Android/Java - ClassNotFoundException for ServerSocket and Socket communication

Question

I'm developing an app where the phone (Android program) is the client trying to send data through a socket to a Java receiver program on my computer.

So far I've been able to send simple strings or whatever, but now I'm trying to send custom objects that I create. I should note that both programs are separate Eclipse projects, and I seem to be having trouble including the same custom class "Order" on the server side (even though I have Order.java in the src folder of the server project).

Some code, for reference: Server:

private void run() throws Exception {

    ServerSocket mySS = new ServerSocket(4443);     

    while(true) {

        Socket SS_accept = mySS.accept(); 

        InputStream is = SS_accept.getInputStream();  
        ObjectInputStream ois = new ObjectInputStream(is);  
        Order order = (Order) ois.readObject();  

        if (order!=null){
            java.util.List<String> items = order.getOrders(); 
            int chair = order.getChair();
            int table = order.getTable(); 
            double price = order.getPrice(); 
            System.out.println("Table: "+ table + " || Chair: " +chair);
            for(String food: items) {
                System.out.println(food); 
            }
            System.out.println("Price: $"+price); 

        }  
        is.close();  
        SS_accept.close();  
        mySS.close();

}

And the relevant part of the client:

try {
        mySocket = new Socket(serverService.ipAddress, serverService.port);
        os = mySocket.getOutputStream();  
        oos = new ObjectOutputStream(os);  
    } catch(Exception e) {
        Toast.makeText(PlaceOrder.this, "Error - not connected to server.", Toast.LENGTH_SHORT).show(); 
    }

try {
                oos.writeObject(order);
                Toast.makeText(PlaceOrder.this, "Order Submitted!", Toast.LENGTH_SHORT).show(); 
                refreshOrderPage(); //refresh page, allow waiter to make more orders
                oos.close();  
                os.close(); 
                mySocket.close(); 
            } catch (Exception e) {
                Toast.makeText(PlaceOrder.this, "Error - not connected to server.", Toast.LENGTH_SHORT).show();
            }

Any ideas why I'm getting this error when trying to send objects through sockets?

Thanks.

Femi · Accepted Answer · 2011-08-25 03:22:24Z

2

You should probably set the serialVersionUID in the class, then build a jar with the shared classes and include that jar in both projects.

However, given you are using different JVMs (Oracle and Dalvik) there's no guarantee that the byte-level encoding is the same. You should either manually override the serialization using readObject/writeObject or use a different object encoding system that is guaranteed to be identical independent of the environment.

answered Aug 25, 2011 at 3:22

Femi

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Comments

Ryan Stewart · Accepted Answer · 2011-08-25 03:14:00Z

0

A stack trace would help, but almost certainly you're serializing an object on one side, sending it to the other, and the other side doesn't have a class definition with which it can reconstruct the object. In this case, it sounds like maybe your Server doesn't know about the com.foo.Order class.

answered Aug 25, 2011 at 3:14

Ryan Stewart

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2 Comments

JDS Over a year ago

hi. It's weird, I don't know how else to include the file. I literally copy and pasted the code into a file called "Order.java" in the Server's project...

Ryan Stewart Over a year ago

Is it in the same package on both the server and the client? Does the class get compiled and deployed/run along with all the other server classes?

Mikita Belahlazau · Accepted Answer · 2011-08-25 03:18:16Z

0

You can also serialize object to some string format (json, yaml, xml) and pass it. It would much easier to maintain, I suppose.

answered Aug 25, 2011 at 3:18

Mikita Belahlazau

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