way for an application to know if the socket was closed is:
1) the server sends a message indicating that the socket should be closed
2) the client closes the socket itself

I suppose it is the problem with socket connection,Please help

Hi,
I'm trying to build a chat server in Java on Linux OS.I've created basically 2 classes in the client program.The first one shows the login window.When we enter the Login ID & password & click on the ok button,the data is sent to the server for verification.If the login is true,the second class is invoked,which displays the messenger window.This class again access the server
for collecting the IDs of the online persons.But this statement which reads from the server causes an exception in the program.If we invoke the second class independently(ie not from 1st class) then there is no problem & the required data is read from the server.Can anyone please help me in getting this program right.I'm working on a p4 machine with JDK1.4.
The Exceptions caused are given below
java.net.SocketException: Connection reset by peer: Connection reset by peer
at java.net.SocketInputStream.SocketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:119)
     at java.io.InputStreamReader$CharsetFiller.readBytes(InputStreanReader.java :339)
     at java.io.InputStreamReader$CharsetFiller.fill(InputStreamReader.java:374)
     at java.io.InputStreamReader.read(InputStreamReader.java:511)
     at java.io.BufferedReader.fill(BufferedReader.java:139)
     at java.io.BufferedReader.readLine(BufferedReader.java:299)
     at java.io.BufferedReader.readLine(BufferedReader.java:362)
     at Login.LoginData(Login.java:330)
     at Login.test(Login.java:155)
     at Login$Buttonhandler.actionPerformed(Login.java:138)
     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1722)
     at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:17775)
     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:4141)
     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:253)
     at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:261)
     at java.awt.Component.processMouseEvent(Component.java:4906)
     at java.awt.Component.processEvent(component.java:4732)
     at java.awt.Container.processEvent(Container.java:1337)
     at java.awt.component.dispatchEventImpl(Component.java:3476)
     at java.awt.Container.dispatchEventImpl(Container.java:1399)
     at java.awt.Component.dispatchEvent(Component.java:3343)
     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:3302)
     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3014)
     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:2967)
     at java.awt.Container.dispatchEventImpl(Container.java:1373)
     at java.awt.window.dispatchEventImpl(Window.java:1459)
     at java.awt.Component.dispatchEvent(Component.java:3343)
     at java.awt.EventQueue.dispatchEvent(EventQueue.java:439)
     at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:150)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:136)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:131)
     at java.awt.EventDispatchThread.run(EventDispatchThread.java:99)
     My program looks somewhat like this :
1st class definition:
public class Login extends Jframe// Login is the name of the first class;
Socket connection;
DataOutputStream outStream;
BufferedReader inStream;
Frame is set up here
public class Buttonhandler implements ActionListener
public void actionPerformed(ActionEvent e) {
String comm = e.getActionCommand();
if(comm.equals("ok")) {
check=LoginCheck(ID,paswd);
test();
public void test() //checks whether the login is true
if(check)
new Messenger(ID);// the second class is invoked
public boolean LoginCheck(String user,String passwd)
//Enter the Server's IP & port below
String destination="localhost";
int port=1234;
try
connection=new Socket(destination,port);
}catch (UnknownHostException ex){
error("Unknown host");
catch (IOException ex){
ex.printStackTrace ();
error("IO error creating socket ");
try{
inStream = new BufferedReader(new InputStreamReader(connection.getInputStream()));
outStream=new DataOutputStream(connection.getOutputStream());
}catch (IOException ex){
error("IO error getting streams");
ex.printStackTrace();
System.out.println("connected to "+destination+" at port "+port+".");
BufferedReader keyboardInput=new BufferedReader(new InputStreamReader(System.in));
String receive=new String();
try{
receive=inStream.readLine();
}catch(IOException ex){ error("Error reading from server");}
if(receive.equals("Logintrue"))
check=true;
else
check=false;
try{
inStream.close();
outStream.close();
connection.close();
}catch (IOException ex){
error("IO error closing socket");
return(check);
// second class is defined below
public class Messenger
Socket connect;
DataOutputStream outStr;
BufferedReader inStr;
public static void main(String args[])
{ Messenger mes = new Messenger(args[0]);}
Messenger(String strg)
CreateWindow();
setupEvents();
LoginData(strg);
fram.show();
void setupEvents()
fram.addWindowListener(new WindowHandler());
login.addActionListener(new MenuItemHandler());
quit.addActionListener(new MenuItemHandler());
button.addActionListener(new Buttonhandle());
public void LoginData(String name)
//Enter the Server's IP & port below
String dest="localhost";
int port=1234;
int r=0;
String str[]=new String[40];
try
connect=new Socket(dest,port);
}catch (UnknownHostException ex){
error("Unknown host");
catch (IOException ex){
ex.printStackTrace ();
error("IO error creating socket ");
try{
inStr = new BufferedReader(new InputStreamReader(connect.getInputStream()));
outStr=new DataOutputStream(connect.getOutputStream());
}catch (IOException ex){
error("IO error getting streams");
ex.printStackTrace();
String codeln=new String("\n");
try{
outStr.flush();
outStr.writeBytes("!@*&!@#$%^");//code for sending logged in users
outStr.writeBytes(codeln);
outStr.write(13);
outStr.flush();
String check="qkpltx";
String receive=new String();
try{
while((receive=inStr.readLine())!=null) //the statement that causes the exception
if(receive.equals(check))
break;
else
     str[r]=receive;
     r++;
}catch(IOException ex){ex.printStackTrace();error("Error reading from socket");}
catch(NullPointerException ex){ex.printStackTrace();}
} catch (IOException ex){ex.printStackTrace();
error("Error reading from keyboard or socket ");
try{
inStr.close();
outStr.close();
connect.close();
}catch (IOException ex){
error("IO error closing socket");
for(int l=0,k=1;l<r;l=l+2,k++)
if(!(str[l].equals(name)))
stud[k]=" "+str[l];
else
k--;
public class Buttonhandle implements ActionListener
public void actionPerformed(ActionEvent e) {
//chat with the selected user;
public class MenuItemHandler implements ActionListener
public void actionPerformed(ActionEvent e)
String cmd=e.getActionCommand();
if(cmd.equals("Disconnect"))
//Disconnect from the server
else if(cmd.equals("Change User"))
     //Disconnect from the server & call the login window
else if(cmd.equals("View Connection Details"))
//show connection details;
public class WindowHandler extends WindowAdapter
public void windowClosing(WindowEvent e){
//Disconnect from server & then exit;
System.exit(0);}
I�ll be very thankful if anyone corrects the mistake for me.Please help.

You're connecting to the server twice. After you've successfully logged in, pass the Socket to the Messenger class.
public class Messenger {
    Socket connect;
    public static void main(String args[]) {
        Messenger mes = new Messenger(args[0]);
    Messenger(Socket s, String strg) {
        this.connect = s;
        CreateWindow();
        setupEvents();
        LoginData(strg);
        fram.show();
}

Problem with socket connection

have my gps reciver connected to the usb port - i have a daemon gpsd running which makes data available on tcp port 2947 for querying. when i do telnet, it gives proper data.
but when i open a socket connection using java, it does not print anything as output. actually telnet asks for an escape charatcer so i am sending "r" initially to the server but still the program does not print anything as output.
here is my java code -
import java.io.*;
import java.net.Socket;
public class test2
public static void main(String[] args)
try
Socket s = new Socket("localhost",2947);
PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
s.getOutputStream())),true);
out.println("r");
BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
String line;
while(true)
line = in.readLine();
System.out.println(line);
catch (Exception e)
or sometimes it even shows error as
Exception in thread "main" java.net.SocketException: Invalid argument or cannot assign requested address
at java.net.PlainSocketImpl.socketConnect(Native Method)
and this is the output which i get on telnet -
ot@localhost ~]# telnet localhost 2947
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
r
GPSD,R=1
$GPRMC,000212,V,18000.0000,N,00000.0000,W,0.0000,180.000,101102,,*1A
$GPGSA,A,1,,,,,,,,,,,,,,,,*32
$PGRME,400.00,0.00,0.00*7B
$GPRMC,000213,V,18000.0000,N,00000.0000,W,0.0000,180.000,101102,,*1B
$GPGSA,A,1,,,,,,,,,,,,,,,,*32
$PGRME,400.00,0.00,0.00*7B
$GPRMC,000214,V,18000.0000,N,00000.0000,W,0.0000,180.000,101102,,*1C
$GPGSA,A,1,,,,,,,,,,,,,,,,*32

Actually the problem does not seem to be in the code because i tried some basic client server programs (without any gpsd etc in picture) and even they are not working in linux though they work perfectly in windows (on the same machine). In linux it shows exception
My socket programs dont work in linux it shows error -
ot@localhost winc]# java parser
Exception in thread "main" java.net.SocketException: Invalid argument or cannot assign requested address
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:305)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:171)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:158)
at java.net.Socket.connect(Socket.java:452)
at java.net.Socket.connect(Socket.java:402)
at java.net.Socket.<init>(Socket.java:309)
at java.net.Socket.<init>(Socket.java:124)
at parser.main(parser.java:10)
i have removed the firewall settings etc and it still doesnot work in linux
what could be the cause for this?
Sowmya

Problem with socket connection through Java Embedding...

We are trying to create a simple socket connection to a socket server through BPEL PM using the Java Embedding component.
BPEL Process : Client makes an asynchronous request. Passes an input variable. The input variable is sent to the Server Program through a socket connection through the Java embedding component.
Server: We are running a simple Socket Server program from command prompt.
The code below works fine as long as we do not try to receive a response from the server (Commented Code).
If we uncomment the code and try to receive a response, it refuses to create an instance for the BPEL Process. And sometimes restarts the BPEL Server.
Client Code:
String msg="NONE";
try{
org.w3c.dom.Element input = (org.w3c.dom.Element) getVariableData("inputVariable","payload","/client:clientProcessRequest/client:input");
msg = input.getNodeValue();
Socket clientsoc=new Socket("ServerIP",1000);
PrintWriter out1=new PrintWriter(clientsoc.getOutputStream());
out1.write(msg);
out1.flush();
BufferedReader cin1=new BufferedReader(new InputStreamReader(clientsoc.getInputStream()));
msg=cin1.readLine();
setVariableData("outputVariable","payload","/client:result",new String(msg));
clientsoc.close();
catch(UnknownHostException e)
System.err.println("Don't know about host: dev.");
System.exit(1);
catch (IOException e)
System.err.println("Couldn't get I/O for "+ "the connection to: dev.");
System.exit(1);
}

Repost

Problem with socket connection in midp 2.0

hello everyone.
I'm new one in j2me and I am learning socket connection in j2me. I'm using basic socket,datagram example wich is come with sun java wireless toolkit 2.5. for it i wrote small socket server program on c# and tested it example on my pc and its working fine. also socket server from another computer via internet working fine. But when i instal this socket example into my phone on nokia n78 (Also on nokia 5800) it's not working didn't connect to socket server.. On phone I'm using wi-fi internet. Can anybody help me with this problem? I hear it's need to modify manifest file and set appreciate pressions like this
MIDlet-Permissions: javax.microedition.io.Connector.socket,javax.microedition.io.Connector.file.write,javax.microedition.io.Connector.ssl,javax.microedition.io.Connector.file.read,javax.microedition.io.Connector.http,javax.microedition.io.Connector.https
is it true?
can anybody suggest me how can i solve this problem?
where can I read full information about socket connection specifiecs in j2me?
Thanks.

Maybe this can be helpful:
[http://download-llnw.oracle.com/javame/config/cldc/ref-impl/midp2.0/jsr118/index.html]
you can check there the Datagram interface anda DatagramConnection interface and learn a little about that.
If the client example runs fine in the wireless toolkit emulator, it should run the same way in your phone; i suggest to try to catch some exception that maybe is hapenning and display it on a Alert screen, this in the phone.

How to make a socket connection timeout infinity in Servlet doPost method.

I want to redirect my System.out to a file on a remote server (running Apache Web Server and Apache Tomcat). For which I have created a file upload servlet.
The connection is established only once with the servlet and the System.out is redirected to it. Everything goes fine if i keep sending data every 10 second.
But it is required that the data can be sent to the servlet even after 1 or 2 days. The connection should remain open. I am getting java.net.SocketTimeoutException: Read timed out Exception as the socket timeout occurs.
Can anyone guide me how to change the default timeout of the socket connection in my servlet class.
Following is the coding to establish a connection with the Servlet.
URL servletURL = new URL(mURL.getProtocol(), mURL.getHost(), port, getFileUploadServletName() );
URLConnection mCon = servletURL.openConnection();
mCon.setDoInput(true);
mCon.setDoOutput(true);
mCon.setUseCaches(false);
mCon.setRequestProperty("Content-Type", "multipart/form-data");
In the Servlet Code I am just trying to read the input from the in that is the input stream.
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
BufferedInputStream in = new BufferedInputStream(req.getInputStream());
byte [] content = new byte[1024];
do
read = in.read(content, 0, content.length);
if (read > 0)
out.write(content, 0, read);
I have redirected the System.out to the required position.
System.setOut(........);
Can anyone guide me how to change the default timeout of the socket connection in my servlet class.

I am aware of the setKeepAlive() method, but this can only used with the sockets. Here i am inside a servlet, have access to HTTPServletRequest and HTTPServletResponse and I don't know how to get access to the underlying sockets as the socket handling will be handled by the tomcat itself. If I am right there will be method in the apache tomcat 6.0.x to set this property. But till now I am not getting it.

Multiple clients on socket connection

Hi!
I understand that it is possible that multiple clients listen to one server (on the same port) and even write to it (then it should be a multi-threaded server).
But i would like to refuse connectios, if one client is connected. How can I do that?
In my case I have a (single threaded) server. Now one clients connects. The server waits to receive data from the client and answers, without ever closing the port. that works.
Now if I connect with a second client, the openicng of the socket in the second client works fine, although the server does not seem to notice the second client. Communication is not possible between the server and the second client, and the server doesn't answer to the first client anymore, although he receives data from it.
So, since the server does not seem to notice the second client (does not accept the connection) and I don't get an exception at the second client, what can I do?
Thank you for your help!
concerned Code (if you want to take a look at it):
CLIENT:
socket = new Socket(hostname, echo_port);
SERVER:
try
ServerSocket waitingsocket = new ServerSocket(echo_port);
try
     socket= waitingsocket.accept();
     System.out.println("Client connected");
     ReaderThread reader = new ReaderThread( this, socket );
     reader.start();
catch (Exception e)
READER:
public void run()
     while (true)
          try {
               int bytesRead = inStream.read(inputBuffer,
               0, inputBuffer.length);
               readCallback.tcpUpdate(inputBuffer,bytesRead);
          catch (Exception oops)
               readCallback.tcpUpdate(null,-1);


Just to make sure this is clear: You can NOT have multiple clients on a given socket connection. You CAN have multiple clients connected to a particular port on a given server, but each client will be communicating with the server through a different of socket.
The usual approach here is to set up a listening ServerSocket on the desired port, call accept() on it, then process the communication from the returned Socket object. This is usually done by spawning a new thread and allowing it to handle the socket communication, while the ServerSocket loops around to another accept() for the next communication.
Here's an excellent intro to the concepts (the code is really ugly and poorly implemented, but it does a good job of explaining the overall concept). I used this as a starting point, and now (after a whole lot of development) have a pretty sweet extensible web server class that handles template expansion, etc... (I use this as a quick and dirty UI for some of my apps, instead of requiring the user to install a JSP container):
http://developer.java.sun.com/developer/technicalArticles/Networking/Webserver/
- K

How can i reuse my existing socket connection

Hi,
this might sound basic, it probably is:
As part of my larger project, i have to send and recieve data to multiple socket connections.
The thing that happens is that everytime i send data, it seems that java is creating a new stream or something (code is multithreaded)
so as i send 4 items of data, a bit like a chat program sending 4 statements, it creates 4 different streams, instead of using the same stream. therefore when i close the connection, i get:
java.net.SocketException: Connection reset 4 times.
i know why.. its because i have added the:
Socket socket=new Socket(host, port);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
bit in the same method with the
out.println(THE DATA....);
out.flush();
The thing what i want to do is to create the connection one, and reuse the objects:
out, in and socket
to send / recieve the new data.
please help me guys,
thanks

All the threads would be able to get the same reference to....
class SocketWrapper {
     private final Object readLock = new Object();
     private final Object writeLock = new Object();
     // client side
    public SocketWrapper(String hostname, int port);
     // server side.
    public SocketWrapper(Socket);
     // send data
     public void send(Serializable object) throws IOException;
     // receive data. synchronized(writeLock);
     public Serializable getNext() throws IOException;
     // create a new socket as required, throw IllegalState if server side. synchronized(readLock)
     private void createNewSocket() throws IllegalStateException;
}The send autoconnects as required. It then send on message/packet/object.
The getNext autoconnects as required. It reads one message/packet/object and returns.
This allows multiple threads to access the same socket. It allows data to be sent while a thread is blocking on a read. (Thus two locks)

How can i create a socket connection through an http proxy

i'm trying to make a socket connection send an email - i have code that works when you don't have to go through a proxy server but i can't make it pass the proxy server.
import java.net.*;
import java.io.*;
import java.util.*;
public class Mail
public String to_address = "[email protected]";
public String from_address = "[email protected]";
public String sendSub = "HeHeHe";
public String sendBody = "hehehe - it worked";
// This is created to allow data to be read in by the keyboard.
BufferedReader in = new BufferedReader(
new InputStreamReader(System.in));
     private void Mail(String to_address, // recipient's addresses
String from_address, // sender's address
String sendSub, // subject
String sendBody) // Message
               throws IOException, ProtocolException,      UnknownHostException {
     Socket socket;                // creates a Socket named socket
     PrintStream out;               // stream to write to socket
     String host = "imap.btopenworld.com";          // identification of the mail server host
// creates a new socket for connection to the mail server
// as well as two variables for the read and write streams
     socket = new Socket(host, 25); // opens socket to host on port 25 (SMTP port)
     out = new PrintStream(socket.getOutputStream());
// read the initial message
     in.readLine();
// Dialog with the mail server
// send HELO to SMTP server HELO command is given by a connecting SMTP host
     out.println( "HELO " + host );
     out.flush() ;
     in.readLine();
// Once we are connected to the mail server we start sending the email...
// send "from"
     out.println( "MAIL FROM: " + from_address );
     out.flush() ;
     in.readLine();
// send "to"
     out.println( "RCPT TO: " + to_address );
     out.flush() ;
     in.readLine();
// prepare the mailserver to receive the data
     out.println( "DATA" );
     out.flush() ;
     in.readLine();
// Send actual email
     out.println("From: " + from_address);
     out.println("To: " + to_address);
     out.println( "Subject: " + sendSub + "\n" );
     out.flush() ;
     out.println("");
     out.println( sendBody ) ;
     out.println(".") ; // standard to determine end-of-body
     out.flush() ;
     in.readLine();
//Quit and closes socket
     out.println("QUIT");
     out.flush();
     in.close() ;
     socket.close() ;
     return ;
public static void main (String [] args) throws IOException
Mail themail = new Mail();
}

i've tried that but it doesn't seem to do nething - this is how i implemented it...
import java.net.*;
import java.io.*;
import java.util.*;
public class Mail
public String to_address = "[email protected]";
public String from_address = "[email protected]";
public String sendSub = "HeHeHe";
public String sendBody = "hehehe - it worked";
// This is created to allow data to be read in by the keyboard.
BufferedReader in = new BufferedReader(
new InputStreamReader(System.in));
     private void Mail(String to_address, // recipient's addresses
String from_address, // sender's address
String sendSub, // subject
String sendBody) // Message
               throws IOException, ProtocolException,      UnknownHostException {
     Socket socket;                // creates a Socket named socket
     PrintStream out;               // stream to write to socket
     String host = "imap.btopenworld.com";          // identification of the mail server host
// creates a new socket for connection to the mail server
// as well as two variables for the read and write streams
     socket = new Socket(host, 25); // opens socket to host on port 25 (SMTP port)
     out = new PrintStream(socket.getOutputStream());
// read the initial message
     in.readLine();
System.getProperties().put( "proxySet", "true" );
          System.getProperties().put( "proxyHost", "144.124.16.28" );
          System.getProperties().put( "proxyPort", "8080" );
// Dialog with the mail server
// send HELO to SMTP server HELO command is given by a connecting SMTP host
     out.println( "HELO " + host );
     out.flush() ;
     in.readLine();
// Once we are connected to the mail server we start sending the email...
// send "from"
     out.println( "MAIL FROM: " + from_address );
     out.flush() ;
     in.readLine();
// send "to"
     out.println( "RCPT TO: " + to_address );
     out.flush() ;
     in.readLine();
// prepare the mailserver to receive the data
     out.println( "DATA" );
     out.flush() ;
     in.readLine();
// Send actual email
     out.println("From: " + from_address);
     out.println("To: " + to_address);
     out.println( "Subject: " + sendSub + "\n" );
     out.flush() ;
     out.println("");
     out.println( sendBody ) ;
     out.println(".") ; // standard to determine end-of-body
     out.flush() ;
     in.readLine();
//Quit and closes socket
     out.println("QUIT");
     out.flush();
     in.close() ;
     socket.close() ;
     return ;
public static void main (String [] args) throws IOException
Mail themail = new Mail();
}

Socket connection validity

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