环境准备

JDK（8u131以上）

corda训练营

代码地址：

https://github.com/corda/bootcamp-cordapp

个人gitee项目：https://gitee.com/zheshiyigegexingwangzhan/bootcamp-cordapp.git

添加国内镜像

当前项目修改

下载代码之后为了更快的下载依赖，添加国内的镜像：

maven { url 'http://maven.aliyun.com/nexus/content/groups/public/'}

直接修改全局的gradle配置

在~/.gradle目录下新建init.gradle文件，写入以下内容：

allprojects{
    repositories {
        def ALIYUN_REPOSITORY_URL = 'http://maven.aliyun.com/nexus/content/groups/public'
        def ALIYUN_JCENTER_URL = 'http://maven.aliyun.com/nexus/content/repositories/jcenter'
        all { ArtifactRepository repo ->
            if(repo instanceof MavenArtifactRepository){
                def url = repo.url.toString()
                if (url.startsWith('https://repo1.maven.org/maven2')) {
                    project.logger.lifecycle "Repository ${repo.url} replaced by $ALIYUN_REPOSITORY_URL."
                    remove repo
                }
                if (url.startsWith('https://jcenter.bintray.com/')) {
                    project.logger.lifecycle "Repository ${repo.url} replaced by $ALIYUN_JCENTER_URL."
                    remove repo
                }
            }
        }
        maven {
            url ALIYUN_REPOSITORY_URL
            url ALIYUN_JCENTER_URL
        }
    }
}

测试代码

运行ProjectImportedOKTest单测，如果通过说明环境没有问题

我的运行结果如下：

> Configure project :
Repository https://jcenter.bintray.com/ replaced by http://maven.aliyun.com/nexus/content/repositories/jcenter.
> Task :compileJava
> Task :processResources NO-SOURCE
> Task :classes
> Task :compileTestJava
> Task :processTestResources NO-SOURCE
> Task :testClasses
> Task :test

代码开发

State开发

一个state需要实现ContractState，ContractState中有一个方法getParticipants()，返回的是List<AbstractParty>,表示在这个state发生了交易时需要通知谁，让谁知道。

package bootcamp;
import com.google.common.collect.ImmutableList;
import net.corda.core.contracts.ContractState;
import net.corda.core.identity.AbstractParty;
import net.corda.core.identity.Party;
import org.jetbrains.annotations.NotNull;
import java.util.List;
public class IouState implements ContractState {
    /**
     * 发行人
     */
    private Party issuer;
    /**
     * 拥有者
     */
    private Party owner;
    /**
     * 金额
     */
    private int amount;
    public IouState(Party issuer, Party owner, int amount) {
        this.issuer = issuer;
        this.owner = owner;
        this.amount = amount;
    }
    @NotNull
    @Override
    public List<AbstractParty> getParticipants() {
        return ImmutableList.of(issuer, owner);
    }
    public Party getIssuer() {
        return issuer;
    }
    public Party getOwner() {
        return owner;
    }
    public int getAmount() {
        return amount;
    }
}

Contract开发

一个contract简单的理解就是一些校验的规则，需要实现Contract类，Contract类如下，只有一个verify方法，验证LedgerTransaction是否正确，如果不正确就抛IllegalArgumentException异常。

interface Contract {
    /**
     * Takes an object that represents a state transition, and ensures the inputs/outputs/commands make sense.
     * Must throw an exception if there's a problem that should prevent state transition. Takes a single object
     * rather than an argument so that additional data can be added without breaking binary compatibility with
     * existing contract code.
     */
    @Throws(IllegalArgumentException::class)
    fun verify(tx: LedgerTransaction)
}

在开发一个contract时，Corda提议的三个验证的类型：

输入与输出个数的校验（Shape Constraint，No. input states, No. output states, command）
输入与输出的内容的校验（Context Constraint），业务校验
需要的签名的校验（Required Singer Constraint）

区块链实战-如何开发一个CorDapp - 图1

按照上图的规则IouContract的实现如下：

package bootcamp;
import net.corda.core.contracts.Command;
import net.corda.core.contracts.CommandData;
import net.corda.core.contracts.Contract;
import net.corda.core.contracts.ContractState;
import net.corda.core.transactions.LedgerTransaction;
import org.apache.commons.collections4.CollectionUtils;
public class IouContract implements Contract {
    public static String ID = "bootcamp.IouContract";
    @Override
    public void verify(LedgerTransaction tx) {
        // 1、Shape Constraint，No. input states, No. output states, command
        if (tx.getCommands().size() != 1) {
            throw new IllegalArgumentException("command size must be one");
        }
        Command<CommandData> command = tx.getCommand(0);
        if (!(command.getValue() instanceof Commands.Issue)) {
            throw new IllegalArgumentException("command must be Issue");
        }
        if (CollectionUtils.isNotEmpty(tx.getInputs())) {
            throw new IllegalArgumentException("Issue must be not inputs");
        }
        if (tx.getOutputs().size() != 1) {
            throw new IllegalArgumentException("Issue outputs must be one");
        }
        ContractState output = tx.getOutput(0);
        // 2、Context Constraint
        if (!(output instanceof IouState)) {
            throw new IllegalArgumentException("state must be IouState");
        }
        IouState iouState = (IouState) output;
        if (iouState.getAmount() <= 0) {
            throw new IllegalArgumentException("issue amount must big than zero");
        }
        // 3、Required Singer Constraint
        if (!command.getSigners().contains(iouState.getIssuer().getOwningKey())) {
            throw new IllegalArgumentException("issue business must be sing by issuer");
        }
    }
    public interface Commands extends CommandData {
        class Issue implements Commands {
        }
    }
}

Flow开发

flow有两种

可以在本地主动启动的flow
只能通过其他的flow启动的flow

发起一个交易的flow都是可以在本地主动启动的flow，有以下特点

需要添加注解@InitiatingFlow来表示他是一个可以初始化的flow
需要添加注@StartableByRPC或者@StartableByService来说明启动的方式
flow需要继承自FlowLogic，业务逻辑在call方法中实现
call方法需要添加@Suspendable注解
指定notary，校验是否双花
创建交易，交易中必须包含command，如果有output必须指定contract来进行验证；可以没有input
然后就是通用的流程，验证交易、收集签名、交易入库

package bootcamp;
import co.paralleluniverse.fibers.Suspendable;
import com.google.common.collect.ImmutableList;
import net.corda.core.contracts.StateAndRef;
import net.corda.core.flows.*;
import net.corda.core.identity.Party;
import net.corda.core.transactions.SignedTransaction;
import net.corda.core.transactions.TransactionBuilder;
import net.corda.core.utilities.ProgressTracker;
import static java.util.Collections.singletonList;
/**
 *
 * @author nicai
 */
@InitiatingFlow
@StartableByRPC
public class IouIssueFlowInitiator extends FlowLogic<SignedTransaction> {
    private final Party owner;
    private final int amount;
    public IouIssueFlowInitiator(Party owner, int amount) {
        this.owner = owner;
        this.amount = amount;
    }
    private final ProgressTracker progressTracker = new ProgressTracker();
    @Override
    public ProgressTracker getProgressTracker() {
        return progressTracker;
    }
    @Suspendable
    @Override
    public SignedTransaction call() throws FlowException {
        // We choose our transaction's notary (the notary prevents double-spends).
        Party notary = getServiceHub().getNetworkMapCache().getNotaryIdentities().get(0);
        // We get a reference to our own identity.
        Party issuer = getOurIdentity();
        // We create our new IouState.
        IouState iouState = new IouState(issuer, owner, amount);
        // We build our transaction.
        TransactionBuilder transactionBuilder = new TransactionBuilder(notary)
//                .addInputState()
                .addOutputState(iouState, IouContract.ID)
                .addCommand(new IouContract.Commands.Issue(), ImmutableList.of(issuer.getOwningKey(), owner.getOwningKey()));
        // We check our transaction is valid based on its contracts.
        transactionBuilder.verify(getServiceHub());
        FlowSession session = initiateFlow(owner);
        // We sign the transaction with our private key, making it immutable.
        SignedTransaction signedTransaction = getServiceHub().signInitialTransaction(transactionBuilder);
        // The counterparty signs the transaction
        SignedTransaction fullySignedTransaction = subFlow(new CollectSignaturesFlow(signedTransaction, singletonList(session)));
        // We get the transaction notarised and recorded automatically by the platform.
        return subFlow(new FinalityFlow(fullySignedTransaction, singletonList(session)));
    }
}

被动启动的flow有以下特点：

需要注解@InitiatedBy(IouIssueFlowInitiator.class)指定谁能启动这个flow
flow需要继承自FlowLogic，业务逻辑在call方法中实现
call方法需要添加@Suspendable注解
需要有实例变量FlowSession，保存调用者的FlowSession
call方法需要验证交易，然后执行接收交易的标准流程ReceiveFinalityFlow

package bootcamp;
import co.paralleluniverse.fibers.Suspendable;
import net.corda.core.flows.*;
import net.corda.core.transactions.SignedTransaction;
@InitiatedBy(IouIssueFlowInitiator.class)
public class IouIssueFlowResponder extends FlowLogic<Void> {
    private final FlowSession otherSide;
    public IouIssueFlowResponder(FlowSession otherSide) {
        this.otherSide = otherSide;
    }
    @Override
    @Suspendable
    public Void call() throws FlowException {
        SignedTransaction signedTransaction = subFlow(new SignTransactionFlow(otherSide) {
            @Suspendable
            @Override
            protected void checkTransaction(SignedTransaction stx) throws FlowException {
                // Implement responder flow transaction checks here
            }
        });
        subFlow(new ReceiveFinalityFlow(otherSide, signedTransaction.getId()));
        return null;
    }
}

运行

打包

./gradlew deployNodes

运行所有的节点

sudo ./build/nodes/runnodes

启动一个流程

flow start IouIssueFlow owner: PartyB, amount: 99

我本地日志如下：

 ✅   Starting
          Requesting signature by notary service
              Requesting signature by Notary service
              Validating response from Notary service
     ✅   Broadcasting transaction to participants
➡️   Done
Flow completed with result: SignedTransaction(id=14D268667D208D26BF92ADC1F58003DFC9EAF7E036ACB2C2CABC153E627500C0)

查询生成的数据

 run vaultQuery contractStateType: bootcamp.IouState

我本地的结果如下

states:
- state:
    data: !<bootcamp.IouState>
      issuer: "O=PartyA, L=London, C=GB"
      owner: "O=PartyB, L=New York, C=US"
      amount: 99
    contract: "bootcamp.IouContract"
    notary: "O=Notary, L=London, C=GB"
    encumbrance: null
    constraint: !<net.corda.core.contracts.SignatureAttachmentConstraint>
      key: "aSq9DsNNvGhYxYyqA9wd2eduEAZ5AXWgJTbTEw3G5d2maAq8vtLE4kZHgCs5jcB1N31cx1hpsLeqG2ngSysVHqcXhbNts6SkRWDaV7xNcr6MtcbufGUchxredBb6"
  ref:
    txhash: "14D268667D208D26BF92ADC1F58003DFC9EAF7E036ACB2C2CABC153E627500C0"
    index: 0
statesMetadata:
- ref:
    txhash: "14D268667D208D26BF92ADC1F58003DFC9EAF7E036ACB2C2CABC153E627500C0"
    index: 0
  contractStateClassName: "bootcamp.IouState"
  recordedTime: "2020-12-03T09:49:48.373Z"
  consumedTime: null
  status: "UNCONSUMED"
  notary: "O=Notary, L=London, C=GB"
  lockId: null
  lockUpdateTime: null
  relevancyStatus: "RELEVANT"
  constraintInfo:
    constraint:
      key: "aSq9DsNNvGhYxYyqA9wd2eduEAZ5AXWgJTbTEw3G5d2maAq8vtLE4kZHgCs5jcB1N31cx1hpsLeqG2ngSysVHqcXhbNts6SkRWDaV7xNcr6MtcbufGUchxredBb6"
totalStatesAvailable: -1
stateTypes: "UNCONSUMED"
otherResults: []

节点可视化工具

参考网站：https://docs.corda.net/docs/corda-os/4.6/node-explorer.html

可以下载node-explorer来查看节点信息。

第一次打开界面

区块链实战-如何开发一个CorDapp - 图2

Node Hostname：localhost
Node Port：RPC connection address可以在启动的窗口查看，或者配置文件查看
RPC Username：在配置文件
RPC Password:在配置文件查看

区块链实战-如何开发一个CorDapp - 图3

区块链实战-如何开发一个CorDapp - 图4

使用spring开发corda：

https://manosbatsis.github.io/corbeans/