sending objects to/from client/server

Question

I'm on the search for a solution to my error which occur while trying to send an object from server side to client side.

The object in form as a class instance will be created by clicking on a JButton. A client class will also be created which transfer the object to the server. No errors will occur. But when it comes to send a new object back to the client a ClassCastException will be thrown.

ActionListener Class

class ActionHandler implements ActionListener {
   String buttonPressed;
   List<String> parameterList = new ArrayList<String>();

   public void actionPerformed(ActionEvent event) {
      if(event.getSource() == executeNameSearch) {
         buttonPressed = "NameSearch";
         parameterList = new ArrayList<String>();
         parameterList.add(pizzaNameSearch.getText());
         ObjectToServer object = new ObjectToServer(buttonPressed, parameterList);

         // build connection to server
         Client client = new Client();
         client.connectToServer(object);
      }
      else if(event.getSource() == executeNameSearch) {
         buttonPressed = "IDSuche";
         parameterList = new ArrayList<String>();
         parameterList.add(pizzaIDSearch.getText());
         ObjectToServer object = new ObjectToServer(buttonPressed, parameterList);

         Client client = new Client();
         client.connectToServer(object);
      }
      // some more actionPerformed cases..
   }
}

Client class

public class Client {
   public void connectToServer(ObjectToServer object) {
      Socket server = null;
      try {
         server = new Socket("localhost", 3141);
         ObjectOutputStream oos = new ObjectOutputStream(server.getOutputStream());
         ObjectInputStream ois = new ObjectInputStream(server.getInputStream());

         // sending object to server
         oos.writeObject(object);
         oos.flush();

         // receiving object from server
         try {
            // ERROR BY TRYING TO CAST HERE
            ObjectToClient objectIn = (ObjectToClient) ois.readObject();
         } catch (ClassNotFoundException e) {
            e.printStackTrace();
         }

         oos.close();
         ois.close();
      } catch(UnknownHostException e) {
         e.printStackTrace();
      } catch(IOException e) {
         e.printStackTrace();
      } finally {
         if(server!=null) {
            try {
               server.close();
            } catch(IOException e) {
               System.out.println(e);
            }
         }
      }
   }
}

Server Class

public class Server {
   static PizzaManager manager = new PizzaManager();
   private static void handleConnection(Socket client) throws IOException {
      ObjectInputStream ois = new ObjectInputStream(client.getInputStream());
      ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream());

      ObjectToServer objectIn;
         try {
            objectIn = (ObjectToServer) ois.readObject();
            String buttonPressed = objectIn.getButtonPressed();

            if(buttonPressed.equals("NamenSuche")) {
               String searchedPizzaName = objectIn.getParameterList().get(0);
               manager.namenSuche(searchedPizzaName);

               ObjectToClient objectOut = new ObjectToClient();
               objectOut.setResults(manager.getResults());
               oos.writeObject(objectIn);
            }
            // some more cases..
         } catch (ClassNotFoundException e) {
            e.printStackTrace();
         }

         ois.close();
         oos.close();
   }

   public static void main(String[] args) throws IOException {
      ServerSocket server = new ServerSocket(3141);
      while(true) {
         Socket client = null;
         try {
            client = server.accept();
            handleConnection(client);
         }
         catch(IOException e) {
            e.printStackTrace();
         }
         finally {
            if(client!=null) {
                try {
                    client.close();
                }
                catch(IOException e) {
                }
            }
        }
      }
   }
}

StackTrace

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: 
transfer.ObjectToServer cannot be cast to server.ObjectToClient
at client.Client.connectToServer(Client.java:34)
at gui.Pizzasuche$ActionHandler.actionPerformed(Pizzasuche.java:362)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Thank you for your help!

Answer 1

I think that in your Server class, you're trying to send back the wrong object. Shouldn't it be :

oos.writeObject(objectOut);

?

Right now you are sending back objectIn which is an ObjectToServer instance (or at least casted as so) whereas you're trying to cast it as an ObjectToClient client-side hence the ClassCastException.

Fixed Server class :

public class Server {
   static PizzaManager manager = new PizzaManager();
   private static void handleConnection(Socket client) throws IOException {
      ObjectInputStream ois = new ObjectInputStream(client.getInputStream());
      ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream());

      ObjectToServer objectIn;
         try {
            objectIn = (ObjectToServer) ois.readObject();
            String buttonPressed = objectIn.getButtonPressed();

            if(buttonPressed.equals("NamenSuche")) {
               String searchedPizzaName = objectIn.getParameterList().get(0);
               manager.namenSuche(searchedPizzaName);

               ObjectToClient objectOut = new ObjectToClient();
               objectOut.setResults(manager.getResults());
               oos.writeObject(objectOut); // instead of objectIn
            }
            // some more cases..
         } catch (ClassNotFoundException e) {
            e.printStackTrace();
         }

         ois.close();
         oos.close();
   }

   public static void main(String[] args) throws IOException {
      ServerSocket server = new ServerSocket(3141);
      while(true) {
         Socket client = null;
         try {
            client = server.accept();
            handleConnection(client);
         }
         catch(IOException e) {
            e.printStackTrace();
         }
         finally {
            if(client!=null) {
                try {
                    client.close();
                }
                catch(IOException e) {
                }
            }
        }
      }
   }
}