21. **JSON**: handling JSON data
********************************

JSON is a format often used on the web to communicate between a server
and a browser, or between servers. It plays a similar role to XML, but
is much lighter in terms of size. On the other hand, it doesn’t
provide advanced features like validation which XML provides.

The package **GNATCOLL.JSON** provides an Ada for creating JSON data,
or parse such data that your application receives.

Most JSON data will generally start with an object, on which
attributes can be set. The value for the attributes are also JSON
data.

Here is an example of use:

   pragma Ada_05;
   with GNATCOLL.JSON;   use GNATCOLL.JSON;
   with Ada.Text_IO;     use Ada.Text_IO;

   procedure JSON_Test is
      MyObj : JSON_Value := Create_Object;
   begin
      MyObj.Set_Field ("field1", Create (1));
      MyObj.Set_Field ("name", "theName");

      --  Now print the value
      Put_Line (MyObj.Write);
   end JSON_Test;

This example used the Ada05 dot notation to call the primitive
operations, but would also work using the more traditional prefix
notation.

It is also possible to create JSON arrays. These are not tagged types,
so the prefix notation has to be used. Here is a further example that
sets another field in the object we had before:

   declare
      MyArr : JSON_Array := Empty_Array;
   begin
      Append (MyArr, Create (1));
      Append (MyArr, Create ("aString"));

      MyObj.Set_Field ("vals", MyArr);
   end;

GNATColl automatically takes care of memory management, and all
allocated memory is automatically freed when the object is no longer
needed.