fabric-samples/asset-transfer-events/application-gateway-java/src/main/java/App.java

/*
 * Copyright IBM Corp. All Rights Reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonParser;
import io.grpc.Status;
import org.hyperledger.fabric.client.ChaincodeEvent;
import org.hyperledger.fabric.client.CloseableIterator;
import org.hyperledger.fabric.client.CommitException;
import org.hyperledger.fabric.client.CommitStatusException;
import org.hyperledger.fabric.client.Contract;
import org.hyperledger.fabric.client.EndorseException;
import org.hyperledger.fabric.client.Gateway;
import org.hyperledger.fabric.client.GatewayRuntimeException;
import org.hyperledger.fabric.client.Hash;
import org.hyperledger.fabric.client.Network;
import org.hyperledger.fabric.client.SubmitException;

import java.nio.charset.StandardCharsets;
import java.time.Instant;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public final class App implements AutoCloseable {
    private static final String channelName = "mychannel";
    private static final String chaincodeName = "events";

    private final Network network;
    private final Contract contract;
    private final String assetId = "asset" + Instant.now().toEpochMilli();
    private final Gson gson = new GsonBuilder().setPrettyPrinting().create();
    private final ExecutorService executor = Executors.newCachedThreadPool();

    public static void main(final String[] args) throws Exception {
        var grpcChannel = Connections.newGrpcConnection();
        var builder = Gateway.newInstance()
                .identity(Connections.newIdentity())
                .signer(Connections.newSigner())
                .hash(Hash.SHA256)
                .connection(grpcChannel)
                .evaluateOptions(options -> options.withDeadlineAfter(5, TimeUnit.SECONDS))
                .endorseOptions(options -> options.withDeadlineAfter(15, TimeUnit.SECONDS))
                .submitOptions(options -> options.withDeadlineAfter(5, TimeUnit.SECONDS))
                .commitStatusOptions(options -> options.withDeadlineAfter(1, TimeUnit.MINUTES));

        try (var gateway = builder.connect(); var app = new App(gateway)) {
            app.run();
        } finally {
            grpcChannel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
        }
    }

    public App(final Gateway gateway) {
        network = gateway.getNetwork(channelName);
        contract = network.getContract(chaincodeName);
    }

    public void run() throws EndorseException, SubmitException, CommitStatusException, CommitException {
        // Listen for events emitted by subsequent transactions, stopping when the try-with-resources block exits
        try (var eventSession = startChaincodeEventListening()) {
            var firstBlockNumber = createAsset();
            updateAsset();
            transferAsset();
            deleteAsset();

            // Replay events from the block containing the first transaction
            replayChaincodeEvents(firstBlockNumber);
        }
    }

    private CloseableIterator<ChaincodeEvent> startChaincodeEventListening() {
        System.out.println("\n*** Start chaincode event listening");

        var eventIter = network.getChaincodeEvents(chaincodeName);
        executor.execute(() -> readEvents(eventIter));

        return eventIter;
    }

    private void readEvents(final CloseableIterator<ChaincodeEvent> eventIter) {
        try {
            eventIter.forEachRemaining(event -> {
                var payload = prettyJson(event.getPayload());
                System.out.println("\n<-- Chaincode event received: " + event.getEventName() + " - " + payload);
            });
        } catch (GatewayRuntimeException e) {
            if (e.getStatus().getCode() != Status.Code.CANCELLED) {
                throw e;
            }
        }
    }

    private String prettyJson(final byte[] json) {
        return prettyJson(new String(json, StandardCharsets.UTF_8));
    }

    private String prettyJson(final String json) {
        var parsedJson = JsonParser.parseString(json);
        return gson.toJson(parsedJson);
    }

    private long createAsset() throws EndorseException, SubmitException, CommitStatusException {
        System.out.println("\n--> Submit transaction: CreateAsset, " + assetId + " owned by Sam with appraised value 100");

        var commit = contract.newProposal("CreateAsset")
                .addArguments(assetId, "blue", "10", "Sam", "100")
                .build()
                .endorse()
                .submitAsync();

        var status = commit.getStatus();
        if (!status.isSuccessful()) {
            throw new RuntimeException("failed to commit transaction with status code " + status.getCode());
        }

        System.out.println("\n*** CreateAsset committed successfully");

        return status.getBlockNumber();
    }

    private void updateAsset() throws EndorseException, SubmitException, CommitStatusException, CommitException {
        System.out.println("\n--> Submit transaction: UpdateAsset, " + assetId + " update appraised value to 200");

        contract.submitTransaction("UpdateAsset", assetId, "blue", "10", "Sam", "200");

        System.out.println("\n*** UpdateAsset committed successfully");
    }

    private void transferAsset() throws EndorseException, SubmitException, CommitStatusException, CommitException {
        System.out.println("\n--> Submit transaction: TransferAsset, " + assetId + " to Mary");

        contract.submitTransaction("TransferAsset", assetId, "Mary");

        System.out.println("\n*** TransferAsset committed successfully");
    }

    private void deleteAsset() throws EndorseException, SubmitException, CommitStatusException, CommitException {
        System.out.println("\n--> Submit transaction: DeleteAsset, " + assetId);

        contract.submitTransaction("DeleteAsset", assetId);

        System.out.println("\n*** DeleteAsset committed successfully");
    }

    private void replayChaincodeEvents(final long startBlock) {
        System.out.println("\n*** Start chaincode event replay");

        var request = network.newChaincodeEventsRequest(chaincodeName)
                .startBlock(startBlock)
                .build();

        try (var eventIter = request.getEvents()) {
            while (eventIter.hasNext()) {
                var event = eventIter.next();
                var payload = prettyJson(event.getPayload());
                System.out.println("\n<-- Chaincode event replayed: " + event.getEventName() + " - " + payload);

                if (event.getEventName().equals("DeleteAsset")) {
                    // Reached the last submitted transaction so break to close the iterator and stop listening for events
                    break;
                }
            }
        }
    }

    @Override
    public void close() {
        executor.shutdownNow();
    }
}