ABAP_to_the_Future

7
Exception Classes and Design by Contract
CATCH ycx_monster_exception INTO lcx_monster_exception.
handle_this_exception( lcx_monster_exception ).
CATCH ycx_monster_exception_mc
INTO lcx_monster_exception_mc.
handle_that_exception( lcx_monster_exception_mc ).
CLEANUP.
cleanup_main_method( ).
ENDTRY.
Listing 7.3 TRY/CATCH/CLEANUP
In Listing 7.3, you’re passing the exception object into the HANDLE_THIS_EXCEP-
TION method. Because this is just a standa rd instance of an ABAP class, you can
query all the class attributes in your handler method (e.g., get the error text and
any supplementary data). Meanwhile, to raise the exception in the first place, you
would write code similar to that in Listing 7.4 inside the DO_SOMETHING method.
RAISE EXCEPTION TYPE zcx_monster_exceptions
EXPORTING
wibbly_wobbly_woos = ld_www_count.
Listing 7.4 Exporting Vital Information while Raising an Exception
7.2.4 Cleaning Up after the Exception Is Raised
The CLEANUP command seems to be one of the most widely misunderstood parts
of the whole class-based exception fram ework. Many progra mmers try it once,
conclude it doesn’t work, and then never look at it again. The idea behind the
CLEANUP construct is that at the start of any given routine, the data is in a consistent
state. The routine merrily starts changing some data values, making the data
temporarily inconsistent, and if all goes well the routine will fix up the data again
before the routine finishes. However, if an error occurs halfway through the routine,
then the second half (which fixes up the data) never happens.
Consider the code in Listing 7.5, which is all about conducting an operation to
replace a monster’s head with a new one. If something goes wrong during the
operation (e.g., a power failure), then whatyou want is to abort the operation and
reattach the old head.
METHOD head_swap_operation.
TRY .
mo_monster->remove_current_head( ).
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