RMI partially working

Question

Alright guys, I am currently trying to run an application that reads the details of a Book from a remote server. The RMIRegistry is running fine, the Server runs no problems and to a certain extent the application is working. See below:
C:\libsysRMI>java LibraryApplication
ISBN=0-x2-783637898-S
Title=Java RMI
Exception occurred while creating myBook: java.rmi.UnmarshalException: error unmarshalling return; nested exception is:
java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: CopyImpl
However I am getting an error as can be seen, this should be returning the copies of the book. The problem seems to be with my copyImpl class which is included below along with the Application class where the exception is being thrown.
import java.util.Collection;
public class CopyImpl implements CopyIF{
  private BookIF book;
  private Collection loans;
  private String copyNo;
  public CopyImpl(String copyNo) {
    this.copyNo = copyNo;
  public String getCopyNo(){
    return copyNo;
  public java.util.Collection getLoans(){
    return loans;
  public BookIF getBook(){
    return book;
  public String toString(){
    return "[copy="+copyNo+  "]" ;
import java.util.*;
import java.rmi.*;
public class LibraryApplication {
  public static final String serverName="localhost";
  public LibraryApplication() {
    BookIF book = getRemoteBook();
    try{
       //call the remote method getISBN...
       print("ISBN="+book.getISBN());
       //call the remote method getTitle...
       print("Title="+book.getTitle());
       //call the remote method getCopies...
       print("Number of copies="+book.getCopies().size());
       //another call to the remote method getCopies... for the same data
       printCopies(book.getCopies());
        * Replace with transfer object pattern, should allow 1 call instead of 4 I think
    }catch(RemoteException ex){
      System.out.println("Exception occurred while creating myBook: " + ex);
  private BookIF getRemoteBook() {
    Collection authors=null;
    BookIF myBook = null;
    try{
      //instead of local call, bind to the remote instance
      //myBook = new BookImpl("Java is Good","0-xug68904847", authors, null);
      myBook = (BookIF) Naming.lookup("//"+serverName+"/myBook_one");
      //Collection copies = getCopies(myBook);
      //myBook.setCopies(copies);
    }catch(Exception ex){
      System.out.println("Exception occurred while creating myBook: " + ex);
    return myBook;
  private void print(Object o){
    System.out.println(o.toString());
  private void printCopies(Collection copies){
    if(copies !=null){
      System.out.println(copies.toString());
    }else{
      System.out.println("no copies found.");
  private Collection getCopies(BookIF book){
    Collection copies = new Vector();
    for(int i=0;i<10;i++){
      copies.add(new CopyImpl("my copy "+i));
    return copies;
  public static void main(String[] args){
    LibraryApplication library = new LibraryApplication();
}Any ideas what could be going wrong???I know that an UnmarshalException is to do with an IO error occuring while attempting to unmarshal (deserialise) the value returned by a remote method but I can't actually fix it after several attempts. All help is appreciated.
Regards spj2004

Answer 1

I'm not an RMI Expert, but that exception is thrown because the class you are trying to serialize does not implement java.io.Serializable
Try changing this:
public class CopyImpl implements CopyIF{
to:
public class CopyImpl implements CopyIF, java.io.Serializable{