El objeto serializado tiene valores nulos después de enviarse a través de udp

I have set up a UDP client/server model that can send string messages to each other.

I've created a custom class LoginRequest which is serialized and sent to the server containing the username and password. When the getters for these variables are called they return null values even though I check the variables before the LoginRequest is sent.

Here is the code for serializing and sending datagram from the client:

private void login(String name, char[] pass) throws SQLException {
    try {
        LoginRequest login = new LoginRequest(name, pass);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        byte[] buffer= baos.toByteArray();
        DatagramPacket packet =
                new DatagramPacket(buffer, buffer.length, InetAddress.getByName(SERVER), 10110);
        DatagramSocket sSocket = new DatagramSocket();

    } catch (Exception e) {

Here is the code for de-serializing the LoginRequest and reading the username:

private void readMessage() {
    try {
            ByteArrayInputStream bais = new ByteArrayInputStream(cPacket.getData());
            ObjectInputStream ois = new ObjectInputStream(bais);
            Object obj = ois.readObject();
            if(obj instanceof LoginRequest) {
                System.out.println("Login request");
                LoginRequest login = (LoginRequest) obj;
            } else {
                System.out.println("Not a login request");
        } catch (Exception e) {

Here is the Code for the LoginRequest:

public class LoginRequest implements Serializable {
private static final long serialVersionUID = -1379800611469143228L;
private static String username;
private static char[] password;

public LoginRequest(String name, char[] pass) {
    username = name;
    password = pass;

public String getUsername() {
    System.out.println("Username: " + username);
    return username;

public char[] getPassword() {
    String p = password.toString();
    System.out.println("Password: " + p);
    return password;

When I attempt to read the username or password after this deserialization, I get a NullPointerException. I will be extremely happy if someone can point me in the right direction.

preguntado el 09 de marzo de 12 a las 23:03

Could you put the code of LoginRequest? And where does your NPE occurs, I can't find it in your code. Finally, but this is the obvious, did you check that the name and password are not empty on the sending side? -

username and password are null on server side but give the correct values on the client side, I get the NPE when I call getPassword(). getUsername() returns a null value. -

2 Respuestas

Suelta el static on your attribute usename and password!

respondido 09 mar '12, 23:03

You are welcome, but you should probably learn what static means because it made absolutely no sense to use it in your case. - Guillermo Polet

Instead of reading your LoginRequst as a generic object, you can do it this way:

LoginRequest loginRequest = (LoginRequest)ois.readObject();

You can also override the readObject() method in your LoginRequest class. Because the readObject method is responsible for reading and restoring the state of the object for a particular class that you serialized. I am giving you a direction to think.

respondido 09 mar '12, 23:03

To the risk of having a ClassCastException. - Guillermo Polet

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