# Hyperledger Fabric Gateway SDK for Java

The Fabric Gateway SDK allows applications to interact with a Fabric blockchain network.

请参阅: 说明

程序包
程序包 | 说明
--- | ---
org.hyperledger.fabric.gateway | This package provides the set of interfaces that enable a Java application to interact with a Fabric blockchain network.
org.hyperledger.fabric.gateway.spi | This package provides the set of interfaces that enable a Java developer to extend the set of built in handlers for controlling gateway strategies.

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.

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 (fabcar sample).

        public static void main(String[] args) throws IOException {
            // Load an existing wallet holding identities used to access the network.
            Path walletDirectory = Paths.get("wallet");
            Wallet wallet = Wallets.newFileSystemWallet(walletDirectory);

            // Path to a common connection profile describing the network.
            Path networkConfigFile = Paths.get("connection.json");

            // Configure the gateway connection used to access the network.
            Gateway.Builder builder = Gateway.createBuilder()
                    .identity(wallet, "user1")
                    .networkConfig(networkConfigFile);

            // Create a gateway connection
            try (Gateway gateway = builder.connect()) {

                // Obtain a smart contract deployed on the network.
                Network network = gateway.getNetwork("mychannel");
                Contract contract = network.getContract("fabcar");

                // Submit transactions that store state to the ledger.
                byte[] createCarResult = contract.createTransaction("createCar")
                        .submit("CAR10", "VW", "Polo", "Grey", "Mary");
                System.out.println(new String(createCarResult, StandardCharsets.UTF_8));

                // Evaluate transactions that query state from the ledger.
                byte[] queryAllCarsResult = contract.evaluateTransaction("queryAllCars");
                System.out.println(new String(queryAllCarsResult, StandardCharsets.UTF_8));

            } catch (ContractException | TimeoutException | InterruptedException e) {
                e.printStackTrace();
            }
        }

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