Example of how to send an Object over a Socket in Java.

SendObjectsOverSockets.java

import java.io.Serializable;

// must implement Serializable in order to be sent
public class Message implements Serializable{
    private final String text;

    public Message(String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }
}

import java.io.*;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class Client {

    public static void main(String[] args) throws IOException {
        // need host and port, we want to connect to the ServerSocket at port 7777
        Socket socket = new Socket("localhost", 7777);
        System.out.println("Connected!");

        // get the output stream from the socket.
        OutputStream outputStream = socket.getOutputStream();
        // create an object output stream from the output stream so we can send an object through it
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);

        // make a bunch of messages to send.
        List<Message> messages = new ArrayList<>();
        messages.add(new Message("Hello from the other side!"));
        messages.add(new Message("How are you doing?"));
        messages.add(new Message("What time is it?"));
        messages.add(new Message("Hi hi hi hi."));

        System.out.println("Sending messages to the ServerSocket");
        objectOutputStream.writeObject(messages);

        System.out.println("Closing socket and terminating program.");
        socket.close();
    }
}


import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.List;

public class Server {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        // don't need to specify a hostname, it will be the current machine
        ServerSocket ss = new ServerSocket(7777);
        System.out.println("ServerSocket awaiting connections...");
        Socket socket = ss.accept(); // blocking call, this will wait until a connection is attempted on this port.
        System.out.println("Connection from " + socket + "!");

        // get the input stream from the connected socket
        InputStream inputStream = socket.getInputStream();
        // create a DataInputStream so we can read data from it.
        ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);

        // read the list of messages from the socket
        List<Message> listOfMessages = (List<Message>) objectInputStream.readObject();
        System.out.println("Received [" + listOfMessages.size() + "] messages from: " + socket);
        // print out the text of every message
        System.out.println("All messages:");
        listOfMessages.forEach((msg)-> System.out.println(msg.getText()));

        System.out.println("Closing sockets.");
        ss.close();
        socket.close();
    }
}

// Server output
/*
ServerSocket awaiting connections...
Connection from Socket[addr=/127.0.0.1,port=62360,localport=7777]!
Received [4] messages from: Socket[addr=/127.0.0.1,port=62360,localport=7777]
All messages:
Hello from the other side!
How are you doing?
What time is it?
Hi hi hi hi.
Closing sockets.
*/

// Client output
/*
Connected!
Sending messages to the ServerSocket
Closing socket and terminating program.
*/