java - 多线程，Java 服务器/客户端项目

Question

嗨，我目前正在使用 Java 开发服务器/客户端程序，其中客户端连接到服务器并向服务器发送一个数字，然后服务器将此数字添加到全局变量并返回全局变量。我遇到的问题是，当我有多个客户端时，一个客户端无法工作，而另一个客户端可以工作，稍后创建的客户端可以工作。我为每个客户端创建了单独的线程，并且在一定程度上起作用。

这是创建新线程的服务器类的片段

public static Integer globalSum = 0;

public static void main(String[] args) throws IOException
{

    ServerSocket server = new ServerSocket(8888);
    Socket s;

    System.out.println("Server running. Waiting for a client to connect...");

    while(true) {

        s = server.accept();
        ThreadHandler th=new ThreadHandler(s);
        Thread t=new Thread(th);
        t.start();
        System.out.println("Client is now connected");

    }
}

这是我的客户类

public class Client2 {

    public static void main(String[] args) throws IOException {
        Socket s = new Socket("localhost", 8888);
        InputStream instream = s.getInputStream();
        OutputStream outstream = s.getOutputStream();
        Scanner in = new Scanner(instream);
        Scanner input= new Scanner(System.in);
        PrintWriter out = new PrintWriter(outstream);

        for(int i=0;i<5;i++){
            System.out.println("Please enter a value "+(i+1));
            String response=input.nextLine();
            String request="SUBMIT"+" "+response+"\n";
            out.print(request);
            out.flush();
            System.out.println(in.nextLine());
        }

        out.print("QUIT\n");
        out.flush();

        s.close();
    }

}

这是我的 ThreadHandler 类

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Scanner;

public class ThreadHandler implements Runnable {

    private Socket s;
    private Scanner in;
    private static PrintWriter out;
    ServerMultipleClients serverInstance;

    public ThreadHandler(Socket s)
    {
        //this.serverInstance=serverInstance;
        this.s=s;

    }

    public void run() {
        try {
            try {

                in = new Scanner(s.getInputStream());
                out = new PrintWriter(s.getOutputStream());

                doService(); // the actual service

            } finally {
                s.close();
            }

        } catch (IOException e) {
            System.err.println(e);
        }
        return;
    }


    public void doService() throws IOException{

        String request;

        while(true){

            request=in.next();
            String arrayString[] = request.split("\\s+") ;
            if(request.equals("SUBMIT")){
                String value2=in.next();
                handle(value2);
            }
            else if (request.equals("QUIT")){
                break;
            }
            else if(!request.equals("SUBMIT")||!request.equals("QUIT")){
                System.out.println("ERROR in input");
                break;
            }

        }

    }


    public void handle(String value1){

        if(isInt(value1)==true){

            int valueInt=Integer.parseInt(value1);

            synchronized(serverInstance.globalSum) {

                if((valueInt+serverInstance.globalSum)<Integer.MAX_VALUE){
                    ServerMultipleClients.globalSum=ServerMultipleClients.globalSum+valueInt;
                    out.println("OK");
                    out.flush();
                    System.out.println("New Value for Global Sum is: "+ServerMultipleClients.globalSum);
                }
                else if((valueInt+ServerMultipleClients.globalSum)>=Integer.MAX_VALUE){
                    out.println("ERROR");
                    System.out.println("Global Sum is unchanged, its value is: "+ServerMultipleClients.globalSum);
                }
                else{
                    out.println("ERROR");
                    System.out.println("Global Sum is unchanged, its value is: "+ServerMultipleClients.globalSum);
                }

            }
        }
    }

    public boolean isInt( String input ) {
        try {
            Integer.parseInt( input );
            return true;
        }
        catch( Exception e ) {
            return false;
        }
    }

}

问题是，当我运行它时，它适用于在稍后阶段运行的每个客户端到前一个客户端，返回到前一个客户端意味着该客户端崩溃。

Answer 1

你确定这件事吗:

private static PrintWriter out;

必须是静态的吗？这意味着所有线程共享您的输出流!