DataOutputStream 第二次不工作

问题描述

我想向服务器写一条消息。我第一次发送消息时一切正常。但是第二次我想发送另一个命令时，dos.writeUTF(message); 行抛出了 NullPointerException。我真的不知道为什么。

GUICLIENT_INSTANCE 用于我的 Swing 课程

这是我的初始化方法：

private void initialize() {
        if (name != null && ip != null && port != 0) {
            String verify = "/v/" + name + "/" + ip + "/" + port + "/e/";
            boolean connect = openConnection(ip,port);
            if (connect) {
                send(verify);

                String receiveMsg = "";
                String[] temp = {};

                try {
                    try {
                        if (dis.available() > 0) {
                            receiveMsg = dis.readUTF();
                        }

                    } catch (Exception e2) {
                        e2.printstacktrace();
                    }

                    System.out.println(receiveMsg);
                    temp = splitMsg(receiveMsg,"/");

                    if (receiveMsg.startsWith("/er/")) {
                        if (temp[2].equals("disconnected")) {
                            s.close();
                            GUICLIENT_INSTANCE.connectFail();
                        }

                    } else {
                        System.out.println("Showing connected");
                        try {
                            System.out.println("Connected!");
                            GUICLIENT_INSTANCE.connected();
                        } catch (InterruptedException e) {
                            e.printstacktrace();
                        }
                    }
                } catch (Exception e1) {
                    GUICLIENT_INSTANCE.connectFail();
                }

                System.out.println(receiveMsg);

            } else {
                System.err.println("No server found with Address: " + ip + ":" + port);
                GUICLIENT_INSTANCE.connectFail();
            }
        }

    }

我打开我的连接：

private boolean openConnection(String Sip,int port) {
        try {
            InetAddress ip = InetAddress.getByName(Sip);
            s = new Socket(ip,port);
            dis = new DataInputStream(s.getInputStream());
            dos = new DataOutputStream(s.getoutputStream());

        } catch (Exception e) {
            return false;
        }

        return true;
    }

这是我发送方法的代码：

public void send(String message) {
        try {
            if (s.isConnected()) {
                
                dos.writeUTF(message);

            } else {
                System.err.println("Failed sending! No connection!");
            }

        } catch (Exception e) {
            e.printstacktrace();
        }

    }

解决方法

试试

public void send(String message) {
    if (message == null) {
        throw new IllegalArgumentException("null message not allowed");
    }
    if (dos == null) {
        throw new IllegalStateException("output stream is null");  
        // or new IOException
    }
    ...