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AMC - ABAP Messaging Channels
ABAP messaging channels (AMC) are a method of communication between ABAP programs using messages. Using a publish-and-subscribe mechanism, messages can be exchanged between any AS ABAP programs, including communication between different user sessions and application services. Data objects with specific data types are allowed as messages. Messages that can be sent and received are:
ABAP messaging channels are implemented as repository objects that can be accessed in sender and receiver programs using an interface-based an class-based programming interface (API). The classes and interfaces of the API use the naming convention CL_AMC_... and IF_AMC_... respectively. . Communication between different application servers takes places across the message server.
The length of messages that can be sent is currently restricted to approximately 1 MB. Character strings are converted to the UTF-8 format. The limit can be increased by changing the profile parameter rdisp/long_messages/max_length.
Messaging Channels as Repository Objects
An ABAP messaging channel defined as a repository object must exist for each AMC communication. An ABAP messaging channel like this can be created in Repository Browser in ABAP Workbench by opening the context menu of a package and choosing Connectivity. Connectivity Browser in Object Navigator provides another means of access. To open Object Navigator for AMCs, use transaction SAMC.
An ABAP messaging channel is identified by its assignment to an application and by its name. The name must start with a forward slash character (/) and is not case-sensitive. The following properties can be defined for an ABAP messaging channel:
See the messaging channels /demo_text and /demo_binary of the application DEMO_AMC in the package SABAPDEMOS.
Sending AMC Messages
Before an AMC message can be sent in an authorized program (known as the publish part), the factory method CREATE_MESSAGE_PRODUCER of the system class CL_AMC_CHANNEL_MANAGER must be used to create a sender object for a messaging channel from the repository. The application and name of the channel are passed here. The returned reference variable of type IF_AMC_MESSAGE_PRODUCER must be cast to a type-specific interface that contains a method SEND used to send type-friendly messages. The following interfaces are possible, depending on the type of messaging channel used:
Objects of the class CL_AC_MESSAGE_TYPE_PCP, which implement the interface IF_AC_MESSAGE_TYPE_PCP, can be used to create messages for the Push Channel Protocol.
Receiving AMC Messages
Before an AMC message can be received in an authorized program (known as the subscribe part), the factory method CREATE_MESSAGE_PRODUCER of the system class CL_AMC_CHANNEL_MANAGER must be used to create a consumer for a messaging channel from the repository. The application and name of the channel are passed here. The returned reference variable has the type IF_AMC_MESSAGE_CONSUMER. The consumer methods START_MESSAGE_DELIVERY and STOP_MESSAGE_DELIVERY have two tasks:
Once one or more receiver objects have been registered, the statement WAIT FOR MESSAGING CHANNELS can be used to put the program in a wait state where it is ready to receive the messages. If, while the program is waiting, a message is received through a messaging channel for which a receiver object is registered, the associated RECEIVE method is executed and a check is made to see whether a logical condition is true or false. The wait state is persisted as long as the condition is false (but a maximum duration can be configured). In this way, multiple messages can be consumed until a message is received that ends the wait state.
Alongside the publish-and-subscribe mechanism, where the sender of message does not know the receivers, AMC also provides point-to-point communication, where a sender can create an AMC message for a specific receiver. The ID of the receiver session is required here.
The parameter I_COMMUNICATION_TYPE of the method CREATE_MESSAGE_PRODUCER_BY_ID can be used to configure whether a message is sent synchronously or asynchronously, with the latter the default. When a message is sent synchronously, the sender waits for confirmation that the message was passed to the receiver session. It raises an exception if this is not the case.
The executable example Receiving AMC Messages displays the ID of the receiver session. If this ID is entered in the example Sending AMC Messages, the message is sent synchronously and to this receiver session only.
Access to an ABAP messaging channel is controlled by specifying the authorized programs and their activities. When binding an APC WebSocket and when receiving using an APC WebSocket as a consumer, it is also possible to specify a virus scan profile to be used for the check performed by the virus scan interface (VSI).
AMC - Exceptions
Error situations in sender and receiver programs (such as violations of rules set by the properties of a messaging channel) raise exceptions of the class CX_AMC_ERROR.
AMC - Test and Analysis
AMC messages are both sent and received in AS ABAP, which means that existing test and analysis tools, such as ABAP Debugger, runtime analysis, or performance trace can be used as previously. There is also a special AMC logger:
The transaction SMAMC provides an overview of all ABAP messaging channels for which AMC consumers are registered.
Detailed information about AMC can be found in the ABAP Channels documentation in SAP Help Portal.