import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
/**
 * Server类接收客户端的套接字请求，然后创建一个ServerThread线程来处理请求
 * @author Administration
 *
 */
public class Server {
    public static void main(String[] args) {
        System.out.println("等待连接。。。");
        try {
            //1.创建一个套接字对象serverSocket，设置端口号为6666
            ServerSocket serverSocket = new ServerSocket(6666);
            Socket clientSocket = null;
            //2.监听套接字响应，一旦获得相应，则新建一个Serverhread类来处理这个响应
            while(true) {
                clientSocket = serverSocket.accept();//监听
                new ServerThread(clientSocket);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;

public class ServerThread extends Thread {
    //客户端靠套接字
    private Socket clientSocket = null;
    //客户端输入流
    private InputStream clientInput = null;
    //客户端输出流
    private OutputStream clientOutput = null;
    
    //1.首先从构造方法中获得客户端的套接字请求，创建向客户端输入和输出的流，启动线程指执行接下来的请求
    public ServerThread(Socket socket) throws IOException {
        clientSocket = socket;
        clientInput = clientSocket.getInputStream();
        clientOutput = clientSocket.getOutputStream();
        this.start();
    }

    //2.线程启动后，通过缓冲流来获取从客户端传来的数据并进行分析，如果传过来的是“over”，则终止线程并关闭端口；
    //反之，则计算从客户端传过来的数值对应于正方形边长的面积，并将返回结果返回客户端，之后关闭端口
    public void run() {
        
        try {
            //构建缓冲输入流，获取客户端传过来的数据
            BufferedReader bufReader = new BufferedReader(new InputStreamReader(clientInput));
            //按行读取输入流内容（数据）
            String strLine = bufReader.readLine();
            
            //判断输入流数据
            if("OVER".equalsIgnoreCase(strLine)) {
                //创建输出流，传递“over”信息，表示连接结束
                PrintWriter printWriter = new PrintWriter(clientOutput,true);
                printWriter.println("连接OVER");
            }else {
                //输入正方形边长，并输出边长及面积
                double side = Double.parseDouble(strLine);
                side = Double.parseDouble(strLine);
                System.out.println("Side of Square Received:"+side);
                double squareArea = side*side;
                String str = "Side:"+side+"Square:"+squareArea;
                //创建输出流向客户端传递运算结果
                PrintWriter printWriter = new PrintWriter(clientOutput,true);
                printWriter.println(str);
                System.out.println("Finish sending to client!");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //关闭流和端口
            try {
                clientInput.close();
                clientOutput.close();
                clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        
    }
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

/**
 * 客户端类
 * @author Administration
 *
 */

public class Client {
    public static void main(String[] args) {
        Socket socket = null;
        try {
            //1.根据端口号创建与服务器端的连接
            socket = new Socket("127.0.0.1",6666);
            
            //2.客户端从获取用户在控制台输入的信息
            //通过Scanner获取键盘输入的值
            System.out.println("Input Side:");
            Scanner keyInput = new Scanner(System.in);
            //按行读取键盘输入
            String strLine = keyInput.nextLine();
            
            //3.创建客户端的输入流和输出流，将用户输入的信息发送到服务器端，之后再接收来自服务器端的运算结果
            //获取服务器输入流
            OutputStream outputStream = socket.getOutputStream();
            //获取服务器输出流
            InputStream inputStream = socket.getInputStream();
            //通过PrintWriter输出流向服务器传数据
            PrintWriter printWriter = new PrintWriter(outputStream,true);
            printWriter.println(strLine);
            BufferedReader bufdReader = new BufferedReader(new InputStreamReader(inputStream));
            System.out.println(bufdReader.readLine());
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                //4.关闭套接字和流
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        
    }
}

等待连接。。。
Side of Square Received:5.0
Finish sending to client!

Input Side:
5
Side:5.0 Square:25.0