CORBA Application Wizard - A Tutorial on usage. Part II

• Download server project - 28 Kb
• Download client project - 30 Kb

Introduction

This is part II of the Using CORBA AppWizard tutorial. The first part of the tutorial dealt with the Application Wizard steps. This part will complete the tutorial by implementing the Stock Quoter application.

Completing the Applications

Now that the framework for the application has been generated and the workspace is display by the IDE, we can add code and complete the Quoter application. Of all the files that are shown in the view only the StdAfx.cpp, StdAfx.h and QuoterServer.cpp contain code. All the others files are basically empty except for displaying the following message:

//DO NOT ENTER ANYTHING HERE !!!!

//THIS WILL BE REPLACED BY CODE ONCE THE *.IDL FILE HAS BEEN COMPILED

So lets get started:

• The IDL File
• The Server Application
• The Client Application
• Running the Application

The IDL File

Now open the Quoter.idl file. It should contain the following:

#ifndef Quoter_module
#define Quoter_module

module Quoter
{
    interface Stock
    {
        
    };

    interface StockFactory
    {
        
    };

};

#endif    //Quoter_module

First we need to define the interfaces. We will start with the Stock interface, where a function that will be used to find out the price of a stock is the first that we will deal with. (The code in bold is what needs to be added).

interface Stock
{
  double price();
};

Each stock also has a name and symbol associated with it, which we can call the attributes of the stock. So lets add these attributes, and so that the user can only enquire about them and not set them we will make them read-only:

interface Stock
{
  double price();
    
    readonly attribute string symbol;
    readonly attribute string full_name;
};

To get the stock object that corresponds to a specific symbol we need to use the StockFactory interface and add a function that takes a symbol as an argument and returns the stock associated with that symbol. However if an invalid symbol is passed as a parameter to this function, then an error will occur. The error raised will be in the form of an exception.

module Quoter
{
  exception Invalid_Stock_Symbol {};
    
  interface Stock
  ....
  interface StockFactory
  {
    Stock get_stock(in string stock_symbol) raises (Invalid_Stock_Symbol);
  };

Now the Quoter.idl can be compiled. The compilation is done by the TAO_IDL compiler. If all goes well the empty files will now contain various forms of code when opened. The code produced in some files is in the form of a skeleton to which you need to add the meat.

The Server Application

Open the QuoterI.cpp and the QuoterI.h files. This is where the interfaces that are found in the Quoter.idl will be implemented. There is no need to open any of the other files e.g. QuoterS.cpp

consists of CORBA related skeleton code, QuoterC.cpp consists of CORBA related stub code and will most likely give you nightmares. First lets look at the QuoterI.h file. The Stock interface is implemented by the Quoter_Stock_i class while the StockFactory interface is implemented by the Quoter_StockFactory_i class. We will first look at the Quoter_Stock_i class and then at the Quoter_StockFactory_i class (again the code in bold is what needs to be entered by you).

class  Quoter_Stock_i : public virtual POA_Quoter::Stock
{
public:
  //Constructor 
  Quoter_Stock_i (const char* symbol, const char* full_name, 
    CORBA::Double price);
  ...

private:
  std::string symbol_;
    std::string full_name_;
    CORBA::Double price_;
}

The StockFactory will only have two stocks: RHAT and MSFT.

//Class Quoter_StockFactory_i
class  Quoter_StockFactory_i : public virtual POA_Quoter::StockFactory
{
public:
   ...

private:
   Quoter_Stock_i rhat_;
     Quoter_Stock_i msft_;

};

Now lets look at the QuoterI.cpp file where the functions shown above will be implemented.

Lets concentrate on the Quoter_Stock_i class. First the constructor.

Quoter_Stock_i::Quoter_Stock_i (const char *symbol, const char *full_name, 
    CORBA::Double price)
  : symbol_ (symbol), full_name_ (full_name), price_ (price)
{
}

First we will implement the functions declared in the Quoter_Stock_i class:

• The symbol() function. This function returns the symbol associated with the stock.

char* Quoter_Stock_i::symbol() throw (CORBA::SystemException)
{
  return CORBA::string_dup(this->symbol_.c_str());
}

• The full_name() function. This function returns the name associated with the stock.

char* Quoter_Stock_i::full_name() throw (CORBA::SystemException)
{
  return CORBA::string_dup(this->full_name_.c_str());
}

• The price() function. This function returns the current price of the stock.

CORBA::Double Quoter_Stock_i::price() throw (CORBA::SystemException)
{
  return this->price_;
}

Now it is the turn of the Quoter_StockFactory_i class. There is only one function, namely get_stock() that needs implementing.

Quoter::Stock_ptr Quoter_StockFactory_i::get_stock(
        const char * stock_symbol) throw 
    (CORBA::SystemException, Quoter::Invalid_Stock_Symbol)
{
  if (strcmp (symbol, "RHAT") == 0)
  {
    return this->rhat_._this();
  }
    else if (strcmp (symbol, "MSFT") == 0)
    {
    return this->msft_._this ();
  }
  throw Quoter::Invalid_Stock_Symbol ();

}

The Quoter_StockFactory_i constructor also needs some changes.

Quoter_StockFactory_i::Quoter_StockFactory_i()
  : rhat_("RHAT", "RedHat, Inc.", 210), msft_("MSFT", "Microsoft, Inc.", 91) 
{
}

Finally we turn to the QuoterServer.cpp file (QuoterServer is the name I gave to the project, so whatever you named your project look for a file with that name and a .cpp extension) and look at the main() function.

  //create object here
  Quoter_StockFactory_i stock_factory_i;

  // Activate it to obtain the object reference
  Quoter::StockFactory_var stock_factory = stock_factory_i._this();

    CORBA::String_var ior = orb->object_to_string(stock_factory.in());
    cout << ior.in() << endl;

Now it is time to build the server application. But first a warning, don't go and click on the Build toolbar button! The problem is that the Quoter.idl file will be compiled again and any changes that you have made to the QuoterI.h and QuoterI.cpp files will have been replaced by the skeleton code produced by the TAO_IDL compiler. Rather highlight the StdAfx.cpp file and compile it. Follow that by the separate compilation of the QuoterI.cpp and QuoterServer.cpp files respectively. Now you can click on the Build toolbar button.

The Client Application

The idl file is the same as that for the Server application. So just copy the Quoter.idl file from the directory of the Server application and copy it into the directory of the Client application. Open the Quoter.idl file and compile it. Once again the TAO_IDL compiler will be used. Initially the QuoterC.cpp file will be empty but after compilation will contain the CORBA stub code. For the client side of the Stock Quoter application we only need to look at the main() function (Remember the code in bold is what you need to enter).

  //You code goes here!
  Quoter::StockFactory_var factory = 
    Quoter::StockFactory::_narrow(obj.in());
  for (int i = 2; i != argc; i++)
  {
    try
    {
      Quoter::Stock_var stock = factory->get_stock(argv[i]);
      CORBA::String_var name = stock->full_name();
      CORBA::Double price = stock->price();

      cout << "The price of stock in \"" << name.in() << "\" is $" 
        << price << endl;
    }
    catch(Quoter::Invalid_Stock_Symbol&)
    {
      cerr << "Invalid stock symbol <" << argv[i] << ">" << endl;
    }
  }
    orb->destroy();

Lets now build the client application, but in comparison to the server application one can click on the Build toolbar button immediately.

Running the Application

Now that you have compiled and built both the server and client applications, it is time to run the Stock Quoter application and see if everything works. Open two DOS prompt windows. In the first window write:

server > ior_file

and leave the window open. The image below shows what I typed on my computer.

In the second window write:

client file://ior_file MSFT RHAT HALO

and then press Return. The image below shows the command and result on my computer. Note that we didn't implement HALO as a stock in the StockFactory and therefore the error message.

Comments

If you have any comments or find any bugs please let me know.

History

• 3 November 2003 - First public release.