确保服务器端的消息是 rusl .online.examination.system.client.utility.Message 。似乎并非如此。

I have 2 java netbeans projects, one is the Server other is the Client. I have a Message class that I have created which I want to pass to the server and back the other way to the client after modification done at the server. I have included the class Message in both projects. I use ObjectOutputStream and ObjectInputStream to pass the object. The connection between the server and the client is ok and the object passes through but at the server when I read the object from the ObjectInputStream using readObject() method I type cast it to the Message class. But an ClassNotFoundException is thrown at the server. It cant find the Message class. How can I resolve this?

Code for the client:

public void startClient() {
    try {
        // Create the socket
        Socket clientSocket = new Socket(HOST, PORT);
        // Create the input & output streams to the server
        ObjectOutputStream outToServer = new ObjectOutputStream(clientSocket.getOutputStream());
        ObjectInputStream inFromServer = new ObjectInputStream(clientSocket.getInputStream());

        // Read modify
        // TODO here

        /* Create The Message Object to send */
        LinkedList<Message> msgList = new LinkedList<>();
        Message msg = new Message();
        msg.setMessage("Kasun");
        msg.setIndex(1);
        msg.setAverage(5.5f);
        msgList.push(msg);

        /* Send the Message Object to the server */
        outToServer.writeObject(msgList);            

        /* Retrive the Message Object from server */
        LinkedList<Message> inFromServerList = new LinkedList<>();
        Message msgFrmServer = null;
        inFromServerList = (LinkedList<Message>)inFromServer.readObject();
        msgFrmServer = inFromServerList.pop();

        /* Print out the recived Message */
        System.out.println("Message: " + msgFrmServer.getMessage());
        System.out.println("Index: " + msgFrmServer.getIndex());
        System.out.println("Average: " + msgFrmServer.getAverage());


        clientSocket.close();

    } catch (Exception e) {
        System.err.println("Client Error: " + e.getMessage());
        System.err.println("Localized: " + e.getLocalizedMessage());
        System.err.println("Stack Trace: " + e.getStackTrace());
    }
}

Code for the Server

public void startServer() {

    try {
        ServerSocket welcomeSocket = new ServerSocket(PORT);

        while (true) {    
            // Create the Client Socket
            Socket clientSocket = welcomeSocket.accept();
            System.out.println("Socket Extablished...");
            // Create input and output streams to client
            ObjectOutputStream outToClient = new ObjectOutputStream(clientSocket.getOutputStream());
            ObjectInputStream inFromClient = new ObjectInputStream(clientSocket.getInputStream());

            // Read modify
            // TODO here

            /* Create Message object and retrive information */
            LinkedList<Message> inList = new LinkedList<>();
            Message inMsg = null;
            inList = (LinkedList<Message>)inFromClient.readObject();
            inMsg = inList.pop();

            /* Modify the message object */
            inMsg.setMessage(inMsg.getMessage().toUpperCase());
            inMsg.setIndex(5);
            inMsg.setAverage(10.5f);

            /* Send the modified Message object back */
            outToClient.writeObject(inMsg);        

        }

    } catch (Exception e) {
        System.err.println("Server Error: " + e.getMessage());
        System.err.println("Localized: " + e.getLocalizedMessage());
        System.err.println("Stack Trace: " + e.getStackTrace());
        System.err.println("To String: " + e.toString());
    }
}

The exception thrown at the "server"

java.lang.ClassNotFoundException: rusl.online.examination.system.client.utility.Message

Would I have to use java RMI? Is there a solution for this without using RMI?

Make sure that Message on server side is rusl.online.examination.system.client.utility.Message. It seems not to be the case.