2. Java Socket

在Java中，套接字实现类为SocketImpl（抽象基类），包含所有的套接字通信方法。
编程接口为ServerSocket（服务器）和Socket（客户端），内含SocketImpl实例，根据角色调用真正的套接字方法。

• SocketImpl

// 创建套接字：流式/数据报
void create(boolean stream);

// 绑定本地IP地址和端口
void bind(InetAddress host, int port);

// 监听请求
void listen(int backlog);

// 请求连接
void connect(InetAddress address, int port);

// 接受连接
void accept(SocketImpl s);

// 通过输出流发送消息
OutputStream getOutputStream();
void shutdownOutput();

// 通过输入流读取消息
InputStream getInputStream();
void shutdownInput();

// 关闭套接字
void close();

• ServerSocket

// 创建套接字、绑定本地端口、监听连接请求
ServerSocket(int port);

// 阻塞直到建立连接
// 返回：与客户端通信的Socket实例
Socket accept();

// 关闭套接字
void close();

• Socket

// 创建套接字、请求远程套接字，阻塞直到建立连接
Socket(String host, int port)

// 通过输出流发送消息
OutputStream getOutputStream();
// 关闭发送
void shutdownOutput();

// 通过输入流读取消息
InputStream getInputStream();
// 关闭读取
void shutdownInput();

// 关闭套接字
void close();

• 示例代码：

  • 服务器：

int port = 8000;
ServerSocket serverSocket = null;
try {
    serverSocket = new ServerSocket(port);
    System.out.println("服务器监听：" + port);

    for (int i = 0; i < 3; i++) {
        Socket socket = serverSocket.accept();
        System.out.println("\n服务器建立连接：" +
                "本地（" + socket.getLocalAddress().getHostAddress() + ":" + socket.getLocalPort() + "），" +
                "远程（" + socket.getInetAddress().getHostAddress() + ":" + socket.getPort() + "）");

        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"));
        BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));

        String line = reader.readLine();
        System.out.println("他：" + line);

        line = "你好，我是服务器！\n";
        System.out.print("我：" + line);
        writer.write(line);
        writer.flush();

        while (true) {
            line = reader.readLine();
            if (line == null) {
                break;
            }
            System.out.println("他：" + line);
        }
        socket.shutdownInput();

        line = "再见，客户端！\n";
        System.out.print("我：" + line);
        writer.write(line);
        writer.flush();
        socket.shutdownOutput();

        socket.close();
    }
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (serverSocket != null) {
        try {
            serverSocket.close();
            System.out.println("\n服务器关闭");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

• 客户端：

String host = "127.0.0.1";
int port = 8000;
Socket socket = null;
try {
    socket = new Socket();
    socket.connect(new InetSocketAddress(host, port));
    System.out.println("客户端建立连接：" +
            "本地（" + socket.getLocalAddress().getHostAddress() + ":" + socket.getLocalPort() + "），" +
            "远程（" + socket.getInetAddress().getHostAddress() + ":" + socket.getPort() + "）");

    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"));
    BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));

    String line = "你好，我是客户端！\n";
    System.out.print("我：" + line);
    writer.write(line);
    writer.flush();

    line = reader.readLine();
    System.out.println("他：" + line);

    for (int i = 1; i <= 3; i++) {
        line = "第" + i + "句。\n";
        System.out.print("我：" + line);
        writer.write(line);
        writer.flush();
    }

    line = "再见，服务器！\n";
    System.out.print("我：" + line);
    writer.write(line);
    writer.flush();
    socket.shutdownOutput();

    line = reader.readLine();
    System.out.println("他：" + line);
    socket.shutdownInput();

    socket.close();

} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (socket != null) {
        try {
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}