NullPointerException 套接字 - Android？

Question

我正在尝试使用 LINK。

这是客户端代码：

public class MainActivity extends AppCompatActivity {

    private Socket socket;

    private static final int SERVERPORT = 5001;
    private static final String SERVER_IP = "127.0.0.1";
    Button myButton;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myButton = (Button)findViewById(R.id.myButton);
        myButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    EditText et = (EditText) findViewById(R.id.EditText01);
                    String str = et.getText().toString();

                    PrintWriter out = new PrintWriter(new BufferedWriter(
                            new OutputStreamWriter(socket.getOutputStream())),
                            true);
                    out.println(str);
                } catch (UnknownHostException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
        new Thread(new ClientThread()).start();
    }

    class ClientThread implements Runnable {

        @Override
        public void run() {

            try {
                InetAddress serverAddr = InetAddress.getByName(SERVER_IP);

                socket = new Socket(serverAddr, SERVERPORT);

            } catch (UnknownHostException e1) {
                e1.printStackTrace();
            } catch (IOException e1) {
                e1.printStackTrace();
            }

        }

    }
}

这里是服务器代码：

   public class MainActivity extends AppCompatActivity {

    private ServerSocket serverSocket;

    Handler updateConversationHandler;

    Thread serverThread = null;

    private TextView text;

    public static final int SERVERPORT = 6001;

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        text = (TextView) findViewById(R.id.text2);

        updateConversationHandler = new Handler();

        this.serverThread = new Thread(new ServerThread());
        this.serverThread.start();

    }

    @Override
    protected void onStop() {
        super.onStop();
        try {
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    class ServerThread implements Runnable {

        public void run() {
            Socket socket = null;
            try {
                serverSocket = new ServerSocket(SERVERPORT);
            } catch (IOException e) {
                e.printStackTrace();
            }
            while (!Thread.currentThread().isInterrupted()) {

                try {

                    socket = serverSocket.accept();

                    CommunicationThread commThread = new CommunicationThread(socket);
                    new Thread(commThread).start();

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    class CommunicationThread implements Runnable {

        private Socket clientSocket;

        private BufferedReader input;

        public CommunicationThread(Socket clientSocket) {

            this.clientSocket = clientSocket;

            try {

                this.input = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));

            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        public void run() {

            while (!Thread.currentThread().isInterrupted()) {

                try {

                    String read = input.readLine();

                    updateConversationHandler.post(new updateUIThread(read));

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    class updateUIThread implements Runnable {
        private String msg;

        public updateUIThread(String str) {
            this.msg = str;
        }

        @Override
        public void run() {
            text.setText(text.getText().toString()+"Client Says: "+ msg + "\n");
        }
    }
}

收到以下错误消息，我在服务器上看不到任何消息：

Answer 1

在您的客户端代码中，您还没有创建客户端套接字，但是，您正在尝试使用 socket.getOutputStream() 获取该套接字的输出流。由于 socket 为 null，因此，您的代码抛出 NullPointerException。

因此，为客户端创建一个套接字对象以连接到服务器，如下所示：

public class MainActivity extends AppCompatActivity {

private Socket socket;

private static final int SERVERPORT = 5001;
private static final String SERVER_IP = "127.0.0.1";
Button myButton;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    myButton = (Button)findViewById(R.id.myButton);
    myButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try {
                EditText et = (EditText) findViewById(R.id.EditText01);
                String str = et.getText().toString();
//create socket object as shown below before retrieving the OutputStream object.
                socket = new Socket(MainActivity.SERVER_IP,MainActivity.SERVERPORT);
                PrintWriter out = new PrintWriter(new BufferedWriter(
                        new OutputStreamWriter(socket.getOutputStream())),
                        true);
                out.println(str);
            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
    new Thread(new ClientThread()).start();
}
//.... and your code goes on!

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