WebSocket

Stateless roundtrips are fine for click-driven UIs, but some scenarios need the server to push — a news feed, a job-status indicator, a chat. abap2UI5 has no special API for this; you use SAP's standard WebSocket stack, and the frontend's z2ui5:Websocket control turns every message the channel delivers into an abap2UI5 event — no JavaScript in the app.

The building blocks:

Layer	Purpose
APC (Application Push Channel, SAPC)	Exposes the WebSocket endpoint over HTTP/S
AMC (Application Messaging Channel, SAMC)	In-system pub/sub — any ABAP code can broadcast into a channel
z2ui5:Websocket in the view	Opens the socket, hands every message to the backend as an event

Once both channels are configured, any COMMIT WORK that fires an AMC publish reaches every connected browser within milliseconds — no polling, no timer.

Server Side

An APC class extending cl_apc_wsp_ext_stateless_base binds an AMC consumer when a client connects, so AMC messages are forwarded to that socket. Broadcasting is then a one-liner from anywhere in the system:

DATA(lo_producer) = CAST if_amc_message_producer_text(
    cl_amc_channel_manager=>create_message_producer(
        i_application_id = `Z2UI5_SAMPLE`
        i_channel_id     = `/news_feed` ) ).
lo_producer->send( i_message = `New order arrived` ).

The APC handler class belongs to the APC application in SAPC; Z2UI5_CL_SMPS_APP_489_WS in the samples-stack repository is one, next to the consuming app listed below.

Client Side

The frontend ships the invisible custom control z2ui5:Websocket. It keeps the connection to the APC endpoint open across roundtrips; every text message the channel delivers lands in the bound value and fires received, which is an ordinary backend event. Sending is deliberately not part of the control — an app publishes from ABAP through AMC, as above — so consuming a push channel needs no JavaScript at all:

CLASS zcl_sample_websocket DEFINITION PUBLIC.

  PUBLIC SECTION.
    INTERFACES z2ui5_if_app.
    DATA mv_message  TYPE string.
    DATA mv_error    TYPE string.
    DATA mt_messages TYPE string_table.

  PROTECTED SECTION.
  PRIVATE SECTION.
ENDCLASS.

CLASS zcl_sample_websocket IMPLEMENTATION.
  METHOD z2ui5_if_app~main.

    IF client->check_on_navigated( ).

      DATA(view) = z2ui5_cl_ui5_view_builder=>factory(
          )->ele( n = `View` ns = `mvc`
              )->a( n = `xmlns`       v = `sap.m`
              )->a( n = `xmlns:mvc`   v = `sap.ui.core.mvc`
              )->a( n = `xmlns:z2ui5` v = `z2ui5.cc`

              )->ele( `Page`
                  )->a( n = `title` v = `News Feed`

                  )->tag( n = `Websocket` ns = `z2ui5`
                      )->a( n = `path`     v = `/sap/bc/apc/sap/z2ui5_sample`
                      )->a( n = `value`    v = client->_bind( mv_message )
                      )->a( n = `received` v = client->_event( `RECEIVED` )
                      )->a( n = `error`    v = client->_event( val   = `WS_ERROR`
                                                               t_arg = VALUE #( ( `${$parameters>/code}` )
                                                                                ( `${$parameters>/message}` ) ) )
                  )->tag( `MessageStrip`
                      )->a( n = `text`    v = client->_bind( mv_error )
                      )->a( n = `type`    v = `Error`
                      )->a( n = `visible` v = |\{= ${ client->_bind_path( mv_error ) } !== '' \}|
                  )->ele( `List`
                      )->a( n = `items` v = client->_bind( mt_messages )
                      )->ele( `items`
                          )->tag( `StandardListItem`
                              )->a( n = `title` v = `{TABLE_LINE}` ).

      client->view_display( view->stringify( ) ).

    ELSEIF client->check_on_event( `RECEIVED` ).
      INSERT mv_message INTO mt_messages INDEX 1.

    ELSEIF client->check_on_event( `WS_ERROR` ).
      mv_error = |Push channel { client->get_event_arg( 1 ) }: { client->get_event_arg( 2 ) }|.

    ENDIF.

  ENDMETHOD.
ENDCLASS.

The RECEIVED handler only changes bound data, so the view stays as it is and the list updates with the model — the connection is never touched by a roundtrip that leaves the view alone. A view_display( ) builds a new control, which opens a new connection.

Property
path	the APC path, resolved against the page's origin (/sap/bc/apc/sap/<application>); a full ws:// or wss:// URL is taken as it is
value	the text of the message currently reported to the backend
checkActive	false closes the connection; true again opens it — the way to pause a feed from ABAP. Default true
checkRepeat	false closes the connection after the first message. Default true

Event
received	one message arrived and value holds it
error	the connection could not be opened or was closed without the app asking; code is the WebSocket close code (1006 for a handshake that never completed — an inactive ICF node, a rejected logon, an unknown APC application) or CONSTRUCT when the browser refused the URL, message the text

Messages and errors are queued in the browser and handed over one per roundtrip, in the order they happened: a burst of messages while a roundtrip is in flight is not lost, and the queue holds 100 items before it drops new ones and logs it. After a connection the app did not close, the control reconnects with an increasing delay, from half a second up to thirty, and after five failed attempts in a row it stops until path or checkActive changes — each failure has fired error, so the backend heard about every one.

When to Reach For It

WebSockets cost a permanent connection per user — comparable to a stateful session in resource terms. Use them when push really matters:

• live dashboards, monitoring screens
• multi-user collaboration (chat, shared editing)
• long-running background jobs reporting status

For "refresh every few seconds" the Timer is cheaper and simpler.

WARNING

ABAP Push Channels and ABAP Messaging Channels exist from ABAP Platform 7.40 SP05 on. In ABAP Cloud (BTP ABAP Environment, S/4 Public Cloud) only the released APIs of the two are available — the samples-stack README says what its AMC/APC package needs from the system before you design around them.

Working Samples

Complete apps from the sample catalog that use what this page describes. Each is a single class in abap2UI5/samples unless its row names another of the three sample repositories — pull that repository with abapGit and start the class with ?app_start=<class>.

Sample	Class
Websocket — News Feed — connect, publish, list the active connections - no JavaScript	Z2UI5_CL_SMPS_APP_489 · samples-stack, branch 07-amc-apc