How I can send a object from Client to Server in Java?

Question

Hi i want test a connection between Client and Server in Java. For Example I want to send a object from client to Server. The object is a User that I built.

If I start the Server and the Client I get this error:

  run:
java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:209)
    at java.net.SocketInputStream.read(SocketInputStream.java:141)
    at java.net.SocketInputStream.read(SocketInputStream.java:223)
    at java.io.ObjectInputStream$PeekInputStream.peek(ObjectInputStream.java:2296)
    at java.io.ObjectInputStream$BlockDataInputStream.peek(ObjectInputStream.java:2589)
    at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2599)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1319)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at taraticketclienttest.TaraTicketClientTest.main(TaraTicketClientTest.java:37)
BUILD SUCCESSFUL (total time: 0 seconds)

Here is my Client:

public static void main(String[] args) throws ClassNotFoundException {

        try(Socket socket = new Socket("localhost", 7778)) {

            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
            ObjectInputStream in = new ObjectInputStream(socket.getInputStream());

            User u = new User("Wowa");

            out.writeObject(u);

            User u2 = (User)in.readObject();

            System.out.println(u2.getName());


        } catch (IOException ex) {
          ex.printStackTrace();
        }
    }

Here is my Server:

public class DemoServer {
public static void main(String[] args) throws ClassNotFoundException {
    try(ServerSocket serverSocket = new ServerSocket(7778)) {

        while (true) {                
            Socket clientSocket = serverSocket.accept();
            System.out.println("socket open...");

            ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream());
            ObjectOutputStream out = new ObjectOutputStream(clientSocket.getOutputStream());

            User u = (User) in.readObject();

            System.out.println(u.getName());

            out.writeObject(u);
        }

    } catch (IOException ex) {
      ex.printStackTrace();
    }
}

}

Here is my User:

public class User implements Serializable {
private String name; 

public User(){}

public User(String name){
    this.name = name;
}

public String getName(){
    return this.name;
}

}

Answer 1

You need your class User to implement Serializable:

public class User implements Serializable {
    ...
}

Objects can not be writen to / read from ObjectInputStream or ObjectOutputStream unless they implement Serializable

Answer 2

As an alternative you could send the object as a String in JSON format, by using Jackson or Boon. They are definitely faster than defalut java object serialization (and you don't need to make the class Serializable)

You can get more info on JSON-Object serialization using jackson in the following link how-to-convert-java-object-to-from-json-jackson