為什么我的程序在我的服務器上運行了兩次？

Question

我正在編寫 tcp 客戶端-服務器程序。 當客戶端鍵入“Hello”時，服務器返回他當前目錄的文件和目錄列表。 當客戶端鍵入“FileDownload”時，它會從服務器下載選定的文件。
當我輸入“Hello”時它工作正常，但是當我輸入“FileDownload”時，它在服務器端運行兩次else if(received.contains("FileDownload"))塊。 因此，服務器發送了兩倍的數據，這導致了客戶端的其他問題。

這是服務器代碼：

public static void main(String[] args) throws IOException {
        
            ServerSocket servSock = new ServerSocket(1333);
            
            String received="";
            String[] s = null;
            File[] f1;
            int i=0;
            
            File f=new File(System.getProperty("user.dir"));
            f1=f.listFiles();
            
            for(File f2:f1) {
                if(f2.isDirectory())
                    System.out.println(f2.getName() + "\t<DIR>\t" + i);
                if(f2.isFile()) 
                    System.out.println(f2.getName() + "\t<FILE>\t" + i);
                i++;
            }
            
                while (true) { 
                    
                    Socket client = servSock.accept();
                    
                    InputStream in = client.getInputStream();
                    OutputStream out = client.getOutputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                    PrintWriter pw = new PrintWriter(out, true);
                    s=f.list();
                    
                    while(true) {

                        received = reader.readLine();
                        if(received.equals("END")) break;
                        
                        if(received.equals("Hello")) {
                            System.out.println("Hello-Start");

                            int length=f1.length;
                            pw.println(length);
                            i=0;
                            for(File f2:f1) {
                                if(f2.isDirectory())
                                    pw.println(f2.getName() + "\t<DIR>\t" + i);
                                if(f2.isFile()) 
                                    pw.println(f2.getName() + "\t<FILE>\t" + i);
                                i++;
                            }
                            pw.println("Options: " + "\tFileDownload <FID>" + "\tFileUpload <name>" + "\tChangeFolder <name>");
                            System.out.println("Hello-End");

                        }
                        else if(received.contains("FileDownload")) {
                            System.out.println("FileDownload-Start");

                            int j=-1;
                            try {
                                j=Integer.parseInt(received.substring(13).trim());
                            }catch(NumberFormatException e) { 
                                System.err.println("error: " + e);
                            }
                            
                            if(j>0 && j<s.length) {
                                FileInputStream fi=new FileInputStream(s[j]);
                                byte[] b=new byte[1024];
                                System.out.println("file: "+s[j]);

                                pw.println(s[j]);
                                fi.read(b,0,b.length);
                                out.write(b,0,b.length);
                                System.out.println("FileDownload-End");
                            }
                        }

這是客戶端代碼：

public static void main(String[] args) throws IOException {
        if ((args.length != 2))
        throw new IllegalArgumentException("Parameter(s): <Server> <Port>");
        
        Socket socket = new Socket(args[0], Integer.parseInt(args[1]));
        Scanner sc = new Scanner(System.in);
        InputStream in = socket.getInputStream();
        OutputStream out = socket.getOutputStream();
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        PrintWriter pw = new PrintWriter(out, true);

        
        while(true) {
            String msg="", received="";
            String length;
            
            msg = sc.nextLine();
            pw.println(msg);
            
            if(msg.equals("END")) break; 
            
                if(poraka.equals("Hello")) {
                    System.out.println();
                    length = reader.readLine();
                    for(int i=0;i<Integer.parseInt(length);i++) {
                        received = reader.readLine();
                        System.out.println(received);
                    }
                    System.out.println("\n"+reader.readLine());
                }
                else if(msg.contains("FileDownload")) {
                    System.out.println("FileDownload-Start");
                    pw.println(msg);
                    byte[] b=new byte[1024];
                    File file=new File(reader.readLine().trim());
                    System.out.println(file.getName().trim());
                    FileOutputStream fo=new FileOutputStream("D:\\Eclipse WorkSpace\\proekt\\src\\client\\"+file.getName().trim());
                    System.out.println("file: "+file.getName().trim());

                    in.read(b,0,b.length);
                    fo.write(b,0,b.length);
                    System.out.println("FileDownload-End");
                }

我找不到導致此問題的原因，因此非常感謝任何可能的幫助！

Answer 1

這是因為您的客戶端兩次請求數據：

        msg = sc.nextLine();
        pw.println(msg);  // <-- this is the first time

然后稍后

            else if(msg.contains("FileDownload")) {
                System.out.println("FileDownload-Start");
                pw.println(msg);  // <-- this is the second time