使用ObjectInputStream而不是BufferedReader时获取BufferedReader

Question

我正在尝试建立一个连接到一个套接字服务器，它使用对象流进行读写。我能够将对象发送到服务器，但是当我尝试使用ObjectInputStream侦听响应时，我会得到一个错误。

注意： debug.debug()是围绕sout的包装器。

我的当事人：

public class Client {

    ObjectInputStream in;
    ObjectOutputStream out;

    Debug debug = new Debug();

    /**
     * Connect to a local socket server and start IO streams
     * @param port Port to connect to
     */
    public void connect(Integer port) {

        try{
            Socket socket = new Socket("localhost", port);
            debug.debug("CONNECTED", "GREEN");

            in = new ObjectInputStream(socket.getInputStream());
            out = new ObjectOutputStream(socket.getOutputStream());

            while (true) {
                try {
                    handleResponse(in.readObject());
                } catch (IOException e) {
                    debug.debug("CONNECTION_LOST", "ERROR");
                    break;
                }
            }
            connect(8080);
        } catch (Exception e) {
            debug.debug("Could not connect to host", "ERROR");
            try {
                Thread.sleep(3000);
                connect(8080);
            } catch (InterruptedException ex) {
                debug.debug("Sleep failed", "ERROR");
            }
        }
    }

    public void out(Model model) {

        try {
            out.reset();
            out.writeObject(model);
            debug.debug("Sent serialized object to server. [" + model.model + "]");
        } catch (IOException e) {
            debug.debug("Could not write object", "ERROR");
        }
    }

    private void handleResponse(Object model) {

        if (model instanceof User)
            if (((User)model).authorized)
//                ((User)model).dispatch();
                debug.debug("accepted");
    }

    public void main(String[] args) throws InterruptedException {

        connect(8080);
    }
}

登录类：

public final class Login extends JComponent implements Dispatcher {

    Button login;
    TextField email;
    PasswordField password;

    User User = new User();

    Debug debug = new Debug();

    public Login() {

        setLayout(new GridBagLayout());

        login = new Button("LOGIN", null);
        email = new TextField();
        password = new PasswordField();

        login.addActionListener(e -> {
            if (!email.getText().equals(""))
                if (!password.getText().equals("")) {
                    User.email = email.getText();
                    User.password = password.getText();
                    Admin.Socket.out(User);
                }
        });

        build();
    }

    public void userAuthorized() {

        debug.debug("authorized");
    }

    public void build() {

        GridBagConstraints constraint = new GridBagConstraints();

        constraint.anchor = GridBagConstraints.PAGE_START;
        constraint.gridx = 0;
        constraint.gridy = 0;
        constraint.gridheight = 1;
        constraint.gridwidth = 2;

        constraint.ipadx = 250;
        add(email, constraint);
        constraint.insets = new Insets(10, 0, 0, 0);
        constraint.gridy = 1;
        add(password, constraint);
        constraint.gridy = 2;
        constraint.ipadx = 100;
        constraint.ipady = 15;
        add(login, constraint);
    }
}

当我调用out方法时，这给了我一个java.lang.NullPointerException。但是，如果我使用BufferedReader来侦听，那么一切都会像预期的那样工作。

    public void connect(Integer port) {

        try{
            Socket socket = new Socket("localhost", port);
            debug.debug("CONNECTED", "GREEN");

            // BufferedReader instead of ObjectInputStream
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new ObjectOutputStream(socket.getOutputStream());

            while (true) {
                try {
//                    handleResponse(in.readObject());
                    debug.debug(in.readLine());
                } catch (IOException e) {
                    debug.debug("CONNECTION_LOST", "ERROR");
                    break;
                }
            }
            connect(8080);
        } catch (Exception e) {
            debug.debug("Could not connect to host", "ERROR");
            try {
                Thread.sleep(3000);
                connect(8080);
            } catch (InterruptedException ex) {
                debug.debug("Sleep failed", "ERROR");
            }
        }
    }

当我调用时，服务器接收发送的对象。但是，现在我无法侦听服务器返回的对象。我做错了什么？

编辑堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at socket.Client.out(Client.java:59)
    at applications.admin.components.Login.lambda$new$0(Login.java:48)
    at applications.admin.components.Login$$Lambda$6/500977346.actionPerformed(Unknown Source)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6527)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6292)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4883)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4705)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2739)
    at java.awt.Component.dispatchEvent(Component.java:4705)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
    at java.awt.EventQueue.access$400(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:697)
    at java.awt.EventQueue$3.run(EventQueue.java:691)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:719)
    at java.awt.EventQueue$4.run(EventQueue.java:717)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

编辑服务器：

public class Server {

    static Debug debug = new Debug();

    /**
     * Start a socket server
     */
    public void listen(Integer port, TextArea logs) {

        logs = logs != null ? logs : new TextArea();

        try {
            ServerSocket server = new ServerSocket(port);
            debug.debug("Server is running", "GREEN", logs);

            while (true) {
                Handler handler;
                try {
                    handler = new Handler(server.accept(), logs);
                    Thread client = new Thread(handler);
                    client.start();
                } catch (IOException e) {
                    debug.debug("CLIENT_ACCEPT Failed", "ERROR", logs);
                    System.exit(-1);
                }
            }

        } catch (IOException e) {
            debug.debug("SERVER_START Failed", "ERROR", logs);
        }
    }

    public void main(String[] args) throws InterruptedException {

        listen(8080, null);
    }
}

处理程序：

public class Handler implements Runnable {

    Socket client;
    Debug debug = new Debug();

    ObjectInputStream in;
    ObjectOutputStream out;

    TextArea logs;

    User user = new User();

    /**
     * Client instance running on new thread
     *
     * @param client Client Socket
     */
    Handler(Socket client, TextArea logs) {

        this.client = client;
        this.logs = logs;
        debug.debug("CLIENT_CONNECTED", "GREEN", logs);
    }

    /**
     * Listen to the client Stream and respond
     */
    @Override
    public void run() {

        try {
            in = new ObjectInputStream(client.getInputStream());
            out = new ObjectOutputStream(client.getOutputStream());

            while (true) {
                try {
                    try {
                        handleResponse((User) in.readObject());
                    } catch (ClassNotFoundException e) {
                        debug.debug("Unable to read object", "ERROR", logs);
                    }
                } catch (IOException e) {
                    debug.debug("CLIENT_DISCONNECTED", "ERROR", logs);
                    break;
                }
            }
        } catch (IOException e) {
            debug.debug("CONNECTION_FAILED", "ERROR", logs);
        }
    }

    private void handleResponse(User user) {

        debug.debug("Received serialized object from client. [" + user.model + "]", logs);

        if (user.auth()) {
            try {
                out.reset();
                out.writeObject(user);
                debug.debug("server: AUTHORIZED", "GREEN", logs);
            } catch (IOException e) {
                debug.debug("Couldn't write object", "ERROR", logs);
            }
        } else {
            debug.debug("server: UNAUTHORIZED", "ERROR", logs);
        }
    }
}

Answer 1

还不清楚Client和Login类是如何连接的，所以我来猜猜。

ObjectInputStream构造函数，如javadoc中所述，“将被阻塞，直到相应的ObjectOutputStream编写和刷新了标题”。因此，您的Client.connect()线程冻结在in = new ObjectInputStream(...)行，并且不为in和out设置值。(实际上，服务器线程也是出于同样的原因冻结的，所以您有一个死锁。)同时，Login线程试图向out写一些东西，但是out仍然是null，所以它得到了一个NullPointerException。

为什么BufferedReader不会发生这种情况呢？它不会阻塞构造函数，所以线程只是继续执行，为out设置非out值，每个人都很高兴。

修复:首先创建ObjectOutputStream并刷新它，这样另一端的ObjectInputStream就不需要等待了。换句话说，改变

in = new ObjectInputStream(socket.getInputStream());
out = new ObjectOutputStream(socket.getOutputStream());

至

out = new ObjectOutputStream(socket.getOutputStream());
out.flush();
in = new ObjectInputStream(socket.getInputStream());

在客户端和服务器上。

另一个问题是，Client.out字段不是volatile，而且没有明显的同步，所以即使在Client.connect()线程中out设置为非null值之后，Login线程也可能在那里看到null。因此，我建议您将Client.out字段设置为volatile (也可能是Client.in )。