Java programming steps to implement small local area network chat application

开发环境：

IDEA 2018.2 集成开发工具。

实现功能：

1、用户上线，向服务器通知并注册。

2、同局域网下，所有注册用户可以进行群聊。

3、同局域网下，所有用户可与任意已注册用户进行私聊。

4、用户下线，通知服务器，服务器更新信息。

实现原理：

1、服务器端实例化一个ServerSocket对象，调用accept方法等待客户端连接到服务器。

2、客户端实例化 Socket 对象，并使用构造方法与服务器建立链接。

3、服务器端根据客户端输入信息，辨别客户端请求的功能从而做出相应响应。

实用技术：

为了能够高效的处理客户端的请求，在服务器端使用多线程处理客户端请求。并且使用 ConcurrentHashMap 来存储所有注册过的客户端。

项目源码（解释写在代码的注释当中）：

服务器端：

import java.io.IOException;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
import java.util.concurrent.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class ManyThreadServer {
    //存储所有注册的客户端
    private static Map<String, Socket> clientMap = new ConcurrentHashMap<String,Socket>();
    //具体的处理每个客户端的请求
    private static class ExcuteClient implements Runnable{
        private Socket client;
        public ExcuteClient(Socket client) {
            this.client = client;
        }
        @Override
        public void run() {
            try {
                //获取客户端的输出流，读取客户端消息，并处理
                Scanner in = new Scanner(client.getInputStream());
                String strFromClient;
                while(true){
                    if(in.hasNextLine()){
                        strFromClient = in.nextLine();
                        //在Windows下默认换行是：\r\n,所以把\r要转换为空字符串
                        Pattern pattern = Pattern.compile("\r");
                        Matcher matcher = pattern.matcher(strFromClient);
                        strFromClient = matcher.replaceAll("");
                        //注册流程
                        if(strFromClient.startsWith("useName")){
                            String useName = strFromClient.split("\\:")[1];
                            registerUser(useName,client);
                            continue;
                        }
                        //群聊功能
                        if(strFromClient.startsWith("G")){
                            String msg = strFromClient.split("\\:")[1];
                            groupChat(msg,client);
                            continue;
                        }
                        //私聊功能
                        if(strFromClient.startsWith("P")){
                            String userName = strFromClient.split("\\:")[1].split("-")[0];
                            String msg = strFromClient.split("\\:")[1].split("-")[1];
                            privateChat(userName,msg,client);
                            continue;
                        }
                        //用户退出
                        if(strFromClient.startsWith("B")){
                            String userName = null;
                            //根据Socket找到UserName
                            for(String keyName : clientMap.keySet()){
                                if(clientMap.get(keyName).equals(client)){
                                    userName = keyName;
                                }
                            }
                            System.out.println("用户" + userName + "下线了。。。");
                            clientMap.remove(userName);
                            System.out.println("当前共有用户" + clientMap.size() + "人");
                            continue;
                        }
                        else{
                            PrintStream out = new PrintStream(client.getOutputStream(),true,"UTF-8");
                            out.println("输入错误。。。");
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        private void registerUser(String name,Socket client){
            System.out.println("用户：" + name + "已上线！");
            clientMap.put(name,client);
            System.out.println("当前在线人数：" + clientMap.size() + "人！");
            //既然是用户在注册，所以这里服务器通知用户注册结果
            try {
                PrintStream out = new PrintStream(client.getOutputStream(),true,"UTF-8");
                out.println("用户注册成功！");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        private void groupChat(String msg,Socket client){
            //取出clientMap中所有的Entry对象，遍历每个用户，并且发送消息
            Set<Map.Entry<String,Socket>> clientSet = clientMap.entrySet();
            for(Map.Entry<String,Socket> entry:clientSet){
                try {
                    Socket socket = entry.getValue();
                    //取得输出流，向客户端发送消息
                    PrintStream out = new PrintStream(socket.getOutputStream(),true,"UTF-8");
                    out.println("由端口号为"+ client.getPort() + "发来的群聊消息：" + msg);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        private void privateChat(String userName,String msg,Socket client){
            Socket privateSocket = clientMap.get(userName);
            try {
                PrintStream out = new PrintStream(privateSocket.getOutputStream(),true,"UTF-8");
                out.println("由端口号为：" + client.getPort() + "发来的消息：" + msg);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args)throws Exception{
        //为了提高效率，这里使用多线程进行处理
        ExecutorService executorService = Executors.newFixedThreadPool(30);
        //实例化ServerSocket对象，并指定IP为本地主机，端口号为6666
        ServerSocket serverSocket = new ServerSocket(6666);
        for(int i = 0; i < 30;i++){
            System.out.println("等待用户连接。。。");
            //等待客户端连接服务器
            Socket client = serverSocket.accept();
            System.out.println("有客户端连接，端口号为：" + client.getPort());
            //启动线程，并处理客户端请求
            executorService.submit(new ExcuteClient(client));
        }
        //关闭线程，关闭服务器
        executorService.shutdown();
        serverSocket.close();
    }
}

客户端：

import java.io.IOException;
import java.io.PrintStream;
import java.net.Socket;
import java.util.Scanner;
 
/**
 *  接收服务端发来的消息
 */
class FromServer implements Runnable{
    Socket client;
    public FromServer(Socket client){
        this.client = client;
    }
    @Override
    public void run() {
        try {
            Scanner in = new Scanner(client.getInputStream());
            while (true) {
                if (in.hasNextLine()) {
                    System.out.println("服务器：" + in.nextLine());
                }
                //判断客户端是否退出，如果推出，跳出循环，并关闭流
                if (client.isClosed()) {
                    System.out.println("客户端关闭。。。");
                    break;
                }
            }
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
 
/**
 *  向服务端发出消息
 */
class ToServer  implements Runnable{
    Socket client;
    public ToServer(Socket client){
        this.client = client;
    }
    @Override
    public void run() {
        try {
            Scanner scanner = new Scanner(System.in);
            PrintStream out = new PrintStream(client.getOutputStream(),true,"UTF-8");
            while (true) {
                System.out.println("请输入信息：");
                String strToserver;
                if(scanner.hasNextLine()){
                    strToserver = scanner.nextLine().trim();
                    out.println(strToserver);
                    //客户端退出标志：B
                    if(strToserver.startsWith("B")){
                        System.out.println("客户端退出。。。");
                        scanner.close();
                        out.close();
                        client.close();
                        break;
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
public class ManyThreadClient {
    public static void main(String[] args){
        try {
            //实例化Socket对象，与服务器建立连接
            Socket client = new Socket("127.0.0.1",6666);
            //为了发送消息和接收消息可以同时进行，使用多线程进行处理
            Thread thread1 = new Thread(new FromServer(client));
            Thread thread2 = new Thread(new ToServer(client));
            thread1.start();
            thread2.start();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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