The Drop Mediator stops the processing of the current message. This mediator is useful for ensuring that the message is sent only once and then dropped by the ESB. If you have any mediators defined after the <drop/> element, they will not be executed, because <drop/> is considered to be the end of the message flow.
When the Drop mediator is within the "in" sequence, it sends an HTTP 202 Accepted response to the client when it stops the message flow. When the Drop mediator is within the "out" sequence before the Send mediator, no response is sent to the client.
Syntax
The drop token refers to a <drop> element, which is used to stop further processing of a message:
<drop/>
UI Configuration
As with other mediators, after adding the drop mediator to a sequence, you can click its up and down arrows to move its location in the sequence.
Example
<definitions xmlns="http://ws.apache.org/ns/synapse">
<filter source="get-property('To')" regex=".*/StockQuote.*">
<send>
<endpoint>
<address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
</endpoint>
</send>
<drop/>
</filter>
<send/>
</definitions>
In this scenario, the message is dropped after it is sent to the endpoint. This will prevent the message from being sent twice from the in-path.
You can also use the drop mediator for messages that do not meet the filter criteria in case the client is waiting for a response to ensure the message was received by the ESB. For example:
<definitions xmlns="http://ws.apache.org/ns/synapse">
<sequence name="main">
<in>
<!-- filtering of messages with XPath and regex matches -->
<filter source="get-property('To')" regex=".*/StockQuote.*">
<then>
<send>
<endpoint>
<address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
</endpoint>
</send>
</then>
<else>
<drop/>
</else>
</filter>
...
In this scenario, if the message doesn't meet the filter condition, it is dropped, and the HTTP 202 Accepted response is sent to the client. If you did not include the drop mediator, the client would not receive any response.