Java socket question

Question

I'm trying to write a simple server-client program, but I have a problem: I can send data from client to server, but I can't send data from the server (I can't recive it in the client) :(
So how to send data from the server, and recive it in the client?

Server:

//this is in a thread
try {
    server = new ServerSocket(1365);
} catch (IOException e) {
    e.printStackTrace();
}
while (!exit) {
    try {
        clientSocket = server.accept();
        is = new DataInputStream(clientSocket.getInputStream());
        os = new PrintStream(clientSocket.getOutputStream());
        while ((line = is.readLine()) != null) {
            System.out.println("Message from client: " + line);
            //if (line.equals("exit")) {
            //  exit = true;
            //}
            if (line.equals("say something")) {
                os.write("something".getBytes());
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        is.close();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
os.close();
}

Client:

try {
    socket = new Socket(host, 1365);
    os = new DataOutputStream(socket.getOutputStream());
    is = new DataInputStream(socket.getInputStream());
} catch (UnknownHostException e) {}
if (socket != null && os != null && is != null) {
    try {
        os.writeBytes("say something");
        //get the answer from server
        os.close();
        is.close();
        socket.close();
    } catch (IOException e) {}
}

(sorry for the long code)
Thank you in advance.

is there a specific reason why you are using DataInputStream and DataOutputStream instead of buffered character streams? — Vasil
– Vasil, Commented Apr 12, 2009 at 13:23
seems the server would only respond when "say something" is received. Could be why it isn't responding at all. also, why is your server's output stream a PrintStream? — Peter Perháč
– Peter Perháč, Commented Apr 12, 2009 at 13:32
@MasterPeter: The client is hard-coded to send "say something", so I think this is just throw away code that Jani is using to test sockets. — Bill the Lizard
– Bill the Lizard, Commented Apr 12, 2009 at 13:34
oh, yes, right, sure :) NOOOW I see... I wasn't going to spend too much time and effort on this question. Just felt like pointing out this much. — Peter Perháč
– Peter Perháč, Commented Apr 12, 2009 at 13:38

Bill the Lizard · Accepted Answer · 2009-04-12 13:49:23Z

7

Your server's OutputStream is a PrintStream, but your client's InputStream is a DataInputStream. Try changing the server to use a DataOutputStream like your client.

Even better might be to change both to use PrintWriter and BufferedReader, like the example client/server pair in Sun's Socket Tutorial.

Just to explain a little about why your code didn't work: You can think of Stream objects as filters that your data passes through. The filter changes your data, formatting it so that the matching filter at the other end can understand it. When you send data through one type of OutputStream, you should receive it at the other end with the matching InputStream.

Just as you can't store a String object in a double, or a double in a String (not without converting it), you can't send data from one type of OutputStream (in this case a PrintStream) to a different type of InputStream.

edited Apr 12, 2009 at 13:49

answered Apr 12, 2009 at 13:28

Bill the Lizard

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2 Comments

Jani Over a year ago

The program "freezed", but I read Sun's Socket Tutorial and now it's working! :)

Bill the Lizard Over a year ago

Great, I'm glad it helped. Those are some of the best programming tutorials on the 'Net (not just the Socket Tutorials, but all of Sun's Java tutorials in general).

Jani · Accepted Answer · 2009-04-13 17:20:54Z

0

I think an other problem was that I didn't send "\n" after the text, but I used readLine() method.

answered Apr 13, 2009 at 17:20

Jani

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Comments

Chochos · Accepted Answer · 2009-04-13 18:06:29Z

0

After your os.write() do os.flush(); the message is very small and maybe it's not being sent because it didn't fill the buffer.

answered Apr 13, 2009 at 18:06

Chochos

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