Socket implementation with ObjectInputStream - can't read object - sockets

Question

For a Java class I am taking, I need to use sockets to pass data back and forth between client and server. While I can get examples to work passing string data, I need to be able to pass custom class objects (i.e. a product) and lists of these objects back and forth. I cannot get the server piece to successfully read the input. I tried to create a simple example of my code to see if anyone can pinpoint the issue. I do understand that I don't have the code complete, but I cannot even get the server to read the object the the class is writing to the stream (in this case, I am writing a string just in an attempt to get it to work, but need to read/write objects). Here is my code. I have spent hours and hours trying this and researching other people's questions and answere, but still can't get this to work.
Here the sample code:
simple server:
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class simpleServer {
public static final int PORT_NO = 8888;
static ObjectInputStream serverReader = null;
public static void main(String[] args) throws IOException, InterruptedException {
ServerSocket serverSocket = new ServerSocket(PORT_NO);
System.out.println("... server is accepting request");
Object myObject = null;
while (true) {
Socket socket = serverSocket.accept();
System.out.println("creating reader");
ObjectOutputStream objOut = new ObjectOutputStream(socket.getOutputStream());
serverReader = new ObjectInputStream(socket.getInputStream());
System.out.println("created reader");
try {
System.out.println("try to read");
myObject = serverReader.readObject();
System.out.println("read it");
System.out.println(myObject);
if (myObject != null) objOut.writeUTF("Got something");
else objOut.writeUTF("got nothing");
if ("quit".equals(myObject.toString())) serverSocket.close();
} catch (ClassNotFoundException e1) {
// TODO Auto-generated catch block
System.out.println("cath for readobject");
}
catch (Exception e) {
System.out.println("other error");
System.out.println(e.getMessage());
}
}
}
}
simple client:
public static void main(String[] args) {
Socket socket;
try {
socket = new Socket("localhost", ProductDBServer.PORT_NO);
ObjectOutputStream objOut = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream objIn = new ObjectInputStream(socket.getInputStream());
objOut.writeUTF("loadProductsFromDisk");
objOut.flush();
String myString = objIn.toString();
//System.out.println(myString);
if (!"quit".equals(objIn.toString().trim())) {
//System.out.println("reading line 1");
String line;
try {
line = (String)objIn.readObject();
//System.out.println("line is " + line);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
objIn.close();
//System.out.println("result: " + line);
}
System.out.println("closing socket");
socket.close();
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
System.out.println("Unknownhostexception");
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
System.out.println("ioexception");
e.printStackTrace();
}
}
The code appears to run to the point on the server side where it trys to read the object I sent, and then dies. Can someone see what I am doing wrong? This seems to be such a simple thing to do, and yet I can't seem to get it to work. Thanks for any help!

Answer 1

To write objects to an ObjectOutputStream you need to call writeObject().
Not writeUTF().
To read objects from an ObjectInputStream you need to call readObject().
Not toString().

Answer 2

See in your code:
// Simple Client
objOut.writeUTF("loadProductsFromDisk"); // Line 8
You are sending the String "loadProductsFromDisk" in the UTF-8 format towards the server side.
So in order to receive it and read it over the server side, you will need something like this:
String clientReq = serverReader.readUTF();
Where, serverReader is your ObjectInputStream object.
Otherwise, if you wish to send and receive objects you must use the
writeObject() & readObject() methods respectively.