Can't send object from Sever to Client

Question

Hi everyone, I'm a newby in this forum. I have a problem in Network programming. I'm creating a server and a client in my program for my homework. I used mysql.connector-java-5.0.7-bin.jar in my project.
Here is the problem; in my server class the necessary codes are
String username = inputFromClient.readUTF();
String password = inputFromClient.readUTF();
String sql = "SELECT * FROM user_information WHERE user_name = '"username"' AND password = '"password"'";
try {
stmt = connection.createStatement();
ResultSet rs =stmt.executeQuery(sql);
if(rs.next()){
outputToClient.writeUTF("Login succeeded");
System.out.println("Login succeeded");
String sql2 = "SELECT name from patient";
stmt = connection.createStatement();
objectToClient = new ObjectOutputStream(socket.getOutputStream());
ResultSet rs2 = stmt.executeQuery(sql2);
Vector v = new Vector();
while(rs.next()){
v.add(rs.getString(1));
objectToClient.writeObject(v);
else{
outputToClient.writeUTF("Login failed");
System.out.println("Login failed");
catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}and in my client class necessary codes are
try {
     Socket socket = new Socket("localhost", 8000);
     System.out.println("Connected to server");
     dataFromServer = new DataInputStream(socket.getInputStream());
     dataToServer =new DataOutputStream(socket.getOutputStream());
     dataToServer.writeUTF(username);
     dataToServer.writeUTF(password);
     String answ = dataFromServer.readUTF();
     if(answ.equals("Login succeeded")){
          try {
               try {
                    Vector v = (Vector)objectFromServer.readObject();
               } catch (ClassNotFoundException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
          } catch (IOException e1) {
               // TODO Auto-generated catch block
               e1.printStackTrace();
     else
     } catch (UnknownHostException e1) {
          // TODO Auto-generated catch block
          e1.printStackTrace();
     } catch (IOException e1) {
          // TODO Auto-generated catch block
          e1.printStackTrace();
     }After I start Server loging process works fine but then I get this exception
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
     at Client$4.actionPerformed(Client.java:298)
     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1879)
     at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2199)
     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:450)
     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:288)
     at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:264)
     at java.awt.Component.processMouseEvent(Component.java:5529)
     at javax.swing.JComponent.processMouseEvent(JComponent.java:3148)
     at java.awt.Component.processEvent(Component.java:5294)
     at java.awt.Container.processEvent(Container.java:2001)
     at java.awt.Component.dispatchEventImpl(Component.java:3996)
     at java.awt.Container.dispatchEventImpl(Container.java:2059)
     at java.awt.Component.dispatchEvent(Component.java:3844)
     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4249)
     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3929)
     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3859)
     at java.awt.Container.dispatchEventImpl(Container.java:2045)
     at java.awt.Window.dispatchEventImpl(Window.java:1810)
     at java.awt.Component.dispatchEvent(Component.java:3844)
     at java.awt.EventQueue.dispatchEvent(EventQueue.java:545)
     at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:268)
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:197)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:191)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:183)
     at java.awt.EventDispatchThread.run(EventDispatchThread.java:144)
And it points Vector v = (Vector)objectFromServer.readObject(); in Client class. It is a problem about sending Object but I can't figure it out. Maybe you can help? Thanks

Answer 1

Hi Aykt87,
In your server source, just have a look at this :
ResultSet rs2 = stmt.executeQuery(sql2);
Vector v = new Vector();
while(rs.next()){
v.add(rs.getString(1));
} rs2, rs?