Hyperledger Java SDK Client Event Listener

Question

I have a Java SDK based client for the Hyperledger fabric and am able to connect and send transaction proposal requests, create entries in the ledger and query the ledger.

I am struggling with registering and listening to BLOCK and CHAINCODE events. I want to start a separate thread on the client that is dedicated to listening and processing these events.

What I found so far:

HFClient client = HFClient.createNewInstance();
Channel channel = client.newChannel("channel01");
EventHub eventHub = client.newEventHub("eh01", "grpc://abc.xyz.us:7053");
channel.addEventHub(eventHub);

Beyond this I am lost. Can someone please post a sample of how to do this?

score 5 · Answer 1 · answered May 09 '18 at 11:11

once you add the eventhub, you need to register the lister for this event. Please see the example below.

        BlockListener blockListener = new BlockListener() {         
        @Override
        public void received(BlockEvent arg0) {
            Block block = arg0.getBlock();

            System.out.println("BLock All FIelds :" + block.getAllFields());
            System.out.println("BLock Number :" + arg0.getBlockNumber());               

            System.out.println("THis is buyer Listener..");
        }
    };

    channel.registerBlockListener(blockListener);

Whatever you will will write in the received method will get called whenever the block is added to the blockchain. Hope this would help you.

thanks for this example. how can I then handle chaincode events that are added to each transaction in a block? — a.hrdie, Jun 15 '18 at 13:09

score 0 · Answer 2 · answered Feb 11 '19 at 21:05

For transaction events you need another listener:

String chaincodeEventListenerHandle = channel.registerChaincodeEventListener(
                    Pattern.compile(".*"), Pattern.compile(Pattern.quote(EXPECTED_EVENT_NAME)),
                    (handle, blockEvent, chaincodeEvent) -> {
                        final String es = blockEvent.getPeer() != null
                                ? blockEvent.getPeer().getName()
                                : blockEvent.getEventHub().getName();
                        System.out.format(
                                "Chaincode event with handle: %s"
                                + ", thread name: %s"
                                + ", chaincode Id: %s"
                                + ", chaincode event name: %s"
                                + ", transaction id: %s"
                                + ", event payload: \"%s\""
                                + ", from eventhub: %s\n",
                                Thread.currentThread().getName(),
                                handle, 
                                chaincodeEvent.getChaincodeId(),
                                chaincodeEvent.getEventName(), 
                                chaincodeEvent.getTxId(),
                                new String(chaincodeEvent.getPayload()),
                                es);

                    });

...

 channel.unregisterChaincodeEventListener(chaincodeEventListenerHandle);

Hyperledger Java SDK Client Event Listener

2 Answers2