改写socket服务器端程序（即实验1中参考example11-5中server.java的编程结果），设计编写出一个TCP服务器端程序：要求使用线程池处理客户端的连接请求。相应需修改socket客户端程序：从本地一个txt文件（注意：客户端的此txt文件称为信源txt文件，该txt测试数据文件可自由选择或创建，只要里面包含至少10行字符串即可），逐行读取出来，每一行作为一句话，发送给服务器，服务器每收到一个客户端的一句话，就将其保存在服务器本地的一个专用于存放与该客户端通信内容的txt文件中（注意：称为通信记录txt文件，来自不同的客户端的信息需保存在不同的txt文件中，需多少个txt文件应在程序中自动根据实际连接的客户端数量自动创建），服务器还会计算每一个通信记录txt文件的安全算法摘要，将安全算法摘要和该通信记录txt文件名一起写入到服务器中一个名为SafeAbstract.txt的文件中。

TCP服务器端程序：

import java.io.*;
import java.net.*;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Server {
    private static final int PORT = 8888;
    private static ExecutorService executorService = Executors.newCachedThreadPool();

    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(PORT);
            System.out.println("Server started.");
            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("Client connected: " + socket.getInetAddress().getHostAddress());

                executorService.execute(new ClientHandler(socket));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static class ClientHandler implements Runnable {
        private Socket socket;

        public ClientHandler(Socket socket) {
            this.socket = socket;
        }

        @Override
        public void run() {
            try {
                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String line;
                String fileName = socket.getInetAddress().getHostAddress() + ".txt";
                PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(fileName, true)));
                while ((line = in.readLine()) != null) {
                    out.println(line);
                    out.flush();
                }
                out.close();
                in.close();
                socket.close();

                writeSafeAbstract(fileName);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        private void writeSafeAbstract(String fileName) {
            try {
                MessageDigest md5 = MessageDigest.getInstance("MD5");
                FileInputStream fis = new FileInputStream(fileName);
                byte[] buffer = new byte[1024];
                int length;
                while ((length = fis.read(buffer)) != -1) {
                    md5.update(buffer, 0, length);
                }
                fis.close();

                byte[] digest = md5.digest();
                StringBuilder sb = new StringBuilder();
                for (byte b : digest) {
                    sb.append(String.format("%02x", b));
                }
                String safeAbstract = sb.toString();

                PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("SafeAbstract.txt", true)));
                out.println(fileName + " " + safeAbstract);
                out.flush();
                out.close();
            } catch (NoSuchAlgorithmException | IOException e) {
                e.printStackTrace();
            }
        }
    }
}

TCP客户端程序：

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

public class Client {
    private static final String FILENAME = "source.txt";
    private static final String SERVER_IP = "127.0.0.1";
    private static final int SERVER_PORT = 8888;

    public static void main(String[] args) {
        try {
            BufferedReader in = new BufferedReader(new FileReader(FILENAME));
            Socket socket = new Socket(SERVER_IP, SERVER_PORT);
            PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())));

            String line;
            while ((line = in.readLine()) != null) {
                out.println(line);
                out.flush();
            }
            out.close();
            in.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}