Serialization and Deserialization through message queue

Question

I have an Employee class as below:

package com.mypackage.rabbitmq.model
import java.io.Serializable;

import javax.xml.bind.annotation.XmlRootElement;


@XmlRootElement
public class Employee implements Serializable{

    /**
    * 
    */
    private static final long serialVersionUID = -2736911235490297622L;
    private int EmpNo;
    private String FirstName;
    private String LastName;
    private int age;
    private String gender;
    private String skill;
    private long phone;
    private String email;
    private double salary;
    //getters and setters

I published the list of employee in rabbit MQ as below:

package com.mypackage.rabbitmq.client.publisher;

//imports

public class Publisher {

    public static void main(String[] args) throws IOException {
        ConnectionFactory factory = new ConnectionFactory();

        Connection con = factory.newConnection("localhost");
        Channel channel = con.createChannel();

        Gson gson  = new GsonBuilder().create();
        Employee employee = null;

        List<Employee> empList = new ArrayList<>();
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);

        String queueName = "TestQueue";
        for(int i=1; i<=10; i++){
            employee = newEmp(i);

            String message =gson.toJson(employee);
            System.out.println("queueName: "+queueName);
            empList.add(employee);

        }
        oos.writeObject(empList);
        channel.basicPublish(1, "", queueName, null, bos.toByteArray());
        System.out.println("[X], sent '"+empList+"'");

        channel.close(0, queueName);
        con.close(0, queueName);
    }

    public static Employee newEmp(int i){

        //logic here
    }
}

From a separate spring boot application I tried to consume the list of employee. In the consumer application I have the same employee class structure. However the package is different.

package org.springboot.consumer.model;

import java.io.Serializable;

public class Employee implements Serializable{
    //fields and getters-setters here
}

In brief consumer code is as bellow:

public class SDPRabbitMQConsumer implements MessageListener {

    @Override
    public void onMessage(Message message) {
        Gson gson  = new GsonBuilder().create();
        try {
            ByteArrayOutputStream os = new ByteArrayOutputStream();
            os.write(message.getBody(), 0, message.getBody().length);
            ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
            ObjectInputStream objInputStream = new ObjectInputStream(is);
            System.out.println("objInputStream.readObject().toString()"+objInputStream.readObject().toString());
            Employee[] employeeArray = gson.fromJson(objInputStream.readObject().toString(), Employee[].class);
            List<Employee> employeeList = new ArrayList<Employee>(Arrays.asList(employeeArray));
            for(Employee employee: employeeList){
                System.out.println(employee);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

But I am getting the below exception:

java.lang.ClassNotFoundException: com.mypackage.rabbitmq.model.Employee

It seems it's a Serialization and Deserialization issue.

My questions are:

1. If I publish Employee instead of List I don't even need to serialize the class. Then why I need to serialize in case of List?
2. Why this Exception? Do we need to maintain same package structure for a serialized class in both end?
3. In the consumer side do we need to have serialVersionUID? If yes, should it match with that of publisher's side?

Thanks in advance.

Answer 1

1) while java.util.List is not Serializable, all standard implementations are, so you should be able to serialize/deserialize an ArrayList for instance.

2) Yes, you need the same class in the same package, and also..

3) Classes in both ends must have the same serialVersionUID