SAP 如何提供 RESTful Web 服务(2) - ABAP 与 JSON

系列文章索引

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SAP 如何提供 RESTful Web 服务？
SAP 如何提供 RESTful Web 服务(2) - ABAP 与 JSON
SAP 如何提供 RESTful Web 服务(3) - Rest 路径处理

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上一篇介绍了 SAP ABAP 提供 RESTful web service 从技术层面需要解决的三个问题：

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• SAP 对外提供 Http Service
• 在 SAP 端解决诸如 authentication，cookie, session 等 Http server 必须解决的问题
• SAP 端实现对响应 (response）以 json 格式返回给客户端，对客户端 json 格式的请求（request）解析并处理

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本篇接着上一篇，介绍如何实现 ABAP 对象 与 JSON 互转。ABAP 与 JSON 互转有多种方法，本篇介绍两个类进行序列化和反序列化的方法：

• CL_TREX_JSON_SERIALIZER ：将 ABAP 内表转换为 json 格式
• CL_TREX_JSON_DESERIALIZER：json 转换为 ABAP 内表

这两个类有一点点问题，序列化生成的格式 key 没有引号，可能导致外部解析的失败。比如

[
    {
        id: "001",
        name: "Stone"
    },
    {
        id: "002",
        name: "Brown"
    }
]

而我们需要的是下面的格式：

[
    {
        "id": "001",
        "name": "Stone"
    },
    {
        "id": "002",
        "name": "Brown"
    }
]

所以需要对两个类进行改造，以符合自己的需求。首先我们使用事务码 SE24 将 CL_TREX_JSON_SERIALIZER 类拷贝一个新类，另存为 ZCL_TREX_JSON_SERIALIZER，然后将 RECURSE() 方法做两点改变：

填加语句：

注释掉 concatenate 语句，改写为下面的语句。就是在 -name 两边加上双引号 ：

完整的 RECURSE() 方法代码如下：

METHOD recurse.

  DATA:
  l_type  TYPE c ,
  l_comps TYPE i ,
  l_lines TYPE i ,
  l_index TYPE i ,
  l_value TYPE string .
  FIELD-SYMBOLS:
     TYPE ANY TABLE ,
     TYPE ANY .

  DESCRIBE FIELD data TYPE l_type COMPONENTS l_comps .

  IF l_type = cl_abap_typedescr=>typekind_table .
*   itab -> array
    APPEND '[' TO me->fragments .
    ASSIGN data TO  .
    l_lines = LINES(  ) .
    LOOP AT  ASSIGNING  .
      ADD 1 TO l_index .
      recurse(  ) .
      IF l_index < l_lines .
        APPEND c_comma TO me->fragments .
      ENDIF .
    ENDLOOP .
    APPEND ']' TO fragments .
  ELSE .
    IF l_comps IS INITIAL .
*     field -> scalar
*     todo: format
      l_value = data .
      REPLACE ALL OCCURRENCES OF '\' IN l_value WITH '\\' .
      REPLACE ALL OCCURRENCES OF '''' IN l_value WITH '\''' .
      REPLACE ALL OCCURRENCES OF '"' IN l_value WITH '\"' .
      REPLACE ALL OCCURRENCES OF '&' IN l_value WITH '\&' .
      REPLACE ALL OCCURRENCES OF cl_abap_char_utilities=>cr_lf IN l_value WITH '\r\n' .
      REPLACE ALL OCCURRENCES OF cl_abap_char_utilities=>newline IN l_value WITH '\n' .
      REPLACE ALL OCCURRENCES OF cl_abap_char_utilities=>horizontal_tab IN l_value WITH '\t' .
      REPLACE ALL OCCURRENCES OF cl_abap_char_utilities=>backspace IN l_value WITH '\b' .
      REPLACE ALL OCCURRENCES OF cl_abap_char_utilities=>form_feed IN l_value WITH '\f' .
      CONDENSE l_value.
      CONCATENATE '"' l_value '"' INTO l_value .
      APPEND l_value TO me->fragments .
    ELSE .
*     structure -> object
      DATA l_typedescr TYPE REF TO cl_abap_structdescr .
      FIELD-SYMBOLS  TYPE abap_compdescr .

      APPEND '{' TO me->fragments .
      l_typedescr ?= cl_abap_typedescr=>describe_by_data( data ) .
      LOOP AT l_typedescr->components ASSIGNING  .
        l_index = sy-tabix .
*        CONCATENATE -name c_colon INTO l_value .
        CONCATENATE '"' -name '"' c_colon INTO l_value.
        TRANSLATE l_value TO LOWER CASE .
        APPEND l_value TO me->fragments .
        ASSIGN COMPONENT -name OF STRUCTURE data TO  .
        recurse(  ) .
        IF l_index < l_comps .
          APPEND c_comma TO me->fragments .
        ENDIF .
      ENDLOOP .
      APPEND '}' TO me->fragments .
    ENDIF .
  ENDIF .

ENDMETHOD.

相对应地， 将 CL_TREX_JSON_DESERIALIZER 拷贝成为 ZCL_TREX_JSON_DESERIALIZER，并且对 deserialize_object 方法做两点变更 (网上有一个做好的图片，我就直接贴图了)：

图片来源：https://archive.sap.com/image/665574

完成后，deserialize_object 方法的完整代码如下：

METHOD deserialize_object.
  DATA:
  l_node_type TYPE REF TO cl_abap_typedescr ,
  l_ref TYPE REF TO object .

  ADD 1 TO offset . "skip {

  l_node_type = cl_abap_typedescr=>describe_by_data( node ) .

* prepare for dynamic access
  CASE l_node_type->kind .
    WHEN cl_abap_typedescr=>kind_ref .
      l_ref = node .
    WHEN cl_abap_typedescr=>kind_struct .

    WHEN OTHERS .
      RAISE EXCEPTION TYPE cx_trex_serialization .
  ENDCASE .

  DATA:
    l_done TYPE abap_bool ,
    l_len TYPE i ,
    l_name TYPE string .

* handle each component
  WHILE l_done = abap_false .
    "find next key
    FIND REGEX '"(\w+)\s*":' IN SECTION OFFSET offset OF json
      MATCH OFFSET offset MATCH LENGTH l_len
      SUBMATCHES l_name .
    IF sy-subrc <> 0 .
      RAISE EXCEPTION TYPE cx_trex_serialization .
    ENDIF .
    ADD l_len TO offset .

    FIELD-SYMBOLS  TYPE ANY .

*   dynamic binding to component
    TRANSLATE l_name TO UPPER CASE .
    CASE l_node_type->kind .
      WHEN cl_abap_typedescr=>kind_ref .
        ASSIGN l_ref->(l_name) TO  .
      WHEN cl_abap_typedescr=>kind_struct .
        ASSIGN COMPONENT l_name OF STRUCTURE node TO  .
        IF sy-subrc <> 0.
          CONTINUE.
        ENDIF.

      WHEN OTHERS .
        RAISE EXCEPTION TYPE cx_trex_serialization .
    ENDCASE .

    DATA:
      l_comp_type TYPE REF TO cl_abap_typedescr ,
      l_ref_type TYPE REF TO cl_abap_refdescr .

*   check component type
    l_comp_type = cl_abap_typedescr=>describe_by_data(  ) .
    CASE l_comp_type->kind .
*     create instance if it's an oref
      WHEN cl_abap_typedescr=>kind_ref .
        l_ref_type ?= l_comp_type .
        l_comp_type = l_ref_type->get_referenced_type( ) .
        CREATE OBJECT  TYPE (l_comp_type->absolute_name) .
    ENDCASE .

*   deserialize current component
    deserialize_node(
      EXPORTING
        json = json
      CHANGING
        offset = offset
        node =  ) .

    FIND REGEX ',|\}' IN SECTION OFFSET offset OF json MATCH OFFSET offset .
    IF sy-subrc <> 0 .
      RAISE EXCEPTION TYPE cx_trex_serialization .
    ENDIF .

    IF json+offset(1) = '}' .
      l_done = abap_true .
    ENDIF .
    ADD 1 TO offset .
  ENDWHILE .

ENDMETHOD.

示例

调用 ZCL_TREX_JSON_SERIALIZER 实现序列化以及调用 ZCL_TREX_JSON_DESERIALIZER 实现反序列化的代码如下：

REPORT  zabap_json .

DATA: serializer TYPE REF TO zcl_trex_json_serializer,
      lv_json TYPE string.

DATA: BEGIN OF ls_json,
  id TYPE string,
  name TYPE string,
  END OF ls_json.

DATA: lt_json LIKE STANDARD TABLE OF ls_json.

CLEAR ls_json.
ls_json-id = '001'.
ls_json-name = 'Stone'.

APPEND ls_json TO lt_json.

CLEAR ls_json.
ls_json-id = '002'.
ls_json-name = 'Brown'.

APPEND ls_json TO lt_json.

CREATE OBJECT serializer
    EXPORTING DATA = lt_json[].
CALL METHOD serializer->serialize( ).
lv_json = serializer->get_data( ).

WRITE / lv_json.

* Deserialze

WRITE /.
WRITE: / 'Deseriaze json string to internal table: '.

DATA: deserializer TYPE REF TO zcl_trex_json_deserializer.
CLEAR lt_json.

CREATE OBJECT deserializer.
CALL METHOD deserializer->deserialize(
  EXPORTING json = lv_json
  IMPORTING abap = lt_json[] ).

LOOP AT lt_json INTO ls_json.
  WRITE : / ls_json-id, ls_json-name.
ENDLOOP.

参考

How to deserialize an anonymous JSON array in abap?