Hyperledger Fabric Gateway client API for Java
The Fabric Gateway SDK allows applications to interact with a Fabric blockchain network. It provides a simple API to submit transactions to a ledger or query the contents of a ledger with minimal code. The Gateway SDK implements the Fabric programming model as described in the Developing Applications chapter of the Fabric documentation.
Client applications interact with the blockchain network using a Fabric Gateway. A session for a given client
identity is established by building and connecting to a Fabric Gateway using a gRPC connection to the Gateway
endpoint, client identity, and client signing implementation. The returned Gateway enables interaction
with any of the blockchain Networks (channels) accessible through the Fabric Gateway. This in turn
provides access to Smart Contracts within chaincode deployed to that blockchain network, and to which
transactions can be submitted or queries can be evaluated.
gRPC connections to a Fabric Gateway may be shared by all Gateway instances interacting with that
Fabric Gateway.
The following shows a complete code sample of how to connect to a fabric network, submit a transaction and query the ledger state using an instantiated smart contract.
import io.grpc.Grpc;
import io.grpc.ManagedChannel;
import io.grpc.TlsChannelCredentials;
import org.hyperledger.fabric.client.*;
import org.hyperledger.fabric.client.identity.*;
public static void main(final String[] args) throws CommitException, GatewayException, InterruptedException {
Reader certReader = Files.newBufferedReader(certificatePath);
X509Certificate certificate = Identities.readX509Certificate(certReader);
Identity identity = new X509Identity("mspId", certificate);
Reader keyReader = Files.newBufferedReader(privateKeyPath);
PrivateKey privateKey = Identities.readPrivateKey(keyReader);
Signer signer = Signers.newPrivateKeySigner(privateKey);
ManagedChannel grpcChannel = Grpc.newChannelBuilder("gateway.example.org:1337", TlsChannelCredentials.create())
.build();
Gateway.Builder builder = Gateway.newInstance()
.identity(identity)
.signer(signer)
.connection(grpcChannel);
try (Gateway gateway = builder.connect()) {
Network network = gateway.getNetwork("channelName");
Contract contract = network.getContract("chaincodeName");
byte[] putResult = contract.submitTransaction("put", "time", LocalDateTime.now().toString());
System.out.println(new String(putResult, StandardCharsets.UTF_8));
byte[] getResult = contract.evaluateTransaction("get", "time");
System.out.println(new String(getResult, StandardCharsets.UTF_8));
} finally {
grpcChannel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
}
}