java 网络编程

 服务器端：

package abc;

import java.net.*;
import java.io.*;
import java.util.*;

public class MyServer
{
	//定义保存所有Socket的ArrayList
	public static ArrayList<Socket> socketList
		= new ArrayList<>();
	public static void main(String[] args) 
		throws IOException
	{
		ServerSocket ss = new ServerSocket(30000);
		while(true)
		{
			// 此行代码会阻塞，将一直等待别人的连接
			Socket s = ss.accept();
			socketList.add(s);
			// 每当客户端连接后启动一条ServerThread线程为将客户端发送的信息返回客户端
			new Thread(new ServerThread(s)).start();			
		}		
	}	
}

class ServerThread implements Runnable 
{
	// 定义当前线程所处理的Socket
	Socket s = null;
	// 该线程所处理的Socket所对应的输入流
	BufferedReader br = null;
	public ServerThread(Socket s)
	throws IOException
	{
		this.s = s;
		// 初始化该Socket对应的输入流
		br = new BufferedReader(new InputStreamReader(s.getInputStream()));
	}
	public void run()
	{
		try
		{
			String content = null;
			// 采用循环不断从Socket中读取客户端发送过来的数据
			while ((content = readFromClient()) != null)
			{
				// 遍历socketList中的每个Socket，
				// 将读到的内容向每个Socket发送一次
				for (Socket s : MyServer.socketList)
				{
					PrintStream ps = new PrintStream(s.getOutputStream());
					ps.println(content);
				}
			}
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
	// 定义读取客户端数据的方法
	private String readFromClient()
	{
		try
		{
			return br.readLine();
		}
		// 如果捕捉到异常，表明该Socket对应的客户端已经关闭
		catch (IOException e)
		{
			// 删除该Socket。
			MyServer.socketList.remove(s);      // ①
		}
		return null;
	}
}

客户端：

package abc;

import java.io.*;
import java.net.*;

public class MyClient
{
	public static void main(String[] args)throws Exception 
	{
		Socket s = new Socket("127.0.0.1" , 30000);
		// 客户端启动ClientThread线程不断读取来自服务器的数据
		new Thread(new ClientThread(s)).start();   // ①
		// 获取该Socket对应的输出流
		PrintStream ps = new PrintStream(s.getOutputStream());
		String line = null;
		// 不断读取键盘输入
		BufferedReader br = new BufferedReader(
			new InputStreamReader(System.in));
		while ((line = br.readLine()) != null)
		{
			// 将用户的键盘输入内容写入Socket对应的输出流
			ps.println(line);
		}
	}
}


class ClientThread implements Runnable
{
	// 该线程负责处理的Socket
	private Socket s;
	// 该线程所处理的Socket所对应的输入流
	BufferedReader br = null;
	public ClientThread(Socket s)
		throws IOException
	{
		this.s = s;
		br = new BufferedReader(
			new InputStreamReader(s.getInputStream()));
	}
	public void run()
	{
		try
		{
			String content = null;
			// 不断读取Socket输入流中的内容，并将这些内容打印输出
			while ((content = br.readLine()) != null)
			{
				System.out.println(content);
			}
		}
		catch (Exception e)
		{
			e.printStackTrace();
		}
	}
}