Hyperledger fabric-sdk-java Basics Tutorial(转)

原文地址：Hyperledger fabric-sdk-java Basics Tutorial

https://hyperledger.org/) and would like to use fabric-sdk-java for their projects.

When learning a new technology I always try to search for some minimal working example I can get up and running in my environment. This is a starting point for me to further play around with APIs, debug and get better handle of the framework.

https://github.com/hyperledger/fabric-samples.git). What I have been missing is some minimal working project for Java developers using fabric-sdk-java. This tutorial tries to serve this purpose.

http://hyperledger-fabric.readthedocs.io/en/release/write_first_app.html .

https://github.com/hyperledger/fabric-samples.git to setup the network.

Tips:

fabric-samples/scripts/fabric-preload.sh script will download the docker images and tag them for you.
fabric-samples/fabcar/startFabric.sh can be used to start the fabcar network
In case you are experiencing issues you might want to do some docker cleanup

# !!! THIS WILL REMOVE ALL YOUR DOCKER CONTAINERS AND IMAGES !!!
# remove all containers
$ docker rm $(docker ps -qa)
# remove all mages
$ docker rmi --force $(docker images -qa)
# prune networks
$ docker network prune

Enough talking and let’s get something up and running….

Clone the example code from here into demo directory

git clone https://github.com/lkolisko/scratch.git tutorial

tutorial/hyperledger/fabric-sdk-java-scratch.

The project itself has just 4 three important files.

pom.xml —maven build file including dependency to fabric-sdk-java artifact. org.hyperledger.fabric-sdk-java: fabric-sdk-java:1.0.1 . There might be a new version available at the time you are reading this. You must ensure you fabric-sdk-java version is the same release series as the images used in fabric-samples. Otherwise you might run into incompatibility issues at protobuf leves or APIs.
src/main/java/lkolisko/hyperledger/example/AppUser.java — this is minimal implementation of the User interface. The sdk itself does not provide implementation, therefore we must do here ourselves.
src/main/java/lkolisko/hyperledger/example/HFJavaSDKBasicExample.java — this is the main class and will further talk about details bellow.
src/main/resources/log4j.xml — log4j configuration. I highly suggest to set the root logger to debug. You will be able to see all the information about communication between client the other components of the fabric network.

Enrolling admin

fabric-samples/fabcar/hfc-key-store and can be loaded) . But lets start from scratch and learn how to do that in Java.

CryptoSuite cryptoSuite = CryptoSuite.Factory.getCryptoSuite();
HFCAClient caClient = HFCAClient.createNewInstance(“grpc://localhost:7054”, null);
caClient.setCryptoSuite(cryptoSuite);

grpc://localhost:7054 is the endpoint where fabric-ca server listens. You can check that running docker ps . The properties can be left empty or null for now.

Enroll Admin

To communicate with fabric components we have to have key pair and a certificate signed by the fabric-ca. We can either use the crypto material generated in fabric-samples/fabcar/hfc-key-store. For the purpose of learning the API we will let the fabric-ca client generate the crypto material for us.

Enrollment adminEnrollment = caClient.enroll("admin", "adminpw");
AppUser admin = new AppUser("admin","org1", "Org1MSP", adminEnrollment);

The ca client will generate the key pair and CSR (certificate signature request) using the CryptoSuite and send it to the fabric-ca.

fabri-ca will

authenticate admin using basic authentication
perform verification e.g. check if max enrollment count for the account has not been reached
sign the certificate
store the certificate (along with its serial number, aki and other information)
send it back to client

The Enrollment object contains private key and the certificate. The sample stores the object using Java Serialization. This is definitely a bad practice and is used just for the purpose of keeping the example simple.

Register and Enroll user

In the step two we are going to register a new user and enroll the user.

RegistrationRequest rr = new RegistrationRequest("hfuser", "org1");
String userSecret = caClient.register(rr, registrar);
Enrollment userEnrollment = caClient.enroll("hfuser", userSecret);
AppUser appUser = new AppUser("hfuser", "org1","Org1MSP", userEnrollment);

http://hyperledger-fabric-ca.readthedocs.io/en/latest/users-guide.html .

RegistrationRequest we will call fabri-ca using registrar (admin) . The fabric-ca will answer with secret (password) we will use for enrollment of the user. This is the same as we did for the admin in the previous step.

At this moment we have admin — private key and signed certificate and user with private key and signed certificate. This opens as the door to talk to fabric itself.

Initialize HF Client

We will create client instance using HFClient factory and set the default crypto suite. Next we set use context. This will be the account under which we are going to talk to Hyperledger Fabric and its private key will be used to sign the request.

CryptoSuite cryptoSuite = CryptoSuite.Factory.getCryptoSuite();
HFClient client = HFClient.createNewInstance();
client.setCryptoSuite(cryptoSuite);
client.setUserContext(appUser);

Initialize Channel object

channel.initialize() we are ready to go.

Peer peer = client.newPeer("peer", "grpc://localhost:7051"); EventHub eventHub = client.newEventHub("eventhub", "grpc://localhost:7053");
Orderer orderer = client.newOrderer("orderer", "grpc://localhost:7050");
Channel channel = client.newChannel("mychannel");
channel.addPeer(peer);
channel.addEventHub(eventHub);
channel.addOrderer(orderer);
channel.initialize();

Invoking chain code

setVersion.

QueryByChaincodeRequest qpr = client.newQueryProposalRequest();
ChaincodeID fabcarCCId = ChaincodeID.newBuilder().setName("fabcar").build();
qpr.setChaincodeID(fabcarCCId);
qpr.setFcn("queryAllCars");
Collection<ProposalResponse> res = channel.queryByChaincode(qpr);
for (ProposalResponse pres : res) {
    String stringResponse = new    String(pres.getChaincodeActionResponsePayload());
    log.info(stringResponse);
}

Once we are set, let submit the query request and enjoy the response. The response is protobuf backed object, therefore we just rely on simple toString here for simplicity.

Please do not consider the code above as a best practice to follow. We are ignoring handling invalid responses, exceptions, storing credentials using serialization and dozen of other bad practices. The purpose of the sample is to get something working with minimal effort and get you on track.

To study further I highly recommend checking

https://github.com/hyperledger/fabric-sdk-java/blob/master/src/test/java/org/hyperledger/fabric/sdkintegration/End2endIT.java
https://github.com/hyperledger/fabric-sdk-java/blob/master/src/test/java/org/hyperledger/fabric/sdkintegration/NetworkConfigIT.java .

Happy coding !

— Lukas