5.2 Transforming your XML Documents

The following sections illustrate how to perform both character-based and element-based transformations, using an object book.

The steps included in this section include:

• adding serialization support (for more information, see Chapter 3)

• creating a book object and serializing it to a file using an XML stream that applies a transformation to make the resulting XML more readable

• reading the file back in and restoring the book object using an XML stream that applies a transformation to restore the original XML format

• printing out both the original XML streams data for the book object and its more readable, transformed version

The object book holds an author name and a book title.

First, you will instantiate book, and add serialization support. This process is identical for both transformations.

class book 
{
   public:
     book ();
     book (const RWCString& title, const RWCString& author);
   private:
     RWCString title_;
     RWCString author_;
};

As described in the example in Chapter 3, you must add macros to the header and implementation files to prepare the object for serialization.

• To the header file, add the macro RW_DECLARE_VIRTUAL_STREAM_FNS(), which defines the streamContents() member function:

class book 
{
   RW_DECLARE_VIRTUAL_STREAM_FNS(book)

   public:
     book ();
     book (const RWCString& title, const RWCString& author);

   private:
     RWCString title_;
     RWCString author_;
};
Add to the header file:
            // Add serialization support 
        RW_DECLARE_STREAMABLE_AS_SELF(book)
        RW_DECLARE_STREAMABLE_POINTER(book)

• To the implementation file, first add macros that define insertion and extraction operators for the class members:

// Define how book will be serialized
RW_BEGIN_STREAM_CONTENTS(book)
   RW_STREAM_ATTR_MEMBER(title,title_)
   RW_STREAM_ATTR_MEMBER(author,author_)
RW_END_STREAM_CONTENTS

Then add macros that allow the book object itself to be serialized as a pointer reference:

// Allow a reference to a book to be serialized         
RW_DEFINE_STREAMABLE_POINTER(book)
RW_DEFINE_STREAMABLE_AS_SELF(book)

Next, you serialize your book object out to a file. Because the XML format generated by XML streams is difficult to read, transform the output stream into a more readable format.

Each of the following sections considers first a character-based C++ transformation, followed by an element-based C++ transformation.

int main()
{
   using std::ofstream;                                        //1
   using std::ifstream;
   using std::cout;
   using std::endl;

   book book1("To Love and Be Wise","Josephine Tey");          //2
   book book2;

   MyInStreamTransform inTransform;                            //3
   MyOutStreamTransform outTransform;                          //4

   {
     ofstream fout("book.xml");                                //5

     RWObjectOutputStream out =                                //6
          RWTTransformObjectOutputStreamImp<MyOutStreamTransform>
            ::make(fout,outTransform);
     out << book1;                                            //7
     out.flush();                                               //8   
}

int main()
{
   using std::ofstream;                                         //1
   using std::ifstream;
   using std::cout;
   using std::endl;

   book book1("To Love and Be Wise","Josephine Tey");           //2
   book book2;

   MyInParsedTransform inTransform;                             //3
   MyOutParsedTransform outTransform;                           //4

   {
     ofstream fout("book.xml");                                 //5

     RWObjectOutputStream out =                                 //6
       RWTParsedObjectOutputStreamImp<MyOutParsedTransform>
         ::make(fout,outTransform);
     out << book1;                                              //7
     out.flush();                                               //8
   }

At this point you have written the book object XML data to the file book.xml. Next you are ready to restore the object, which involves:

• reading in the file book.xml

• transforming the XML back to the form required by XML streams

• restoring the object as book2

   {
     ifstream fin("book.xml");                                  //1

     RWObjectInputStream in =                                   //2
       RWTTransformObjectInputStreamImp<MyInStreamTransform>
         ::make(fin,inTransform);
     in >> book2;                                               //3
   }

   {
     ifstream fin("book.xml");                                  //1

     RWObjectInputStream in =                                   //2
       RWTParsedObjectInputStreamImp<MyInParsedTransform>
         ::make(fin,inTransform);
     in >> book2;                                               //3
   }

Finally, the example writes to standard out two forms of the serialized object:

• the transformed, more readable version

• the form created by the XML serialization and expected by XML streams when the object is restored

   {
     RWObjectOutputStream out =                                 //1
       RWTTransformObjectOutputStreamImp<MyOutStreamTransform>
         ::make(cout,outTransform);
     out << book2;                                              //2
   }
   cout << endl;
   {
     RWObjectOutputStream out =                                 //3
       RWXmlObjectOutputStreamImp::make(cout);
     out << book2;                                              //4
   }
   return 0;
}

Here is the resulting output:

With transformation:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>  <rw:nested_object rw:class="book"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
  xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" 
  xmlns:rw="http://www.roguewave.com/xmlstream">
    <rw:member rw:name="title" xsi:type="xsd:string">To Love 
        and Be Wise</rw:member>
    <rw:member rw:name="author" xsi:type="xsd:string">
        Josephine Tey</rw:member></rw:nested_object>

Without transformation:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <rw:nested_object rw:class="book"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
  xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
  xmlns:rw="http://www.roguewave.com/xmlstream">
    <rw:member rw:name="title" xsi:type="xsd:string">To Love and Be
        Wise</rw:member>
    <rw:member rw:name="author" xsi:type="xsd:string">Josephine
        Tey</rw:member></rw:nested_object>

   {
     RWObjectOutputStream out =                                 //1
       RWTParsedObjectOutputStreamImp<MyOutParsedTransform>
         ::make(cout,outTransform);
     out << book2;                                              //2
   }
   cout << endl;
   {
     RWObjectOutputStream out =                                 //3
       RWXmlObjectOutputStreamImp::make(cout);
     out << book2;                                              //4
   }
   return 0;
}

Here is the resulting output:

With transformation:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<book xmlns:rw="http://www.roguewave.com/xmlstream" 
xsi:type="book" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance">
<title xsi:type="xsd:string">To Love and Be Wise</title>
<author xsi:type="xsd:string">Josephine Tey</author>
</book>

Without transformation:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>>
  <rw:nested_object rw:class="book" 
  xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
  xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"  
  xmlns:rw="http://www.roguewave.com/xmlstream">
    <rw:member rw:name="title" xsi:type="xsd:string">To Love and Be
        Wise</rw:member>
    <rw:member rw:name="author" xsi:type="xsd:string">Josephine
        Tey</rw:member></rw:nested_object>

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