Question

I have a third party server which I can connect to (on my local network) to do some neat things I need to do for a project I am working on. I use a Java library provided by the third party to o all of the connection stuff, and I can successfully send commands to the server using their code. Their code also provides some event listener interfaces which I am able to implement in order to get status changes from the server, as long as my program is running. What I would like to do is create a program which will just run as (or like) a service listening perpetually from events on the server and writing them to a database, but I also need to be able to listen for connections from my local machine so I can use a command line program to tell my service to send messages to the server (the server only allows one connection at a time).

I have looked (briefly) at JMS as well as RMI, but they both seem like they may be much more complicated and heavyweight than what I think I need to communicate locally. Is there a method that is simpler for sending simple messages (and by simple I mean a single pipe delimited string would do the trick) between two running applications on the same machine?

Answer 1

You could use sockets for interprocess communication if you want something simpler than RMI and JMS.

The java tutorial on sockets might be a good place to start.

A simple one message client-server where the server waits until a client joins and then receives a message from the client could look like this:

public class SocketsServer {

    public static void main(String[]rags) throws Exception
    {
        ServerSocket ss1 = new ServerSocket();
        ss1.bind(new InetSocketAddress("localhost",9992));
        //accept blocks until someone connects
        Socket s1 = ss1.accept();
        BufferedReader br = new BufferedReader(new InputStreamReader(s1.getInputStream()));
        String line;
        while( (line = br.readLine()) != null )
        {
            System.out.println(line);
        }
        s1.close();
        ss1.close();
    }
}

And for Client side:

public class SocketsClient {

    public static void main(String[]args) throws Exception
    {
        Socket ss = new Socket();
        ss.connect(new InetSocketAddress("localhost", 9992));
        PrintWriter pw = new PrintWriter(ss.getOutputStream(), true);
        pw.println("hello socket");
        ss.close();
    }
}