SAP 如何提供 RESTful Web 服务(3)

系列文章索引

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

解决 Rest 路径问题

本篇解决路径问题。

SICF 设置的是一个固定的路径，但 Rest 风格的 API 要求使用不同的路径和不同的 HTTP 请求来实现不同的操作。比如有一个学生的数据需要 CRUD:

列出所有学生 (GET)： /base-url/students，
创建新的学生 (POST): /base-rul/students/create
修改学生 (PUT)：/base-url/students/4
删除学生 (DELETE)：/base-url/students/6

根据 SAP Netweaver 的版本，可以使用 SAP 提供的标准 Rest 框架：cl_rest_http_handler 和 cl_rest_resource 来实现。如果版本比较早， SAP 中没有这两个类库的话，可以选择 DJ Adams 所写的 dispatcher 和 resource 类。DJ Adams的博客和 Github 上的源码请自行参考。

出于演示目的，本篇在处理方法 request_handler 方法中简单地实现根据浏览器提交的路径，进行不同的处理。

首先在 SAP 中创建一个 zemployee 表：

SAP 如何提供 RESTful Web 服务(3) - Rest 路径处理_第1张图片

然后使用事务码 SE24 新建一个类：ZCL_EMP_HANDLER，实现 IF_HTTP_EXTENSION 接口。在 handle_request 方法中写下面的处理代码：


METHOD if_http_extension~handle_request.

  DATA: lv_verb TYPE string,
        path TYPE string,
        path_info TYPE string,
        params TYPE string.

  DATA: lt_employee TYPE STANDARD TABLE OF zemployee,
        ls_employee LIKE LINE OF lt_employee.

  DATA: req_json TYPE string.

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

  DATA: result_tab TYPE match_result_tab ,
        wa         LIKE LINE OF result_tab.

  lv_verb = server->request->get_header_field( '~request_method' ) .
  path = server->request->get_header_field( '~request_uri' ).
  SPLIT path AT '?' INTO path_info params.

* POST http Method
* list all employees
  IF lv_verb = 'GET' AND path_info = '/zrest/employees'.
    SELECT * FROM zemployee INTO TABLE lt_employee.

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

    server->response->set_status( code = 200 reason = 'Ok' ).
    server->response->set_content_type( 'application/json' ).
    server->response->set_cdata( data = lv_json ).

  ENDIF.

* POST http method: create new employee
  IF lv_verb = 'POST' AND path_info = '/zrest/employees/create'.
    req_json = server->request->get_cdata( ).

    CLEAR ls_employee.
    CREATE OBJECT deserializer.
    CALL METHOD deserializer->deserialize(
      EXPORTING json = req_json
      IMPORTING abap = ls_employee ).

    MODIFY zemployee FROM ls_employee.

    server->response->set_status( code = 201 reason = 'Employee created successfully.' ).
  ENDIF.

* PUT http method: modify employee
  IF lv_verb = 'PUT'.
    REFRESH result_tab.
    FIND ALL OCCURRENCES OF REGEX '/zrest/employees/\d+' IN path_info RESULTS result_tab.

    IF NOT result_tab IS INITIAL.
      req_json = server->request->get_cdata( ).

      CLEAR ls_employee.
      CREATE OBJECT deserializer.
      CALL METHOD deserializer->deserialize(
        EXPORTING json = req_json
        IMPORTING abap = ls_employee ).

      MODIFY zemployee FROM ls_employee.

      server->response->set_status( code = 200 reason = 'Employee updated successfully.' ).
    ENDIF.
  ENDIF.

* DELETE http method: delete employee
  IF lv_verb = 'DELETE'.
    REFRESH result_tab.
    FIND ALL OCCURRENCES OF REGEX '/zrest/employees/\d+' IN path_info RESULTS result_tab.

    IF NOT result_tab IS INITIAL.
      DATA: f1 TYPE string,
            f2 TYPE string,
            f3 TYPE string,
            emp_id TYPE string.
      CLEAR wa.
      READ TABLE result_tab INTO wa INDEX 1.
      path_info = path_info+wa-offset(wa-length) .
      SPLIT path_info AT '/' INTO f1 f2 f3 emp_id.

      DELETE FROM zemployee WHERE empid = emp_id.

      server->response->set_status( code = 204 reason = 'Employee deleted successfully.' ).
    ENDIF.
  ENDIF.

ENDMETHOD.

代码比较直观，无需解释。因仅作为示例用途，未考虑严谨性，比如未考虑修改 employee 表时检查 empid 字段是否存在等。

完成之后通过 SICF 在 default_host 下面新建 zrest 子节点，提供对外的 web 服务。