请问一个对象序列化的问题

[littledapan]

小弟要对一个远程的方法尽心调用.服务端的代码如下,但是发现Hashtable无法返回，请问我该怎么做?
public class ServiceManagerImpl extends GridServiceImpl implements erviceManagerPortType
{

.......

public Object list() throws java.rmi.RemoteException
{
list_sql_str=new String("select * from services;");
try{
st=con.createStatement();
rs=st.executeQuery(list_sql_str);
System.out.println("list services");
while(rs.next())
{
this.hash_gsh=new String(rs.getString(1));
System.out.println(""+hash_gsh);
this.WSDL=new String(rs.getString(3));
System.out.println(" "+WSDL);
this.hash_jsp=new String(rs.getString(5));
System.out.println(" "+hash_jsp);
this.hash_sla=new String(rs.getString(4));
System.out.println(" "+hash_sla);

if (!service_list.containsKey(hash_gsh))
service_list.put(hash_gsh,new service_hash_content(WSDL,hash_jsp,hash_sla,hash_name));
}
} catch (SQLException E)
{
System.out.println("SQLException: " + E.getMessage());
System.out.println("SQLState: " + E.getSQLState());
System.out.println("VendorError: " + E.getErrorCode());
}
return service_list;
}
......