The Send Mediator is used to send messages out of Synapse to an endpoint. The Send Mediator also copies any message context properties from the current message context to the reply message received on the execution of the send operation, so that the response could be correlated back to the request. Messages may be correlated by WS-A MessageID, or even simple custom text labels.
A send operation can be blocking or non-blocking depending on the actual transport implementation used. The default NIO-based http/s implementation does not block on a send. Therefore, if a message should be sent and further processed (e.g. transformed) afterwards, it is required to clone the message into two copies and then perform the processing to avoid conflicts.
The Send mediator is a content-unaware mediator.
Do not add any mediator configurations after Send mediator in the same sequence, because WSO2 ESB does not process them. Any mediator configuration after the Send mediator should go to the outSequence or receive sequence.
If the message is to be sent to one or more endpoints, use the following syntax.
endpointreftoken refers to the following:
endpointtoken refers to an anonymous endpoint definition.
|Select Endpoint Type|
This parameter is used to specify the endpoint type to which the message should be sent. The available options are as follows.
|Receiving Sequence Type|
The sequence to use for handling the response from the endpoint. Possible options are as follows.
|Build Message Before Sending|
This parameter is used to specify whether the message should be built before sending or not. The possible values are as follows.
Example 1 - Send mediator used in the In sequence and Out sequence
In this example, the first send operation is included in the In mediator. Both the request and response will go through the main sequence, but only request messages will go through the In mediator. Similarly, only response messages will go through the Out mediator. The request will be forwarded to the endpoint with the given address. The response will go through the second send operation, which in this example just sends it back to the client because there is no Out endpoint specified.
Example 2 - Specifying a response handling sequence (service chaining)
In this example, requests are sent to the
PersonInfoEpr endpoint, and responses from the service at that endpoint are handled by a sequence named personInfoSeq. This approach is particularly useful for service chaining. For example, if you want to take the responses from the
PersonInfoEpr service and send them to the
CreditEpr service for additional processing before sending the final response back to the client. In this case, you can configure the
personInfoSeq sequence to send the response to the
CreditEpr service and also specify another receive sequence named
creditSeq that sends the response from the
CreditEpr service back to the client. Following is the configuration of these sequences.
Example 3 - Configuring a blocking/non-blocking send operation
In this example, the Send mediator in a proxy service using the VFS transport is transferring a file to a VFS endpoint. VFS is a non-blocking transport by default, which means a new thread is spawned for each outgoing message. The Property mediator added before the Send mediator removes the ClientAPINonBlocking property from the message to perform the mediation in a single thread. This is required when the file being transferred is large and you want to avoid out-of-memory failures.