卡在readLine（）上，即使該行為空

Question

我在服務器中編寫了這個循環，他只是在其中向客戶端發送一些字符串：

PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
for (int j = 0; j < i; j++) {
    out.println(tmp[j]); // send the strings to the client
}

客戶端還有另一個循環來檢索所有這些字符串，但從不退出。 例如，如果我給他發送4個字符串，則輸出將是：
-hi
-怎么樣
-是
-您
然后，在最后一個字符串之后，它掛起了，除了關閉服務器，我無法做其他任何事情。 當我關閉它時，客戶端從那一刻退出。 這是無效的循環：

        /* PHASE 2: The client receives the ArrayList with the emails */
        BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
        String line;
        String message[] = new String[5];
        for (int j=0; ((line = in.readLine()) != null) && (line.length())>0;) {
           System.out.println(line); //DEBUG
           message[j++] = line;
           if (j==5) {
                data = format.parse(message[3]);
                email.add(new Email((Integer.parseInt(message[0])), message[1], account, message[2], message[4], data));
                j=0;
            }
        }
        System.out.println("Out");

這是帶有循環的客戶端代碼：

public void loadData() throws IOException, ClassNotFoundException, ParseException {

    try {
        connect();
        ArrayList<Email> email = new ArrayList<Email>();
        DateFormat format = new SimpleDateFormat("dd/MM/yyyy");
        Date data;

        /* PHASE 1: The client sends a string to the server */
        try {
            PrintWriter out = new PrintWriter(s.getOutputStream(), true);
            out.println(account+"\n"); // send the account name to server

            /* PHASE 2: The client receives the ArrayList with the emails */
            BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
            String line;
            String message[] = new String[5];
            for (int j=0; ((line = in.readLine()) != null) && (line.length())>0;) {
                System.out.println(line); //DEBUG
                message[j++] = line;
                if (j==5) {
                    data = format.parse(message[3]);
                    email.add(new Email((Integer.parseInt(message[0])), message[1], account, message[2], message[4], data));
                    j=0;
                }
            }
            System.out.println("Out");

這是服務器代碼：

class ThreadedEchoHandler implements Runnable {

    private Socket incoming;

    private String nomeAccount = "";

    public void run() {
        try {
            incoming = s.accept();
        } catch (IOException ex) {
            System.out.println("Unable to accept requests");
        }
        contenutoTextArea.append("Connected from: " + incoming.getLocalAddress() + "\n");
        textarea.setText(contenutoTextArea.toString());
        try {
            //PHASE 1: The server receives the email
            try {
                BufferedReader in = new BufferedReader(new InputStreamReader(incoming.getInputStream()));
                nomeAccount = in.readLine();
            } catch (IOException ex) {
                System.out.println("Not works");
            }

            //PHASE 2: I'm getting all the emails from the files
            File dir = new File("src/server/" + nomeAccount);
            String[] tmp = new String[100];
            int i = 0;
            for (File file : dir.listFiles()) {
                if (file.isFile() && !(file.getName().equals(".DS_Store"))) {
                    try (BufferedReader br = new BufferedReader(new FileReader(file))) {
                        String line;
                        while ((line = br.readLine()) != null) {
                            tmp[i++] = line;
                        }
                        br.close();
                    } catch (IOException ex) {
                        System.out.println("Cannot read from file");
                    }
                }
            }

            //PHASE 3: The server sends the ArrayList to the client
            PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
            for (int j = 0; j < i; j++) {
                out.println(tmp[j]); // send the strings to the client
            }

        } catch (IOException ex) {
            System.out.println("Cannot send the strings to the client");
        }

        //PHASE 4: Here I loop and wait for the client choise
        BufferedReader in;
        String op;
        boolean exit = false;
        try {
            in = new BufferedReader(new InputStreamReader(incoming.getInputStream()));
            while ((op = in.readLine()) != null) {
            System.out.println("OP: " + op);
            if (op.equals("Elimina")) {
                String tmp = in.readLine();
                contenutoTextArea.append("Ho eliminato la mail ").append(tmp).append(" \n");
                textarea.setText(contenutoTextArea.toString());
                File file = new File("src/server/" + nomeAccount + "/" + tmp + ".txt");
                file.delete();
            }
        }
            System.out.println("bbbbb");
        } catch (IOException ex) {
            System.out.println("Unable to read messages");
        } finally {
            try {
                incoming.close();
            } catch (IOException ex) {
                System.out.println("Cannot close the socket");
            }
        }
    }
}

Answer 1

基於讀取您的客戶端代碼，看起來它已被阻止等待另一條消息，並且由於未到達流的末尾而未返回null。 一旦終止服務器進程，該過程就會繼續，這一事實證明了這一點。

如注釋中所述，您應確保關閉服務器端的PrintWriter 。 但是，這本身無法解決，因為流在​​套接字上，並且只要套接字仍處於打開狀態，就不會返回null。

您可以使用特定的控制字符串來回通信狀態（永遠不會是用戶輸入的東西，只是為了驗證通信是否已完成），然后檢查該行是否與控制字符串匹配，而不是檢查是否為空。 只需在兩側使用該技術即可來回傳遞控制，並確保完成后關閉插座。