Require explanation for the responder flows

[waynelcw]

The following lines can be seen in many other flows.
But it is hard to follow by just viewing the code.

accounts-demo-supplychain/workflows/src/main/kotlin/com/accounts_SupplyChain/flows/SendInvoice.kt

Lines 105 to 128 in d4cac71

	val accountMovedTo = AtomicReference<AccountInfo>()
	//extract account information from transaction
	val transactionSigner = object : SignTransactionFlow(counterpartySession) {
	override fun checkTransaction(tx: SignedTransaction) {
	val keyStateMovedTo = tx.coreTransaction.outRefsOfType(InvoiceState::class.java).first().state.data.recipient
	keyStateMovedTo?.let {
	accountMovedTo.set(accountService.accountInfo(keyStateMovedTo.owningKey)?.state?.data)
	}
	if (accountMovedTo.get() == null) {
	throw IllegalStateException("Account to move to was not found on this node")
	}
	}
	}
	//record and finalize transaction
	val transaction = subFlow(transactionSigner)
	if (counterpartySession.counterparty != serviceHub.myInfo.legalIdentities.first()) {
	val recievedTx = subFlow(ReceiveFinalityFlow(counterpartySession, expectedTxId = transaction.id, statesToRecord = StatesToRecord.ALL_VISIBLE))
	val accountInfo = accountMovedTo.get()
	if (accountInfo != null) {
	subFlow(BroadcastToCarbonCopyReceiversFlow(accountInfo, recievedTx.coreTransaction.outRefsOfType(InvoiceState::class.java).first()))
	}
	}
	}