ABAP Programs:Reading data from a file (presentation server)

REPORT ZSOURCE2604.
* Data declarations for later use
PARAMETERS FILENAME(128) DEFAULT 'c:usersdefaulttestfile.dat'
LOWER CASE.
TABLES CUSTOMERS.
DATA ALL_CUSTOMERS LIKE CUSTOMERS OCCURS 100
WITH HEADER LINE.

CALL FUNCTION 'WS_UPLOAD'
EXPORTING
FILENAME = FILENAME
TABLES
DATA_TAB = ALL_CUSTOMERS
EXCEPTIONS
FILE_OPEN_ERROR = 1
OTHERS = 2.
CASE SY-SUBRC.
WHEN 1.
WRITE 'Error when file opened'.
EXIT.
WHEN 2.
WRITE 'Error during data transfer'.
EXIT.
ENDCASE.
* Display the result
LOOP AT ALL_CUSTOMERS.
WRITE: / ALL_CUSTOMERS-NAME,
ALL_CUSTOMERS-CITY.
ENDLOOP.