java必学必会之网络编程

Java必学必会之网络编程攻略

一、网络基础概念

1.1 OSI七层模型

OSI七层模型是一种通用的网络协议分层模型，分为七层。自下而上分别为：物理层、数据链路层、网络层、传输层、会话层、表示层、应用层。
Java通常使用的是传输层到应用层。

1.2 TCP/IP协议

TCP/IP协议比OSI七层模型更常用。分为四层：网络接口层、网络层、传输层、应用层。
Java提供了Socket和ServerSocket两个类用于支持TCP/IP协议的网络编程。

二、Socket编程

2.1 Socket的基础

Socket是Java提供的用于实现TCP/IP协议的基础类。
客户端通过Socket连接服务端创建Socket，服务端通过调用accept()方法接受客户端的Socket连接。

示例1：客户端代码

String hostName = "localhost";
int portNumber = 5555;

try (
    Socket echoSocket = new Socket(hostName, portNumber);
    PrintWriter out =
        new PrintWriter(echoSocket.getOutputStream(), true);
    BufferedReader in =
        new BufferedReader(
            new InputStreamReader(echoSocket.getInputStream()));
    BufferedReader stdIn =
        new BufferedReader(
            new InputStreamReader(System.in))
) {
    String userInput;
    while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
        System.out.println("echo: " + in.readLine());
    }
} catch (UnknownHostException e) {
    System.err.println("Don't know about host " + hostName);
    System.exit(1);
} catch (IOException e) {
    System.err.println("Couldn't get I/O for the connection to " +
        hostName);
    System.exit(1);
}

示例2：服务端代码

int portNumber = 5555;

try (
    ServerSocket serverSocket =
        new ServerSocket(portNumber);
    Socket clientSocket = serverSocket.accept();
    PrintWriter out =
        new PrintWriter(clientSocket.getOutputStream(), true);
    BufferedReader in = new BufferedReader(
        new InputStreamReader(clientSocket.getInputStream()));
) {
    String inputLine, outputLine;
    // Initiate conversation with client
    KnockKnockProtocol kkp = new KnockKnockProtocol();
    outputLine = kkp.processInput(null);
    out.println(outputLine);

    while ((inputLine = in.readLine()) != null) {
        outputLine = kkp.processInput(inputLine);
        out.println(outputLine);
        if (outputLine.equals("Bye."))
            break;
    }
} catch (IOException e) {
    System.out.println("Exception caught when trying to listen on port "
        + portNumber + " or listening for a connection");
    System.out.println(e.getMessage());
}

2.2 Socket的高级应用

通过设置Socket的一系列参数，可以实现Socket编程的更高级应用，如服务端与多个客户端同时通信、非阻塞式通信等。

示例3：服务端同时与多个客户端通信的代码

public class MultiServer implements Runnable {
    private Socket socket;
    private ArrayList<Socket> socketList = new ArrayList<Socket>(); // 客户端List

    public MultiServer(Socket socket, ArrayList<Socket> socketList) {
        this.socket = socket;
        this.socketList = socketList;
    }

    public void run() {
        try {
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Message Received: " + inputLine);

                // 向其它客户端发送消息
                for (Socket eachSocket : socketList) {
                    if (eachSocket != socket) {
                        OutputStream outToClient = eachSocket.getOutputStream();
                        DataOutputStream out = new DataOutputStream(outToClient);
                        out.writeUTF(inputLine);
                    }
                }
            }
            // 关闭连接
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class MultiServerMain {
    public static void main(String[] args) throws IOException {
        int portNumber = 5555;
        ArrayList<Socket> socketList = new ArrayList<Socket>();

        ServerSocket serverSocket = new ServerSocket(portNumber);
        while (true) {
            Socket socket = serverSocket.accept();
            socketList.add(socket);
            new Thread(new MultiServer(socket, socketList)).start();
        }
    }
}

三、总结

本篇攻略详细介绍了Java必学必会之网络编程，包括网络基础概念、Socket编程的基础和高级应用等内容，并给出了多个示例说明。掌握这些知识，可以帮助Java开发者更好地进行网络编程。