CODEWITHSUNDEEP
javasocketsnetwork-programmingchatprotocols
JumbleGee
JumbleGee

Reputation: 85

How could I identify multiple commands for network application (Java)

I want to build a client-server-application for some practice. I started off with a simple chat which was not so hard to do. I'm also able to identify different commands by just simply split a String, e.g. "command:msg". But I think that may be a little inconvenient. So I'm wondering if there are better ways to realize that. And I stumbled over that side: http://www.javaworld.com/jw-01-1997/jw-01-chat.html?page=6 At the very end it says:

An alternative, however, and much more elegant solution, is to abstract the protocol behind a set of stream classes. The specifics of header construction and insertion can be handled automatically by the stream classes, and the client is then left with much the same interface as before: Clients write messages to a stream, but instead of flushing the stream, they call a method that attaches appropriate headers and sends the encapsulated message.

I don't really know what is meant by that. Could somebody explain it, or even better, give me a code example. Perhaps there may are other ways to do?

Upvotes: 2

Views: 197

Answers (2)

Jean Waghetti
Jean Waghetti

Reputation: 4727

Let's say you want to send messages encapsulated as the link you sent:

| ID | len | message contents |.

What they mean with "to abstract the protocol behind a set of stream classes" is to create classes that extend stream classes which will put the correct ID and length on the encapsulated message for you.

For example, for an extended PrintWriter where you send two kinds of message:

ID 1 - normal message.

ID 2 - error message.

class MyProtocolPrintWriter extends PrintWriter {

    public static final int NORMAL_MESSAGE = 1;
    public static final int ERROR_MESSAGE = 2;

    //put the constructor

    public void writeMessage(String message) {
        println(
            String.format(
            "%02x%02d%s", NORMAL_MESSAGE, message.length(), message));
    }

    public void writeErrorMessage(String message) {
        println(
            String.format(
            "%02x%02d%s", ERROR_MESSAGE, message.length(), message));
    }

}

Upvotes: 1

Gilbert Le Blanc
Gilbert Le Blanc

Reputation: 51515

Here's what one fairly successful chat network used for a protocol.

Internet Relay Chat

And here's a list of the commands that were implemented using the IRC protocol.

List of Internet Relay Chat commands

You would implement these commands as a set of stream classes. The user issues a command, and your stream class handles the specifics of the header construction and insertion into the stream.

Upvotes: 0

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