I want to create a simple chat program. But my requirement is some what different I want a single client - server type of thing. Means I don't want a multiple client server.
I am creating a server and waiting for client to connect. After client connects I am waiting for any message from client.
Now my problem is that when I run my client program, I can run multiple instances of it, but the only first client messages are delivered to server as it is single server client program. What I want is some sort of method with which I can limit other clients to connect and say display error message saying that server is busy try after sometime. Can anyone help me do that?
The server should have a list of all client connected so whenever a new client connect; instead of just adding a new client; it check if there is already a user connected and if yes ; it close the connection/return special exception.It is up to the client project you made that decide how it will handle this closing of connection/exception.
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So basically I'm doing a server and client in java.
In order for it to run, I have to run both a client.java and server.java. I need to close one or both depending on the instance
What I currently need is a way such that when the client passes a parameter x, the client should close but the server should remain open. I also have to implement it in such a way that if client passes parameter y instead, both the client and server should close
I thought of doing:
System.exit(0);
But I'm not sure if this would close both server and client, meaning that it would be useful for the second instance. I also thought of just letting it reach the end of the program, but I'm not really sure what result would be the result of that.
If you want the server to keep listening for more requests for a handshake (even when previous connections terminate), what you need is a multi-client server. A server that can handle multiple clients usually runs a thread that keeps looping and listens for a client that wants to connect. Such a thread would generate a new thread for each connection and store it in an array of threads that all keep listening or talking with each client.
You can learn more about multiple client servers here.
With the array of threads listening to all clients, you could assign a condition that terminates all threads and connections in the server. This could be a String that one of the clients can relay to the server, such as "/exit" and the server can check if information sent by any client-thread is "/exit".
I am completely new to creating a network connection in java so I apologize if this is a stupid question.
I am trying to create a D&D companion in java that will allow a player to create their character and then send it to the DM so that they can view it and make changes and send it back to the player. I want to be able to make it so that any time a field is changed on one computer it will also be changed on the other computer.
After a bunch of research online I have been able to create a socket connection between the DM(server) and the player(client) and pass a message between the two but I am not sure how a socket connection works after this initial connection is made. My research has not been very clear on this. I have found many resources that have said that java closes the socket after a message has been passed and many that say that the socket stays open.
If java closes the socket then my problem is easy enough to solve because then I will just have to open a new socket every time I need to pass data making sure that I pass the IP address of the client to the server the first time I make a connection.
My real questions come in when a socket stays open.
If the socket stays open and multiple clients connect to the server, will the server just shout over the network whenever it transmits a message so that all clients receive the message? (If this is the case then I know I can just attach a username to the front of the message so that the client can determine if the server is talking to it.)
If the server does not shout then how do I specify which client I want the server to talk to?
Will I have to add a loop to my receive methods so that the client/server is constantly listening for a transmission from the server/client or will java automatically do so after I run the method the first time?
I have found many resources that have said that java closes the socket after a message has been passed
You found them where?
and many that say that the socket stays open.
All those are correct. Java never closes connections. The application closes connections.
If java closes the socket then my problem is easy enough to solve because then I will just have to open a new socket every time I need to pass data making sure that I pass the IP address of the client to the server the first time I make a connection.
It doesn't.
My real questions come in when a socket stays open.
If the socket stays open and multiple clients connect to the server, will the server just shout over the network whenever it transmits a message so that all clients receive the message?
No. It will respond via the socket that is connected to the corresponding client.
(If this is the case then I know I can just attach a username to the front of the message so that the client can determine if the server is talking to it.)
Unnecessary.
If the server does not shout then how do I specify which client I want the server to talk to?
The server responds via the same socket it read the request from.
Will I have to add a loop to my receive methods so that the client/server is constantly listening for a transmission from the server/client
No, you will have to add a thread per accepted socket, that loops reading requests until end of stream.
or will java automatically do so after I run the method the first time?
No.
You seem to have been reading some truly appalling drivel. Take a look at the Custom Networking section of the Java Tutorial.
Adding to EJP's wise answer, it might be worth clarifying:
Sounds like you (wisely) use TCP, so your Socket represents a connection between 1 server and 1 client. No "shouting". In examples such as this , when connection is established (namely, client obtains a Socket by calling "new Socket" and server obtains a Socket by calling "accept"), those Sockets are dedicated to those 2 specific endpoints. So if 10 clients connect to 1 server, the server will keep 10 Sockets and won't mix them up. A bit like a poor secretary that has 10 phones on his desk and answers them all - despite the mess, each earpiece is clearly connected to 1 customer.
The connection can hold for a while & serve several messages. It will terminate when either one of the sides calls 'socket.close', or it can be terminated by underlying 3rd parties (operating system, proxies, firewalls).
For your first version, or for simple business requirements, it's probably enough to converse over this 1 simple connection. However, for commercial critical data that requires 'assurance of delivery', you might need to invest some careful thought & possibly tools such as RabbitMQ.
Good luck:)
I have a spreadsheet application in Java, and one of the features it provides (which I developed) is sheet sharing. Basically, anyone can be a client or a server because the app has both server and client code. The user who is the server creates the share, specifies the IP, and then the share is created and active (best case scenario) with the server listening for clients on its IP and selected port.
At the moment, the client needs to enter the IP and port of the server that's listening in order to connect. The server then creates a new socket for that client and communicates with in on a separate thread, while the server continues listening on another (traditional TCP behavior). This is all working fine.
What I need to develop is auto-discovery, e.g. a client does not need to type in an IP or port, they simply select 'Join a share...' from the menu and then it starts looking for servers. When one is found, it should send its list of active shares on that IP. The user then selects which share to join from the list, and is connected.
However, I have doubts on how to tackle this issue. Should I use broadcast to poll servers, like DHCP does? Or is there an easier way?
What I'd like to implement is:
Client -> polls local network -> finds a server -> server sends active share list to client -> client selects share to join -> connected!
Technically, what you're looking for is active servers that are running your spreadsheet application.
One possibility would be for your server code to send out an "alive" message to the network every so often (say every 15 seconds). Your client code would listen for these "alive" messages, and produce a meaningful list of spreadsheet servers.
Another possibility would to to use the same database engine that you're using to store the spreadsheets to store the IP and port of the connected server code. The client code would just read the database table to get the connections.
I have created this game bot where it connects to the game, and starts playing.
My problem is that i can't start more than one of these as the other then won't work.
Is is possible that if i run 2 instances of the same program the sockets are interfering with each other ? After all, they do connect to the same IP with the same port ?
And sometimes after i close(just closing cmd) the program is unable to connect again. Is that cause i didn't close the connections right ?.
I hope this is enough else i'll just have to post my source code
Best regards.
It's possible to connect to the same socket/port several times. Actually a socket is a double peer: {client ip/ client port}{server ip/server port}. When you connect to a server, your client port is assigned dynamically. You will have a new and different client port per client. So it should work unless the server side forbid it.
You should have a server that listens for multiple connections. A server is bound to a port and once that port is in use another application cannot use it. So for the server just have one instance. Multiple clients can connect to this IP/Port as long as the Server accepts multiple connections.
If a client connects to the server and the other clients stop working this may be because the server does not support multiple clients. To do this you need to use multi threading in the server. The server should accept a client socket and create a new instance of a client with it's own StreamReader/Writer objects.
http://tutorials.jenkov.com/java-multithreaded-servers/multithreaded-server.html
if you are working with a specific TCP port, then there is a close-wait period that this port cannot be claimed temporariliy for some time. also multiple programs cannot listen the same TCP port. Use threads.
I am trying to write a piece of software that
accept simple UDP messages (text strings) from simple UDP client,
opens connection to another server and forwards messages to it
listens for that server reply and
forwards that reply back to the client.
So it is a simple intermediate server.
To visualise the communication:
Client <---> Intermediate Server <---> "Real" Server
The client connects to the Intermediate but has no idea that the message it sends is being forwarded to another server, or that it's reply is actually from another server. As far as the client cares it the Intermediate server is the real server.
I am trying to use Java's DatagramChannel for this, but not quite sure how to correctly do this in a non-hack way. Do I use two DatagramChannels? One for Client--Intermediate and the other for Intermediate--Real Server?
An general outline of approach would be appreciated, particularly if I need to open a socket every time I need to forward a message from the Intermediate to the Real Server, or if I can keep that socket open somehow.
You only need one datagram socket for this, and you can keep it open for the life of the process.