Receiving user defined Object over TCP with ClassNotFoundException

Question

I'm developing a client/server application that uses TCP connection. I need to send a user defined object from server to client. everything is working fine until the client receives the object, it throws the ClassNotFoundException even though the class is on both sides and I cast it, and it is Serializable.

The exception at client side is:

     Exception in thread "main" java.lang.ClassNotFoundException: jggserver.Question

I don't know why the client is casting using the server package. (they are different projects).

here is the code at client side, where the exception is:

    q = (Question) clientInputStream.readObject();

code at server side:

    serverOutputStream.writeObject(question);

Although I went through several tutorials and they do the exact thing.

I appreciate any help.

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COMMENTS:

user1697575, both programs are on the same computer and same IDE (netbeans).

• I don't know about the TCP payload, I will search about it.

• I create the class on the server then refactor it on the client, I don't know if it's the correct way or not.

• I can't use RMI because I'm asked to specifically use this way to implement my project.

many thanks.

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SOLVED: I created a separate package and added Question class to it, then I included this package in the server and the client programs.

thank you all guys, specially Juan.

Answer 1

I think the answer is in your question, here "I don't know why the client is casting using the server package. (they are different projects)." .

If packages on server and client are different, is impossible that standard serialisation system works.

You need create a class that is present is both projects with same name and package, really "same code".

Answer 2

There are many check points to consider:

• JVM version on client and server
• TCP bytes payload check to see if they aren't get corrupted/translated
• Class versions loaded on the client and server

Also out of curiosity, why don't you use a robust RMI standard framework that taking care of many things for you?

Answer 3

The class is not present on both sides. That's what the exception is telling you. It has to be the same class name, in the same package.