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<String> 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 <context-param>.

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://java.sun.com/xml/ns/javaee"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"    id="WebApp_ID" version="2.5">    <display-name>JerryTest</display-name>    <welcome-file-list>        <welcome-file>Hello</welcome-file>        <welcome-file>index.html</welcome-file>    </welcome-file-list>    <context-param>        <param-name>userIds</param-name>        <param-value>i042416,i042417,i042418</param-value>    </context-param>    <servlet>        <description></description>        <display-name>HelloWorldServlet</display-name>        <servlet-name>HelloWorldServlet</servlet-name>        <servlet-class>helloworld.HelloWorldServlet</servlet-class>    </servlet>    <servlet-mapping>        <!-- http://stackoverflow.com/questions/4140448/difference-between-and-in-servlet-mapping-url-pattern -->        <servlet-name>HelloWorldServlet</servlet-name>        <url-pattern>/Hello</url-pattern>    </servlet-mapping></web-app>

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.

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