I am setting up a simple TCP Client Server interaction in java.
Server:
The server is a desktop client written in Java:
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;
class TCPServer
{
public static int PORT_NUMBER = 6129;
public static void main(String argv[]) throws Exception
{
String clientMessage;
ServerSocket welcomeSocket = new ServerSocket(PORT_NUMBER);
while (true)
{
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
clientMessage = inFromClient.readLine();
System.out.println("Received: " + clientMessage);
outToClient.writeBytes("I received this: "+ clientMessage +"\n");
}
}
}
Client:
The client is an android app that connects to the server with TCP. In the client I have a method sendMessage(String msg) which attempts to send a message to the server.
public static void sendMessage(String msg) throws IOException
{
if (mainSocket == null)
{
return;
}
if (!mainSocket.isConnected())
{
connectSocket();
}
PrintWriter output = new PrintWriter( mainSocket.getOutputStream());
output.println(msg);
output.flush();
System.out.println(msg);
}
The problem is, the server receives the first message, but any subsequent messages won't show up at all. When I close the client down, all of a sudden all the other messages show up at once in the server.
This is what the server sees:
Received: message 1
No activity for a long time...
Then I shut down the client
Received: message 2 message 3 message 4 message 5 etc..
I put a println in the sendMessage() method, and the method itself is being called in real time.
You need to explicitly close() your PrintWriter on the client side each time you send a message. Same on the server side when you are done reading inFromClient, and again when you are done writing to outToClient.
See also this basic example, they explain the basic workflow quite nicely:
However, the basics are much the same as they are in this program:
Open a socket.
Open an input stream and output stream to the socket.
Read from and write to the stream according to the server's protocol.
Close the streams.
Close the socket.
Related
I have created a very very basic java server with tutorials. The goal is to let gamemaker studio 2 clients connect and communicate with that server. I have more experience with GML.
So the server is starting(java) up and the client(GMS2) is connecting succesfully. I have buildin some checks to make sure. If the client send a message to the server, the server never gets it, until the clients disconnect.
this is the java code:
import java.net.*;
import java.io.*;
public class GameServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = new ServerSocket(6666);
Socket client = serverSocket.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream(), true);
out.println("hello gamemaker studio: "); //the clients receive this message
while(true) {
System.out.println("in while loop");//the server console prints this message
String string = in.readLine();//keeps stuck on this
//after client disconnect, all messages the client has sent are displayed in the console
System.out.println("reading string:" + string);
if (string == null) { break; }
out.println("we have received this answer: " + string );
System.out.println("stopped");
}
}
}
For some reason i don't know it is keeps stuck on this line:
String string = in.readLine();
I crafted a java client to test it. Everything works fine with a java client.
So there has to be something wrong with the gamemaker code
I am new to java sockets, I am trying to create a simple UDP transmission using client-server. My problem now is the server is running the infinite loop and not sending message over to the client. Sorry if i did some stupid mistake, thanks
Server:
import java.net.*;
import java.util.*;
class EchoServer {
public static void main( String args[] ) throws Exception {
DatagramSocket socket = new DatagramSocket(54373);
DatagramPacket packet = new DatagramPacket(new byte[512],512);
String temp = "Hello client";
byte[] buffer = temp.getBytes();
while (true) {
socket.receive( packet );
System.out.println("Received from client");
DatagramPacket packet2 = new DatagramPacket(buffer,buffer.length,InetAddress.getByName("127.0.0.1"),54373);
socket.send( packet2 );
}
}
}
Client:
import java.net.*;
import java.util.*;
class EchoClient {
public static void main( String args[] ) throws Exception {
DatagramSocket socket = new DatagramSocket();
socket.setSoTimeout( 5000 );
byte[] buffer = "Hello Server".getBytes();
DatagramPacket packet = new DatagramPacket(buffer,buffer.length,InetAddress.getByName("127.0.0.1"),54373);
socket.send( packet );
DatagramPacket packet2 = new DatagramPacket(new byte[512],512);
socket.receive(packet2);
System.out.println("Received from server");
}
}
However, my server is able to send the original "packet" instead of packet2
Your server is sending back to itself. Instead of using its own port number when constructing the reply datagram, it should use the one that's already in the request datagram. And the IP address. In fact it should just send the request datagram as-is, as it's an echo server: no need to construct another one.
If the protocol changes the idea is to use the setData() method on the request to put the reply into it, again rather than creating a new datagram.
I'm trying to use SSL with IMAP in java. I do not want to use the IMAP class.
For some reason, when I send the n th message, I receive the answer to message n-2, and not to message n-1. Which means that I don't receive any answer to the first message sent until I send the second message. Can anyone spot what's wrong in the following minimal code ? (It is indeed minimal, apart from the println, which, I guess, help debugging)
import java.io.*;
import javax.net.ssl.*;
public class Mail{
static String server = "imap.gmail.com";
static String user = "straightouttascript#gmail.com";
static String pass = "azerty75";
public static void print (PrintWriter to, String text){
System.out.println("sent : "+text);
to.println(text+ "\r");
to.flush();
}
public static void read (BufferedReader from) throws InterruptedException, IOException {
do {
String line = from.readLine();
System.out.println("received: "+line);
} while (from.ready());
}
public static void main(String[] args){
try{
SSLSocket sslsocket = (SSLSocket) SSLSocketFactory.getDefault().createSocket(server, 993);
System.out.println("Start connexion");
BufferedReader from = new BufferedReader(new InputStreamReader(sslsocket.getInputStream()));
// read(from);
PrintWriter to = new PrintWriter(new BufferedWriter(new OutputStreamWriter(sslsocket.getOutputStream())), true);
print(to,"a1 login "+user+" "+pass);
read(from);/*exepcted:
OK gimap ready
a1 OK login#host authenticated (Success)*/
sslsocket.close();
System.out.println("End connexion");
}
catch (Exception e){
e.printStackTrace();
}
}
}
IMAP is not a pingpong protocol. The server doesn't send one line in response to one of yours.
Rather, you send commands and the server sends information. The server is permitted to send you more information than you asked for, so you can get seven responses to one command, and you can even get a response without sending a command at all, which is then called an unsolicited response. Strange phrase. Unsolicited responses are used by some servers to notify you about new mail, by more to notify you about flag changes on messages, and by (almost?) all to notify you that they're about to close your connection.
What can cause this to happen?
I moved my laptop to a friends house to work on this project. I opened the same port on his xfinity router, and changed all areas of my code to his IP. However it appears that the client is sending a message and the server has never getting past this part of code
System.out.println("running server!");
int nreq = 1;
try{
//SET ME PORT
ServerSocket sock = new ServerSocket(7332);
for(;;){
Socket newsock = sock.accept();
System.out.println("Creating thread...");
//Broken Old Login crap, needs reworked for map n stuff anyhow now
// Thread t = new ThreadHandler(newsock, nreq);
Thread t = new RequestInterpreter(newsock, nreq);
//t.run();
t.start();
nreq++;
}
}
catch(Exception e)
{
e.printStackTrace();
}
It never gets to print "Creating thread". I'm not sure where to begin with what could be going wrong here?
The only thing that has changed is the house, IP, router, and internet. Works everywhere else. What about those changing could block the client from sending a
Here is a test client I wrote also.
import java.io.DataInputStream;
import java.io.PrintWriter;
import java.net.Socket;
public class testClientConnection {
public static void main(String[] args) {
System.out.println("Starting testConnection");
try{
Socket s = new Socket("xx.xx.xx.xxx", 7332);
DataInputStream fromServer = new DataInputStream(s.getInputStream());
PrintWriter toServer = new PrintWriter(s.getOutputStream(), true);
toServer.println("account name");
toServer.println("password");
toServer.println("Login");
System.out.println("Sent message...");
String response = fromServer.readLine().toString();
//Toast the result here? //testing
System.out.println("response: " + response);
if (response.equals("Login Success")) {
System.out.println("Login Success!!!");
}
}
catch(Exception e){ /
}
}
}
HUGE UPDATE!
Ok so my client was an android phone and I turned the wifi off, so it fell onto 4g-LTE. Then it worked. So... Something is blocking the client side code. What might that be?
The firewall on your friend's router is the usual suspect.
Second suspect is the firewall on the target machine.
Try disabling those.
The problem will be NAT on the router.
Servers don't work behind NAT devices unless you set up port-forwarding so that the router knows where to send an incoming request from outside.
I have a server-client pair and I want to create a listener on the client end for new server responses. I am not sure how to do this, right now I can only interact in a direct synchronous way.
Here is the server:
public class TestServer {
public static void main(String[] args) throws Exception {
TestServer myServer = new TestServer();
myServer.run();
}
private void run() throws Exception {
ServerSocket mySS = new ServerSocket(4443);
while(true) {
Socket SS_accept = mySS.accept();
BufferedReader myBR = new BufferedReader(new InputStreamReader(SS_accept.getInputStream()));
String temp = myBR.readLine();
System.out.println(temp);
if (temp!=null) {
PrintStream serverPS = new PrintStream(SS_accept.getOutputStream());
serverPS.println("Response received: " + temp);
}
}
}
}
As you can see, it sends a response when it gets one. However in general I won't be sure when other servers I use send responses, so I would like to create an asynchronous listener (or at least poll the server for a response every half-second or so).
Here is what I'm trying on the client end:
protected static String getServerResponse() throws IOException {
String temp;
try {
BufferedReader clientBR = new BufferedReader(new InputStreamReader(mySocket.getInputStream()));
temp = clientBR.readLine();
} catch (Exception e) {
temp = e.toString();
}
return temp;
}
And just for reference, yes, sending over data from client to server works fine (it System.out's the data correctly). However, when I call the above function to try and retrieve the server response, it just hangs my application, which is an Android application in case that's relevant.
What I want from a function is just the ability to ask the server if it has data for me and get it, and if not, then don't crash my damn app.
On the client side create a ConnectionManager class which will handle all the socket I/O. The ConnectionManager's connect() method will create and start a new thread which will listen for server responses. As soon as it will receive a response it will notify all the ConnectionManager's registered listeners. So in order to receive asynchronously the server responses you will have to register a listener in ConnectionManager using its register(SomeListener) method.
Also, you can have a look at JBoss Netty which is an asynchronous event-driven network application framework. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.