Overview
- In this blog, we try to consume a REST-Services in an OData-Service.
- Here we use GET operation of OData-Service
- and while consuming the REST-Service, we use HTTP-Method as POST to send request message and in acknowledgement REST-Service provides response which will be mapped to OData-Service's structure.
- This blogs is a business case example of parent blog:
Business Scenario:
- In a fiori-app, where data need to be accessed from a non-sap system.
- This non-sap system has a REST-Service technique for data exchange to out-side world.
- So, in fiori-App, we need an oData-Service which can consume/talk to non-sap's REST-Service for data Exchange.
- Note: Here we can consume REST-Services directly in fiori-App, but we recommend to access this via oData-Service, due to following reasons:
- The Cross-domain issue in JavaScript codes while accessing REST-Services when we deploy fiori-App in Fiori-Server.
REST Service Details:
- This REST-Service of non-sap system is a medium for data exchange between SAP-FioriApp and non-sap system
- REST (REpresenational State Transfer) is an architectural style that uses simple and lightweight mechanism for inter-machine communication.
- In this blog's example, this REST-Service has following components for data-exchange:
- EndPoint-URL:
- This consists of http(s), host, port and RestProjectPath of Non-SAP system
- For Example:
- Access-credentials:
- user-id and password which is required to access this REST service
- Request-Message:
- This is the input format which respective REST-Service understands, for which it runs its program logic and returns data accordingly.
- Here, below is the JASON input format:
[
{
"taskId":286079
},
{
"taskId":287571
}
]
- Response-Message:
- This is the output message format which we receive from REST-Service in acknowledgement.
- Here, output format is like:
{
"response":"Success",
"responseData":{
"response":"Posted successfully"
},
"error":null,
"errorList":[]
}
- EndPoint-URL:
- REST Services are working with ‘Resources’ instead of ‘Operations’
Steps to create oData Service [with GET_ENTITYSET]:
- To Consume above REST-Service, we implement oData-Service in following manner:
- Creation of an EntitySet which will have two Property:
- REQUEST
- To send JSON-Input in given REST-Service format
- RESPONSE
- To receive JSON-output from REST-Service.
- REQUEST
- Re-Definition of method 'GET_ENTITYSET' of respective Enity, where we write ABAP-Code to consume REST-Service.
- Creation of an EntitySet which will have two Property:
- Following detailed Steps can be followed for same:
[1] Create an EntityType and EntitySet
- To Create an OData-Serivice, go-to SAP-Firoi-Server t-code 'SEGW'
- Right click on Project's folder 'Entity Types' to create an Entity
- with Name 'ConsumeREST' with EntitySet name 'ConsumeRESTSet'
- Create two properties (REQUEST and RESPONSE) and make REQUEST as key.
- Save and 'Generate Runtime object’ by clicking circle icon (red/white) with project selection.
- Thus meta-structure for EntitySet gets created.
[2] Redefine method 'ConsumeRESTSet_GET_ENTITYSET'
- Next we need to re-define method 'GET_ENTITYSET' where abap-code will be written to consume REST service. This method will have following functionalities:
- Get input from property 'REQUEST' of ODataService's EntitySet 'ConsumeRESTSet'
- Consume/trigger REST-Service with this input
- In acknowledgement, REST-Service provide response, extract it and map it to oDataService's EntitySet 'ConsumeRESTSet' in property 'RESPONSE'
- To re-define same, go to Odata-Service project's folder 'Runtiime Artifacts' -> select 'DPC_EXT' class -> double click on it to go to abap runtime workbench
- Below is '_DPC_EXT' class, where we re-define 'GET_ENTITYSET'
- Go to folder '_DPC_EXT' -> folder 'Methods' -> folder 'Inherited Methods'
- select method 'ConsumeRESTSet_GET_ENTITYSET' -> right click -> select 'Redefine'
- Once method redefined, it get listed inside folder 'Methods/Redefinitions'
- and we write abap-code iside this method to do following tasks:
- To read input from property 'REQUEST' of ODataService's EntitySet 'ConsumeRESTSet'
- Call REST-Service by sending input and using its endpoint url
- In acknowledgement, REST-Service provide response,
- extract it and map it to oDataService's EntitySet 'ConsumeRESTSet' in property 'RESPONSE'
- Please note:
- We can not do it in redefinition of GET_ENTITY, because get_filter does not accessible inside it.
- Below is the screen of method 'ConsumeRESTSet_GET_ENTITYSET'
- And ABAP code written inside method 'ConsumeRESTSet_GET_ENTITYSET' is as follows:
method CONSUMERESTSET_GET_ENTITYSET.
DATA: lt_filters TYPE /iwbep/t_mgw_select_option,
ls_filter TYPE /iwbep/s_mgw_select_option,
ls_so TYPE /iwbep/s_cod_select_option,
LS_CONSUMERESTSET TYPE ZCL_ZTEST_ODATA_MPC=>TS_CONSUMEREST.
DATA: lv_RestSrvUrl TYPE STRING, "Var for Http REST Service Url
lv_HTTP_CLIENT TYPE REF TO IF_HTTP_CLIENT, "Var for Rest Http Client
LV_REQUEST TYPE STRING,
LV_RESPONSE TYPE STRING.
* Initiating filter to Read input from EnitySet of ODataService
lt_filters = io_tech_request_context->get_filter( )->get_filter_select_options( ).
* Extract input from Property 'REQUEST' of EntitySet 'CONSUMERESTSet'
Clear ls_filter.
READ TABLE lt_filters WITH TABLE KEY property = 'REQUEST' INTO ls_filter.
IF sy-subrc EQ 0.
READ TABLE ls_filter-select_options INTO ls_so index 1.
IF sy-subrc EQ 0.
LV_REQUEST = ls_so-low.
ENDIF.
ENDIF.
* REST Service URL
lv_RestSrvUrl = 'http://<ServiceIP>:<Port>/<REST_Service_Path>'.
*Steps to Call REST Service ===================================
*STEP-1 : CREATE HTTP CLIENT
CALL METHOD CL_HTTP_CLIENT=>CREATE_BY_URL
EXPORTING
URL = lv_RestSrvUrl
IMPORTING
CLIENT = lv_HTTP_CLIENT
EXCEPTIONS
ARGUMENT_NOT_FOUND = 1
PLUGIN_NOT_ACTIVE = 2
INTERNAL_ERROR = 3
OTHERS = 4
.
*STEP-2 : AUTHENTICATE HTTP CLIENT
CALL METHOD LV_HTTP_CLIENT->AUTHENTICATE
EXPORTING
USERNAME = 'Service_user-id'
PASSWORD = 'Service_password'.
*STEP-3 : Set headers for REST Service Request Call
CALL METHOD lv_HTTP_CLIENT->REQUEST->SET_HEADER_FIELD
EXPORTING NAME = '~request_method'
VALUE = 'POST'.
CALL METHOD lv_HTTP_CLIENT->REQUEST->SET_HEADER_FIELD
EXPORTING NAME = 'Content-Type'
VALUE = 'application/json; charset=utf-8'.
CALL METHOD lv_HTTP_CLIENT->REQUEST->SET_HEADER_FIELD
EXPORTING NAME = 'Accept'
VALUE = 'application/json, text/html'.
* STEP-3.1 : Attach Request Message
CALL METHOD LV_HTTP_CLIENT->REQUEST->SET_CDATA
EXPORTING DATA = LV_REQUEST
OFFSET = 0.
*STEP-4 : SEND HTTP REQUEST
CALL METHOD lv_HTTP_CLIENT->SEND
EXCEPTIONS
HTTP_COMMUNICATION_FAILURE = 1
HTTP_INVALID_STATE = 2.
*STEP-5 : GET HTTP RESPONSE
CALL METHOD lv_HTTP_CLIENT->RECEIVE
EXCEPTIONS
HTTP_COMMUNICATION_FAILURE = 1
HTTP_INVALID_STATE = 2
HTTP_PROCESSING_FAILED = 3.
*STEP-6 : Extract Rest-Service-Response
CLEAR LV_RESPONSE.
LV_RESPONSE = lv_HTTP_CLIENT->response->get_cdata( ).
*STEP-7 : Appending Rest-Service-Response to EntitySet of ODataService
CLEAR LS_CONSUMERESTSET.
LS_CONSUMERESTSET-REQUEST = LV_REQUEST. "Append Sent Request
LS_CONSUMERESTSET-RESPONSE = LV_RESPONSE. "Append Receievd Response
APPEND LS_CONSUMERESTSET TO ET_ENTITYSET.
CLEAR LS_CONSUMERESTSET.
endmethod.
- Save and activate this method.
[3] Testing OData-Service which consumes REST-Service
- Once above implementation gets completed, we can begin testing of service.
- Note: before testing make sure, odataService is already registered, for same you can refer below blog of mine:
- For testing in Fiori-server, go to t-code '/n/iwfnd/gw_client' and below oDataService uri will be used to invoke REST service via oData.
- here we are referring EntitySet 'ConsumeRESTSet'
- and in property 'REQUEST' we are passing JSON-Format input string which need to be send to REST-Service while calling
- This JSON-Input-String is REST-Service's input message format.
/sap/opu/odata/sap/ZTEST_ODATA_SRV/ConsumeRESTSet?$filter=REQUEST eq '[{"taskId":286079},{"taskId":287571}]'
- select Protocol 'HTTP'
- select HTTP Method 'GET', here please note we are passing input in uri
- Execute press 'F8' -> and in acknowledgement, we received REST-Service's output in Property 'RESPONSE'.
- for reference Here 'REQUEST' property has same data which we supplied as an input.
[4] Debugging OData-Service which consumes REST-Service
- Lets debug method 'ConsumeRESTSet_GET_ENTITYSET' to understand data flow.
- Set external breakpoints
- Execute/trigger oData Service from t-code '/n/iwfnd/gw_client'
- Debugger enters in method, see first we have extracted input from property 'REQUEST' of ODataService's EntitySet 'ConsumeRESTSet' into variable LV_REQUEST
- Next debugger stops post calling REST-Service, where we can understand with help of variable data 'LV_RESPONSE' which has extracted output from REST-Service acknowledgement
- The REST-Service's output present in variable 'LV_RESPONSE'. is been mapped/populated to oData-Service' EntitySet 'ConsumeRESTSet' with help of structure 'ET_ENTITYSET' as shown in below screen
- Thus we have understood how data is flowing from oDataService call to REST-Service call.
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