Welcome to another ABAP Trapdoors article - the first one posted using my new SCN user. If you are intersted in the older articles, you can find a link list at the bottom of this post.
I've been using asXML for some years now as a convenient way to serialize and deserialize arbitrary ABAP data structures. Some time ago, I learned about IF_SERIALIZABLE_OBJECT and its use to include class instances (aka objects) in an asXML representation as well. A few days ago, I decided to use this technique in a current development project. At the same time, I was trying to use CL_DEMO_OUTPUT_STREAM instead of classic lists as suggested by the online documentation, and since I was supposedly familiar with the basics of using transformations, I focused rather on the usage of this new output technology. I hacked together a small demo programm like this one:
REPORT z_test_serialize.
CLASS lcl_serializable_thingy DEFINITION CREATE PUBLIC.
PUBLIC SECTION.
INTERFACES if_serializable_object.
METHODS constructor
IMPORTING
i_foo TYPE string.
METHODS get_foo
RETURNING
VALUE(r_foo) TYPE string.
PRIVATE SECTION.
DATA g_foo TYPE string.
ENDCLASS.
CLASS lcl_serializable_thingy IMPLEMENTATION.
METHOD constructor.
g_foo = i_foo.
ENDMETHOD.
METHOD get_foo.
r_foo = g_foo.
ENDMETHOD.
ENDCLASS.
CLASS lcl_main DEFINITION CREATE PRIVATE.
PUBLIC SECTION.
CLASS-METHODS run.
ENDCLASS.
CLASS lcl_main IMPLEMENTATION.
METHOD run.
DATA: lr_stream TYPE REF TO cl_demo_output_stream,
l_foo_in TYPE string,
lr_first_thingy TYPE REF TO lcl_serializable_thingy,
l_xml_data TYPE string,
lr_second_thingy TYPE REF TO lcl_serializable_thingy,
l_foo_out TYPE string.
lr_stream = cl_demo_output_stream=>open( ).
SET HANDLER cl_demo_output_html=>handle_output FOR lr_stream.
lr_stream->write_text( iv_text = 'XML Serialization of ABAP Objects Instances'
iv_format = if_demo_output_formats=>heading
iv_level = 1 ).
l_foo_in = |Hello, this is Foo Bar calling from { sy-sysid } client { sy-mandt }.|.
lr_stream->write_data( iv_name = 'Input Data'
ia_value = l_foo_in
iv_format = if_demo_output_formats=>nonprop ).
CREATE OBJECT lr_first_thingy
EXPORTING
i_foo = l_foo_in.
CALL TRANSFORMATION id
SOURCE instance = lr_first_thingy
RESULT xml = l_xml_data.
lr_stream->write_data( iv_name = 'XML Serialization'
ia_value = l_xml_data
iv_format = if_demo_output_formats=>nonprop ).
CALL TRANSFORMATION id
SOURCE xml = l_xml_data
RESULT instance = lr_second_thingy.
l_foo_out = lr_second_thingy->get_foo( ).
lr_stream->write_data( iv_name = 'Output Data'
ia_value = l_foo_out
iv_format = if_demo_output_formats=>nonprop ).
lr_stream->close( ).
ENDMETHOD.
ENDCLASS.
START-OF-SELECTION.
lcl_main=>run( ).
Instead of the expected output (some text, an XML representation of the instance and the same text again), I got - a shortdump. The reference lr_second_thingy was not set after the second transformation - so the deserialization must somehow be broken, right? The debugger quickly revealed that the string variable that was supposed to contain the serialized instance was empty - so it's the serialization that must be broken, then, and not the deserialization? Well, they both are, in a way. To cut straight to the point, here is the faulty code:
CALL TRANSFORMATION id
SOURCE instance = lr_first_thingy
RESULT xml = l_xml_data.
lr_stream->write_data( iv_name = 'XML Serialization'
ia_value = l_xml_data
iv_format = if_demo_output_formats=>nonprop ).
CALL TRANSFORMATION id
SOURCE xml = l_xml_data
RESULT instance = lr_second_thingy.
And here is the corrected version:
CALL TRANSFORMATION id
SOURCE instance = lr_first_thingy
RESULT XML l_xml_data.
lr_stream->write_data( iv_name = 'XML Serialization'
ia_value = l_xml_data
iv_format = if_demo_output_formats=>nonprop ).
CALL TRANSFORMATION id
SOURCE XML l_xml_data
RESULT instance = lr_second_thingy.
Yup, the difference is a single character - or two characters in this case. Without the equals sign, XML is treated as a keyword to denote a variable containing the raw XML data. With the equals sign, something else happens that I have yet to find a sensible and practical use for - at least when used with the identity transformation. You can spot this issue if you use the pretty printer to convert the keywords to upper case - and if you notice the tiny difference between xml and XML.
Older ABAP Trapdoors articles
