Use Executor in asset-transfer-events/application-gateway-java

The default ForkJoinPool.commonPool may have limited capacity in some environments, risking deadlock. This implementation also better demonstrates handling of connection errors.

Signed-off-by: Mark S. Lewis <Mark.S.Lewis@outlook.com>

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

@@ -7,29 +7,33 @@
 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.Network;
 import org.hyperledger.fabric.client.SubmitException;
 
 import java.nio.charset.StandardCharsets;
 import java.time.Instant;
-import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
-public final class App {
+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();
@@ -42,8 +46,8 @@ public static void main(final String[] args) throws Exception {
 				.submitOptions(options -> options.withDeadlineAfter(5, TimeUnit.SECONDS))
 				.commitStatusOptions(options -> options.withDeadlineAfter(1, TimeUnit.MINUTES));
 
-		try (var gateway = builder.connect()) {
-			new App(gateway).run();
+		try (var gateway = builder.connect(); var app = new App(gateway)) {
+			app.run();
 		} finally {
 			grpcChannel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
 		}
@@ -71,15 +75,22 @@ private CloseableIterator<ChaincodeEvent> startChaincodeEventListening() {
 		System.out.println("\n*** Start chaincode event listening");
 
 		var eventIter = network.getChaincodeEvents(chaincodeName);
+		executor.execute(() -> readEvents(eventIter));
 
-		CompletableFuture.runAsync(() -> {
+		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);
 			});
-		});
-
-		return eventIter;
+		} catch (GatewayRuntimeException e) {
+			if (e.getStatus().getCode() != Status.Code.CANCELLED) {
+				throw e;
+			}
+		}
 	}
 
 	private String prettyJson(final byte[] json) {
@@ -154,4 +165,9 @@ private void replayChaincodeEvents(final long startBlock) {
 			}
 		}
 	}
+
+	@Override
+	public void close() throws Exception {
+		executor.shutdownNow();
+	}
 }