SAP ABAP和Java跨域请求问题的解决方案

There is an excellent blog Cross-domain communications with ABAP and JSONP written by Alessandro Spadoni.
And in this blog, I just record down my own study experience about how to achieve cross domain request in ABAP and Java.

Cross Domain Request in ABAP

Create a new ICF node in tcode SICF, implement the following source code in its handler class.4

METHOD if_http_extension~handle_request.
   DATA: lv_text TYPE string value 'hello world'.
   server->response->append_cdata(
                        data   = lv_text
                        length = strlen( lv_text ) ).
  ENDMETHOD.

Access the url in browser, and it works as expected.

And now try to access the url by AJAX in jQuery:

function getPostByAJAX(requestURL){
   var html = $.ajax({
      url: requestURL,
      async: false}).responseText; 
   debugger;
   return html;
}

You will get the following error message in browser: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘null’ is therefore not allowed access.

The request fails to finish due to same origin policy.

One remedy is to use Cross-Origin Resource Sharing.

Add a few more codes in the ICF handler class:

  METHOD if_http_extension~handle_request.

    DATA: lv_text TYPE string VALUE 'hello world'.
    CONSTANTS: cv_white_id TYPE string VALUE 'i042416'.

    DATA(lv_origin) = server->request->get_header_field( 'origin' ).
    DATA(lv_userid) = server->request->get_form_field( 'userId' ).
    IF lv_userid = cv_white_id.
      server->response->set_header_field(
         EXPORTING
           name  = 'Access-Control-Allow-Origin'
           value = lv_origin ).
    ENDIF.
    server->response->append_cdata(
                         data   = lv_text
                         length = strlen( lv_text ) ).
  ENDMETHOD.

And when requesting the resource again but this time with a hard coded user id which acts a a simulation of white list, the request can be successfully processed this time thanks to CORS:

The response is available in JavaScript code:

Change the user id to any other one and the request will fail again:

Cross Domain Request in Java

The similar logic as in ABAP.
Create a dynamic web project in Java with a servlet named “HelloWorldServlet”:

Copy the following implementation source code into the Servlet:

public class HelloWorldServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public HelloWorldServlet() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {    
        List allowedUserId = Arrays.asList(getServletContext().getInitParameter("userIds").trim().split(","));
        String clientOrigin = request.getHeader("origin");
        String ipAddress = request.getHeader("x-forwarded-for");
        if (ipAddress == null) {
            ipAddress = request.getRemoteAddr();
        }
        String userId = request.getParameter("userId");
        if( userId != null)
            userId = userId.trim();
        if( allowedUserId.contains(userId)){
            response.setHeader("Access-Control-Allow-Origin", clientOrigin);
        }
        if( ipAddress.equals("0:0:0:0:0:0:0:1"))
            response.getWriter().println("local one");
        else
            response.getWriter().println("Hello World!");
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

The web.xml in folder WEB-INF, which the allowed user ids are listed in node .

    JerryTest
    
        Hello
        index.html
    
    
        userIds
        i042416,i042417,i042418
    
    
        
        HelloWorldServlet
        HelloWorldServlet
        helloworld.HelloWorldServlet
    
    
        
        HelloWorldServlet
        /Hello
    

Now access the servlet with user id which is not included in the list, and the request fails:

And perform positive test via an allowed user id specified in request:

Request is successfully handled and returned to browser:

Client side workaround

Sometimes for development purpose we would like to bypass the limitation of same origin policy, and here below are two approaches I used in my daily work.

workaround 1: use Chrome extension “Allow-Control-Allow-Origin”

Once installed, just switch on CORS via checkbox:

This extension will automatically add a new field in request header to do the magic:

Now the response is available with the help of this extension, even the requested user id is not in allowed list:

workaround 2: disable same origin policy via Chrome start command argument –disable-web-security

Create a new shortcut and add the argument –disable-web-security

request detail:

This time the request is still successfully handled – you will see a warning “Stability and security will suffer.” in Chrome.

要获取更多Jerry的原创文章，请关注公众号"汪子熙":