为什么我使用 ObjectInputStream.readObject() 得到 ClassNotFoundException？

Question

以下客户端代码接受来自服务器的 "Guest" 对象：

protected static void sendLoginRequest(String email, String password) {
    try(
        Socket socket = new Socket("127.0.0.1", 44444);
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    ){
        out.write("LGNR");
        out.flush();
        out.newLine();
        out.flush();

        out.write(email);
        out.flush();
        out.newLine();
        out.flush();            

        out.write(password);
        out.flush();
        out.newLine();
        out.flush();

        in.ready();
        switch(in.readLine()) {
        case "SU":
            Guest g = null;
            try(ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());){
                g = (Guest) ois.readObject();
            }catch(ClassNotFoundException | IOException e) {
                System.out.println(e.getMessage());
                e.printStackTrace();
            }
            GuestProfileMenu.generateMenu(g);
            break;
        case "WP":
            System.out.println("Invalid Password.");
            break;
        case "IE":
            System.out.println("Email not found.");
            break;
        }

    }catch(IOException e) {
        System.out.println("No response from Server.");
        System.out.println(e.getMessage());
    }
}

在服务器端看起来像这样：

private void userLogin(Socket socket, BufferedReader in, BufferedWriter out) {
    System.out.println(socket.getInetAddress().getHostName() + ":" + socket.getLocalPort() + " - has sent a login request.\r\n");

    FileManager.openGuestFile();
    ArrayList<Guest> gList = FileManager.getGuestList();

    try{
        in.ready();
        String email = in.readLine();
        System.out.println(socket.getInetAddress().getHostName() + ":" + socket.getLocalPort() + " - Email received as: " + email);

        in.ready();
        String password = in.readLine();
        System.out.println(socket.getInetAddress().getHostName() + ":" + socket.getLocalPort() + " - Password received as: " + password);

        boolean exists = false;

        for(int i = 0; i < gList.size(); i++) {
            if (email.equals(gList.get(i).getEmail())) {
                exists = true;
                if (password.equals(gList.get(i).getPassword())) {                      
                    out.write("SU");
                    out.flush();
                    out.newLine();
                    out.flush();
                    try(ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());){            
                        oos.writeObject(gList.get(i));
                        oos.flush();
                    }catch(IOException e) {
                        System.out.println(e.getMessage());
                    }
                }else{
                    out.write("WP");
                    out.flush();
                    out.newLine();
                    out.flush();
                }
            }
        }
        if(!exists) {
            out.write("IE");
            out.flush();
            out.newLine();
            out.flush();
        }
        socket.close();
    }catch(IOException e) {
        System.out.println(e.getMessage());
    }

}

从客户端 returns ClassNotFoundException 在行 "g = (Guest) ois.readObject();":

java.lang.ClassNotFoundException: server.Guest
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at java.io.ObjectInputStream.resolveClass(Unknown Source)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)

错误消息说 "server.Guest" 的事实，即 (class package).(object)，我可以假设服务器的 Guest class 的实例不是与客户端的 Guest class 实例一样吗？那么如何通过套接字正确发送接收对象？

谢谢

Answer 1

The fact that the error message says "server.Guest", ie (class package).(object), can I assume that an instance of the server's Guest class isn't the same thing as an instance of the client's Guest class?

涉及到两个独立的 classes 是异常告诉你的，是的。

So how do I properly send a receive objects through a socket?

将自己限制在客户端和服务器都知道的 classes。有多种方法可以实现这一点，但它们几乎都涉及在连接的两端部署相同或等效的 .class 文件。 "Equivlent" 这里表示大约 "compiled from the same source with compilers of the same version".

为什么我使用 ObjectInputStream.readObject() 得到 ClassNotFoundException？

Why am I getting ClassNotFoundException with ObjectInputStream.readObject()?

java

serialization

classnotfoundexception

objectinputstream