BitCoinJ之Hello World示例程序

簡介

比特幣(BitCoin)是一種基於區塊鏈(BlockChain)技術的數字化貨幣. 本文介紹了使用基於Java語言的BitCoinJ API實現一個簡單的收取和支付比特幣的示例程序.

開發環境

本示例使用BitCoinJ(https://bitcoinj.github.io/) API, 目前的發布版本是0.14.3, 其JAR包可以從官網下載, 也可以通過如下的Maven定義在項目POM中引用.

<dependencies>
   <dependency>
     <groupId>org.bitcoinj</groupId>
     <artifactId>bitcoinj-core</artifactId>
     <version>0.14.3</version>
     <scope>compile</scope>
   </dependency>
 </dependencies>

收取比特幣

收取比特幣的示例代碼如下

public class BitCoinHelloWorld implements WalletCoinsReceivedEventListener {

    publicstaticvoidmain(String[] args) {
        BitCoinHelloWorld demo = new BitCoinHelloWorld();

        demo.run();
    }

    publicvoidrun() {
        try {
            init();

            System.out.println("Waiting for coins...");

            while (true) {
                Thread.sleep(20);
            }
        } catch (BlockStoreException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    privatevoidinit() throws BlockStoreException {
        NetworkParameters params  = TestNet3Params.get();

        ECKey key = new ECKey();
        System.out.println("We created a new key:\n" + key);

        Address addressFromKey = key.toAddress(params);
        System.out.println("Public Address generated: " + addressFromKey);

        System.out.println("Private key is: " + key.getPrivateKeyEncoded(params).toString());

        Wallet wallet = new Wallet(params);
        wallet.importKey(key);

        File blockFile = new File("/tmp/bitcoin-blocks");
        SPVBlockStore blockStore = new SPVBlockStore(params, blockFile);

        BlockChain blockChain = new BlockChain(params, wallet, blockStore);
        PeerGroup peerGroup = new PeerGroup(params, blockChain);
        peerGroup.addPeerDiscovery(new DnsDiscovery(params));
        peerGroup.addWallet(wallet);

        System.out.println("Start peer group");
        peerGroup.start();

        System.out.println("Downloading block chain");
        peerGroup.downloadBlockChain();
        System.out.println("Block chain downloaded");

        wallet.addCoinsReceivedEventListener(this);
    }


    @Override
    publicvoidonCoinsReceived(final Wallet wallet, final Transaction transaction, Coin prevBalance, Coin newBalance) {
        final Coin value = transaction.getValueSentToMe(wallet);

        System.out.println("Received tx for " + value.toFriendlyString() + ": " + transaction);

        System.out.println("Previous balance is " + prevBalance.toFriendlyString());

        System.out.println("New estimated balance is " + newBalance.toFriendlyString());

        System.out.println("Coin received, wallet balance is :" + wallet.getBalance());

        Futures.addCallback(transaction.getConfidence().getDepthFuture(1), new FutureCallback<TransactionConfidence>() {
            publicvoidonSuccess(TransactionConfidence result) {
                System.out.println("Transaction confirmed, wallet balance is :" + wallet.getBalance());
            }

            publicvoidonFailure(Throwable t) {
                t.printStackTrace();
            }
        });
    }
}

該示例程序首先調用init方法進行初始化, 然後進入一個等待循環, 當有比特幣到來時, onCoinsReceived方法就被觸發.

各個步驟的具體分析如下

選擇運行環境

比特幣應用可以在三種不同的環境中運行: 正式流通網絡, 測試流通網絡以及本地開發環境. 初始化的第一步是通過設置一個NetworkParameters變量來選擇運行環境, 以下代碼使用測試流通網絡

NetworkParameters params  = TestNet3Params.get();

獲取地址和設置錢包對象

以下代碼首先創建一個可用於接受比特幣的地址, 並將其導入相應的錢包對象中.

ECKey key = new ECKey();
System.out.println("We created a new key:\n" + key);

Address addressFromKey = key.toAddress(params);
System.out.println("Public Address generated: " + addressFromKey);

System.out.println("Private key is: " + key.getPrivateKeyEncoded(params).toString());

Wallet wallet = new Wallet(params);
wallet.importKey(key);

接入流通網絡並下載比特幣區塊

以下代碼接入流通網絡並下載比特幣區塊

File blockFile = new File("/tmp/bitcoin-blocks");
SPVBlockStore blockStore = new SPVBlockStore(params, blockFile);

BlockChain blockChain = new BlockChain(params, wallet, blockStore);
PeerGroup peerGroup = new PeerGroup(params, blockChain);
peerGroup.addPeerDiscovery(new DnsDiscovery(params));
peerGroup.addWallet(wallet);

System.out.println("Start peer group");
peerGroup.start();

System.out.println("Downloading block chain");
peerGroup.downloadBlockChain();
System.out.println("Block chain downloaded");

需要注意的是peerGroup.downloadBlockChain();這一步可能會運行很長時間.

設置事件響應

以下代碼設置當比特幣到來時的事件響應

wallet.addCoinsReceivedEventListener(this);

比特幣到來事件響應

當比特幣到來時onCoinsReceived方法就會觸發, 注意該方法的newBalance參數提供的是錢包中金額的估計值,其實際金額要等到交易被網絡確認後才會提現在wallet.getBalance()的返回值中, 如以下代碼所示

Futures.addCallback(transaction.getConfidence().getDepthFuture(1), new FutureCallback<TransactionConfidence>() {
    publicvoidonSuccess(TransactionConfidence result) {
        System.out.println("Transaction confirmed, wallet balance is :" + wallet.getBalance());
    }

    publicvoidonFailure(Throwable t) {
        t.printStackTrace();
    }
});

支付比特幣

支付比特幣的過程相對簡單, 首選設置要支付的金額.

final Coin amountToSend = Coin.valueOf(10, 0);

其次設置接收方的地址

Address toAddress = Address.fromBase58(params, "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi");

然後發送該支付交易

final Wallet.SendResult sendResult = wallet.sendCoins(peerGroup, toAddress, amountToSend);

並設置交易完成後的事件響應

sendResult.broadcastComplete.addListener(new Runnable() {
  @Override
  publicvoidrun() {
      System.out.println("Coins Sent! Transaction hash is " + sendResult.tx.getHashAsString());
  }
}, MoreExecutors.sameThreadExecutor());

總結

本文給出了一個基於BitCoinJ的比特幣收發示例程序, 並對BitCoinJ的編程模式以及其事件響應機制做了初步介紹。