2.1.3 Defining utilities for sharing an object reference

Now we will define some utilities for communicating an object reference from the server to the client by converting the object reference into a string using ORB-supplied functions and writing it to a shared file. The client can then read the string from the shared file and convert it back into an object reference. Note that a real application would probably use a higher level service such as a Name Service for passing object references between applications.

1. Create a file called shared.lisp .
2. Enter the following Common Lisp code into the shared.lisp file:

(defparameter *hello-world-ior-file*

  #+Harlequin-PC-Lisp "c:/temp/hello.ior"

  #-Harlequin-PC-Lisp "/tmp/hello.ior")

(defun object-to-file (orb object)

  (with-open-file (st *hello-world-ior-file* :direction :output

                                          :if-exists :supersede)

    (prin1 (op:object_to_string orb object) st)))

(defun file-to-object (orb)

  (with-open-file (st *hello-world-ior-file*)

    (op:string_to_object orb (read st))))

This code does the following:

• object-to-file opens the shared file and uses the op:object_to_string function to convert the object reference into a string, which is then written into the file
• file-to-object performs the inverse operation: it reads the string from the file and uses op:string_to_object to convert the string back into a client-side proxy object
• Save and close the shared.lisp file.
• Add shared.lisp to the defsystem by adding one line of code to the defsys.lisp file, which should then look like this:

(defsystem hello-world-corba-object ()

  :members (

            ("hello-world" :type :idl-file)

            "shared"

            ))

:rules ((:in-order-to :compile "all

         (:requires (:load :previous)))))