Upload XML as String in ABAP

You can use GUI_UPLOAD function module or IMPORT_FROM_FILE method of CL_XML_DOCUMENT to upload XML document.

Below program use GUI_UPLOAD function module to upload XML document.

*&---------------------------------------------------------------------*
*&      Data Declaration
*&---------------------------------------------------------------------*
DATA: gcl_xml       TYPE REF TO cl_xml_document.
DATA: gv_filename   TYPE string.
DATA: gt_xml        TYPE swxmlcont.
DATA: gv_xml_string TYPE string.
DATA: gv_size       TYPE i.
*&---------------------------------------------------------------------*
*&      start-of-selection
*&---------------------------------------------------------------------*
START-OF-SELECTION.

  CREATE OBJECT gcl_xml.

  gv_filename = 'c:\test.xml'.

*Upload XML file
  CALL FUNCTION 'GUI_UPLOAD'
    EXPORTING
      filename            = gv_filename
      filetype            = 'BIN'
      has_field_separator = ' '
      header_length       = 0
    IMPORTING
      filelength          = gv_size
    TABLES
      data_tab            = gt_xml
    EXCEPTIONS
      OTHERS              = 1.

*Convert uploaded data to string
  CALL FUNCTION 'SCMS_BINARY_TO_STRING'
    EXPORTING
      input_length = gv_size
    IMPORTING
      text_buffer  = gv_xml_string
    TABLES
      binary_tab   = gt_xml
    EXCEPTIONS
      failed       = 1
      OTHERS       = 2.
  IF sy-subrc <> 0.
    MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
            WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
  ENDIF.

**Parses XML String to DOM
  CALL METHOD gcl_xml->parse_string
    EXPORTING
      stream = gv_xml_string.

*Display XML
  CALL METHOD gcl_xml->display.

Below program use IMPORT_FROM_FILE method of CL_XML_DOCUMENT to upload XML document.

*&---------------------------------------------------------------------*
*&      Data Declaration
*&---------------------------------------------------------------------*
DATA: gcl_xml  TYPE REF TO cl_xml_document.
DATA: gv_subrc TYPE sy-subrc.
*&---------------------------------------------------------------------*
*&      start-of-selection
*&---------------------------------------------------------------------*
START-OF-SELECTION.

  CREATE OBJECT gcl_xml.

*Upload XML File
  CALL METHOD gcl_xml->import_from_file
    EXPORTING
      filename = 'c:\test.xml'
    RECEIVING
      retcode  = gv_subrc.

  IF gv_subrc = 0.
*Display XML
    CALL METHOD gcl_xml->display.
  ENDIF.