Wood J. Object-Oriented Programming with ABAP Objects

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Case Study: Building an XML Document | 12.4

* Use the private constructor to create an instance

* of a DOM-based XML document:

CREATE OBJECT re.list.

* Build the "ReadingLisf root element:

re_list->list_node -

re_list->xml_document->create_simple_element(

name - 'ReadingLisf

parent - re_list->xml_document ).

* Build the "Topic" element:

re_list->xml_document->create_simple_element(

name - 'Topic*

value - im_topic

parent - re_list->list_node ).

* Build the "RecommendedBooks" element:

re_list->books_node -

re_list->xml_document->create_simple_element(

name - 'RecommendedBooks*

parent - re_list->list_node ).

ENDMETHOD.

ENOCLASS.

Listing 12.6 Creating a New Reading List Document

In the implementation code shown in Listing 12.6, notice that a reference to the

iXMI. factory attribute is obtained inside the class_constructor method as

opposed to the instance constructor method. Here, it made sense to share the

factory attribute across all object instances. Similarly, a reference to the iXML

stream factory is obtained in the stream_factory class attribute. You will see how

I/O streams are used a little bit later on.

Users can create a new reading list by calling the class method create_new_l ist.

This method defers the creation of the IF_IXML_D0CUMENT instance (i.e.. attribute

xml.document) to the private constructor method. After the DOM-based docu-

ment is created, you can create the <ReadingList> root element using the

instance method CREATE_SIMPLE_ELEMENT of interface IF_lXML_DOCUMENT. This

method returns a reference to an I F_I

XML_ELEMENT

object that is stored in the

1 ist_node instance attribute. From here, you can recursively call the

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Working with XML

CREATE_SIMPLE_ELEMENT method to create the child elements <Topfc> and <Rec-

ommended6ooks> for the <Readi ngLi st> root node. The topic of the reading list is

provided via the im_topic importing parameter of method create_new_1 ist.

The method create_new_l ist returns an instance of type lcl_reading_l ist. Ini-

tially, this reading list is empty. To add books to the reading list, users must call

the instance method add_book whose implementation is shown in Listing 12.7.

CLASS lc!_reading_Iist IMPLEMENTATION.

METHOO add_book.

* Method-Local Data Declarations:

DATA: 1r_book_node TYPE REF TO if_ixml_element.

lv_author TYPE string.

* 8uild the new "Book" element:

lr_book_node -

xml_document->create_element( name- 'Book* ).

1r_book_node->set_attri bute(

name - 'isbn' value - im_isbn ).

xml_document->create_simple_element(

name - 'Title'

value - im_title

parent - lr_book_node ).

xml_document->create_simple_element(

name - 'Publisher'

value - im_publisher

parent - lr_book_node ).

LOOP AT im_authors INTO lv_author.

xml_document->create_s1mple_element(

name - 'Author'

value - lv_author

parent - lr_book_node ).

ENDLCOP.

* Add the "Book" element to the book collection:

books_node->append_child( lr_book_node ).

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Case Study: Building an XML Document | 12.4

ENDMETHOD.

ENDCLASS.

Listing 12.7 Adding Books to the Reading List

This method starts off by generating a new <Book> element using the

CREATE.ELEMENT method of interface IF_IXML_DOCUMENT. At this point, this is a

standalone element that is not associated with the reading list. However, before

appending the <Book> element to the list, the relevant attribute and child ele-

ments need to be generated for the book. Here, the isbn attribute is set using the

instance method SET_ATTRIBUTE defined in interface IF_IXML_ELEMENT. Next, the

<Title>, <Publisher>, and <Author> elements are set using method CREATE.

SIMPLE.ELEMENT. Finally, after the <8ook> element is constructed, it is appended

to the <RecommendedBooks> node by calling instance method APPEND_CHI

on the

books.node instance attribute.

After the reading list has been generated, we want to be able to save the list as an

XML file on the user's workstation. Listing 12.8 shows how a public instance

method called serial ize has been defined for this purpose.

CLASS lcl_reading_list IMPLEMENTATION.

METHOD serialize.

* Method-Local Data Declarations:

OATA: lr_ostream TYPE REF TO if_ixml_ostream.

It_xml TYPE TABLE OF ty_xml_line.

lr_renderer TYPE REF TO if_ixml_renderer.

lv_retcode TYPE i.

Iv_filesize TYPE i.

Iv_filename TYPE string.

* Prompt the user for the name of the output file:

lv_filename - get.filename( C0_SAVE_DIAL0G ).

* Create an XML output stream:

lr_ostream -

stream_factory->create_ostream_itable(

table - lt_xml ).

* Render the XML document into the XML output stream:

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12 | Working with XML

lr_renderer -

factory->create_renderer(

ostream - lr_ostream

document - xml_document >.

lv_retcode - 1r_renderer->render( ).

IF 1v_retcode NE 0.

RAISE EXCEPTION TYPE cx_sy_ft1e_io

EXPORTING

textid - cx_sy_file_io->write_error

filename - lv_filename.

ENOIF.

Download the XML file to the user's workstation:

lv_filesize - 1r_ostream->get_num_written_raw( ).

CALL METHOD cl_gui_frontend_services->gui_download

EXPORTING

bin_filesize - lv_filesize

filename - lv_filename

filetype - 'BIN-

CHANGING

data_tab - lt_xml

EXCEPTIONS

others - 24.

IF sy-subrc NE 0.

RAISE EXCEPTION TYPE cx_sy_file_io

EXPORTING

textid

cx_sy_fi1e_i o->cx_sy_f i1e_access_error

filename - lv_filename.

ENDIF.

ENDMETHOD.

METHOD get_filename.

Method-Local Data Declarations:

DATA: 1t_files TYPE filetable.

1v_retcode TYPE i.

1v_path TYPE string.

1v_ful1 path TYPE string.

Let the user select a file from his workstation:

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Case Study: Building an XML Document

CASE im_dia1og_type.

WHEN C0_0PEN_DIAL0G.

CALL METHOD

cl_gui_frontend_services->file_open_dialog

CHANGING

file_table - 1t_files

rc - lv_retcode

EXCEPTIONS

others - 5.

READ TA8LE 1t_files INDEX 1 into re_filename.

WHEN C0_SAVE_DIAL0G.

CALL METHOD

cl_gui_frontend_services->file_save_dialog

CHANGING

filename - re_filename

path - lv_path

full path - lv_fullpath

EXCEPTIONS

others - 4.

ENDCASE.

ENDMETHOD.

ENOCLASS.

Listing 12.8 Serializing the Reading List to an XML File

The first task of method serialize is to create an output stream instance. The

term stream refers to a sequence of bytes. Therefore, an iXML output stream

refers to a sequence of bytes that are being rendered as an ABAP data object. In

method serialize, the raw XMI. content is bound into an internal table variable

called l t_xml. After the output stream is created, the next step is to render (or con-

vert) the DOM-based XML document into that output stream object. This is

achieved via an XML renderer object that implements the IF_lXML_RENDERER

interface. This interface defines an instance method called RENDER that is used to

serialize the XML document into the l t_xml internal table variable. Finally, the

standard CL_GUI_FRONTEND_SERVICES class features are used to allow users to save

the XML file to their local workstations.

The report program ZIXMLWRITER shown in Listing 12.9 demonstrates how to

use the lcl_reading_list class to create and serialize a reading list document.

It begins by creating a new ABAP Programming reading list using the create_

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12 | Working with XML

newjist creational method. Next, the title ABAP Basics is added to the list by

calling method add_book. Finally, the reading list is saved to a file by calling

method serial i/e. In the next section, you will learn how to parse this XML file

using the parser provided with the iXML library.

REPORT zixmlwriter.

INCLUDE: zxmllib. "Reading List ADT

DATA: gr_reading_1ist TYPE REF TO lcl_reading_list.

1t_authors TYPE string_table.

START-OF-SELECT ION.

* Create a new "ABAP Programming" reading list:

gr_reading_l1st -

lcl_reading_list->create_new_list(

'ABAP Programming' ).

* Add a book to the 11st:

APPEND 'Guenther Faerber* TO lt_authors.

APPEND 'Julia Kirchner' TO lt_authors.

CALL METHOD gr_reading_list->add_book

EXPORTING

im_isbn - '978-1-59229-153-3'

im_title - 'ABAP Basics*

im_authors - lt_authors

im_publisher - 'SAP PRESS'.

* Serialize the generated XML file:

gr_reading_list->serialize( ).

Listing 12.9 Sample Program to Test the Creation of a Reading List

12.5 Case Study: Reading an XAAL Document

In the previous section, you learned how to interact with the DOM API to gener-

ate a brand new XML document. You also saw how to serialize the XML docu-

ment into an output file. Frequently, you may want to read and/or modify that

file again later. To read the XML File back into context, you must enlist the aid of

the XML parser. Listing 12.10 shows how to implement this logic inside of the

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Case Study: Reading an XML Document 12-5

crcational class method create_from_file, which delegates much of the heavy

lifting to the private helper method uploadj ist_file.

CLASS lcl_readi ng_list IMPLEMENTATION.

METHOD create_from_file.

* Create an instance of the reading list:

CREATE OBJECT rejist.

* Upload a pre-existing reading list file into context:

re_list->upload_list_file( ).

* Obtain references to the index nodes:

re_list->list_node -

re_list->xml_document->get_root_element( ).

re_list->books_node -

re_llst->1ist_node->find_from_name(

name - 'RecommendedBooks' ).

ENDMETHOD.

METHOD uploadjist_flie.

* Method-Local Data Declarations:

DATA: lt.files TYPE filetable.

1v_retcode TYPE i.

lv_filename TYPE string.

1v_filesize TYPE i.

1t_xml TYPE TABLE

OF ty_xml_line.

lr_istream TYPE REF TO if_1xml_1stream.

lr_parser TYPE REF TO if_ixml_parser.

1r_parse_error TYPE REF TO if_ixml_parse_error.

1v_error_code TYPE i.

lv_reason TYPE string,

lvjine TYPE i.

1v_column TYPE i.

* Let the user select a file on his workstation:

1v_filename - get_filename( C0_0PEN_DIAL06 ).

* Upload the file from the client's workstation:

CALL METHOD cl_gui_frontend_services->gui_upload

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12 | Working with XML

EXPORTING

filename - lv_filename

filetype - 'BIN'

IMPORTING

filelength - lv_filesize

CHANGING

data_tab - lt_xml

EXCEPTIONS

others - 19.

Convert the raw XML content into an XML input stream:

lr_istream -

stream_factory->create_istream_i tablet

table - lt.xml

size - lv_filesize ).

IF 1r_istream IS INITIAL.

RAISE EXCEPTION TYPE cx_ixml_parse_error

EXPORTING

textid -

cx_ixml_parse_error->cx_ixml_parse_error

code - sy-subrc

reason - 'Could not read the XML list file!'.

ENOIF.

Parse the XML file into a DOM-based XML document:

lr_parser -

factory->create_parser(

stream_factory - stream_factory

istream - lr_istream

document - xml_document ).

Check the results:

lv_retcode - 1r_parser->parse( ).

IF 1v_retcode NE 0.

Propagate the parse exception to the caller:

1r_parse_error - 1r_parser->get_error( 0 ).

1v_error_code - 1r_parse_error->get_number( ).

lv_reason - 1r_parse_error->get_reason( ).

lv_line - 1r_parse_error->get_)ine( ).

lv_co)umn - 1r_parse_error->get_column( ).

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Case Study: Reading an XML Document 12.5

RAISE EXCEPTION TYPE cx_ixml_parse_error

EXPORTING

textid -

cx_ixml_parse_error->cx_ixml_parse_error

code - lv_error_code

reason - lv_reason

line - lv_line

column - lv_column.

ENOIF.

ENDMETHOD.

ENOCLASS.

Listing 12.10 Parsing an XML-8ased Reading List File

Listing 12.10 again uses the standard class CL_GUI_FRONTEND_SERVICES to read the

XML file into an internal table variable called I t_xml. Next, an input stream object

is created that will be used to feed the raw input from the XML file into the XML

parser. After that, a reference to an XML parser instance is obtained that imple-

ments the IF_IXML_PARSER interface. Finally, the PARSE method defined in the

IF_IXHL_PARSER interface is used to parse the XML document. This method pro-

duces a return code that indicates whether or not the parser was able to success-

fully parse the document. In the event that there are parsing errors (due to mal-

formed XML content, for instance), you can call the GET_ERROR method to obtain

a reference to an object that implements the I F_IXML_PARSE_ERROR interface. This

object provides various methods that provide details about the error such as the

line number/column where the error occurred, a text-based description of the

error, and so on.

If there are no errors during the parsing process, the generated DOM-based XML

document will be stored in the xml_document instance attribute. For convenience,

the create_from_f

le method also looks up the <ReadingList> and <Recommended

Books> elements and stores references to them inside the instance attributes

l ist_node and books_node, respectively. Caching this information makes it easier

to modify the XML document later via public instance methods, and so on.

To verify that the XML document is parsing correctly, a di spl ay method has been

implemented that can be used to display the derived XML document in a browser

window. This display functionality is driven by the standard function module

SDI XML_DOM_TO_SCREEN (see Listing 12.11).

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12 | Working with XML

CLASS 1c1_read1ng_l1st IMPLEMENTATION.

METHOO display.

* Display the XHL document in a browser:

CALL FUNCTION 'SOIXML_DOM_TO_SCREEN'

EXPORTING

document - xml_document

EXCEPTIONS

no_document - 1

others - 2.

ENDMETHOD.

ENDCLASS.

Listing 12.11 Displaying the Reading List File in a 8rowser

The report program ZIXMLREADER shown in Listing 12.12 shows how the updated

lcl_reading_l ist class can be used to read a pre-existing XML file into memoiy.

After the DOM-based XML document is loaded, the public add_book method can

be called to add additional books to the list. The updated document is displayed

in a browser window via the call to method display (see Figure 12.4).

REPORT zixmlreader.

INCLUDE: zxmllib. "Reading List ADT

DATA: gr_reading_list TYPE REF TO lcl_reading_1ist.

lt_authors TYPE string_table.

START-OF-SELECT ION.

* Read an existing reading list document into context:

gr_reading_list -

lcl_reading_list->create_from_file( ).

* Add another book to the list:

APPEND 'Horst Keller' TO lt_authors.

CALL METHOD gr_reading_list->add_book

EXPORTING

im_isbn - '978-1-59229-039-0'

im_ti11e - 'The Official ABAP Reference'

im_authors - lt_authors

324