You might want to monitor the blockchain to take action when a transaction impacts your account. the good news is that what we have learned until now is sufficient to implement this!
The complete script is available at code/05/groovy-monitoring.groovy.
We define the endpoint connection as earlier, then define the address we want to monitor:
monitored_address=Address.fromEncoded("TCJMM2-MN62XC-Y4TREH-ACOJ3M-2FOEC2-MUKCSX-XVR6".replaceAll("-",""))
We need to remote the - in the address for easy comparison later.
What we will do is getting the last block every 3 seconds, and if we get a block we didn't see earlier, we'll
check the transactions to see if these impact our account.
To determine if we receive a new block, we check if its height (block.getHeight()) is higher than what we have seen earlier.
FIXME: is it possible that we switch to another fork of the chain and miss blocks?
Getting the transactions of a block is easy with block.getTransactions(). However in this script we only want to
check transfers, so we check the transaction type: if (t.getType()==TransactionTypes.TRANSFER).
When we see a transfer transaction in a block, we look at the accounts it impacts (t.getAccounts()) and if our
monitored address matches one of these accounts (a.getAddress()), we examine and possibly print out information like the transaction recipient
(t.getRecipient()), the debtor who pays the fee (t.getDebtor()), the signer (t.getSigner()), and the message (t.getMessage()).
The messages is an arrya of bytes, that we can reassemble in a string with new String(t.getMessage().getDecodedPayload(),"UTF-8").
The hash of the transaction is computed with HashUtils.calculateHash(t).