编写简单的TCP网络程序，掌握ServerSocket、Socket类的具体用法：编写服务器端类ServerDemo，在ServerDemo类中创建服务器端ServerSocket对象，并依次编写监听连接、获取输入流，打印读取数据，释放资源等操作。编写客户端类ClientDemo，在ClientDemo类中创建客户端Socket对象，并分别编写建立连接、获取输出流，释放资源等步骤。依次执行ServerDemo和ClientDemo类，观察命令行输出变化。

以下是一个简单的TCP网络程序示例：

ServerDemo.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerDemo {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8888);
        System.out.println("Server started.");
        while (true) {
            Socket socket = serverSocket.accept(); // 监听连接
            System.out.println("Client connected: " + socket.getInetAddress().getHostAddress());
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String data = reader.readLine(); // 获取输入流
            System.out.println("Received data: " + data);
            reader.close();
            socket.close(); // 释放资源
        }
    }
}

ClientDemo.java

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;

public class ClientDemo {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 8888); // 建立连接
        System.out.println("Connected to server.");
        PrintWriter writer = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
        writer.println("Hello server!"); // 获取输出流
        writer.flush();
        writer.close();
        socket.close(); // 释放资源
    }
}

在命令行中依次执行ServerDemo和ClientDemo，可以看到如下输出：

Server started.
Client connected: 127.0.0.1
Received data: Hello server!
Connected to server.

这表明客户端成功与服务器建立连接，并向服务器发送了一条消息。服务器成功监听到连接并读取了客户端发送的消息。