interface FlowExternalOperation represents an external process that blocks a flow from continuing until the result of
has been retrieved. Examples of external processes where
interface FlowExternalOperation would be useful include, triggering a long running
process on an external system or retrieving information from a service that might be down.
The flow will suspend while it is blocked to free up a flow worker thread, which allows other flows to continue processing while waiting for the result of this process.
interface FlowExternalOperation should ideally hold references to any external values required by
FlowExternalOperation.execute. These references
should be passed into the implementation's constructor. For example, an amount or a reference to a Corda Service could be passed in.
It is discouraged to insert into the node's database from a
interface FlowExternalOperation, except for keeping track of deduplicationIds that
have been processed. It is possible to interact with the database from inside a
interface FlowExternalOperation but, for most operations, is not
R execute(java.lang.String deduplicationId)
Executes a blocking operation.
deduplicationId - If the flow restarts from a checkpoint (due to node restart, or via a visit to the flow
hospital following an error) the execute method might be called more than once by the Corda flow state machine.
For each duplicate call, the deduplicationId is guaranteed to be the same allowing duplicate requests to be
de-duplicated if necessary inside the execute method.