web3j學習(1)

本文源代碼見 https://github.com/pigeon2049/planet-universal

作為一個寫 java 的全棧開發，sodility 語言似乎讓人很難下手，所以先從熟悉的領域入手

web3j

起手一個傳統 springboot maven 項目，引用 web3j 依賴

<dependency>
    <groupId>org.web3j</groupId>
    <artifactId>core</artifactId>
    <version>${web3j.version}</version>
</dependency>
<dependency>
    <groupId>org.web3j</groupId>
    <artifactId>contracts</artifactId>
    <version>${web3j.version}</version>
</dependency>

為了快速開發學習，本機需要安裝 docker

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-docker-compose</artifactId>
  <scope>runtime</scope>
  <optional>true</optional>
</dependency>

新版本 springboot 支持集成 docker, 所以沒有安裝環境的過程，直接啟，會得到一個 ipfs kubo 客戶端以及 influxdb 時序數據庫

開始學習:
web3j 需要一個以太坊客戶端節點，可以自己用 geth 搭一個，也可以偷懶使用 cloudflare 提供的公共端口，使用公共端口注意儘量不要使用自己的地址和密鑰與合約交互，容易產生安全問題

application.properties 添加 cloudflare eth gateway

web3j.node.address=https://cloudflare-eth.com/

定義一個配置文件，生成 web3j 的 bean


@Configuration
public class Web3jConfig {

    @Value("${web3j.node.address}")
    private String ethNode;

    @Bean
    public Web3j web3j() throws ExecutionException, InterruptedException {
        Web3j build = Web3j.build(new HttpService(ethNode));
        Web3ClientVersion web3ClientVersion = build.web3ClientVersion().sendAsync().get();
        System.out.println(web3ClientVersion.getWeb3ClientVersion());
        return build;
    }
}

這樣我們就得到了一个可用的 web3j client

接下來簡單寫個獲取以太坊鏈上實時 Gas 費的方法

@Service
public class GasPrice {

    private final Web3j web3j;


    public GasPrice(Web3j web3j) {
        this.web3j = web3j;
    }


    public BigInteger gasGasPrice() throws IOException {

        return web3j.ethGasPrice().send().getGasPrice();
    }



}

是不是很簡單？

但是你就會發現這個單位好像不對，平時看到的是 Gwei
, 換算一下

BigInteger gas = gasPrice.gasGasPrice();
BigDecimal value= BigDecimal.valueOf(gas .longValue() * 0.000000001).setScale(2, RoundingMode.HALF_UP);

保留兩位小數，得到的就是 Gwei 了

簡單寫個定時，每秒獲取一次 Gas 數據存數據庫

@Service
public class UpdateGasPrice implements CommandLineRunner {

    @Value("${influx.url}")
    String url;

    @Value("${influx.token}")
    String token;

    @Value("${influx.org}")
    String org ;

    @Value("${influx.bucket}")
    String bucket ;

    private final GasPrice gasPrice;

    public UpdateGasPrice(GasPrice gasPrice) {
        this.gasPrice = gasPrice;
    }

    @Override
    public void run(String... args) throws Exception {
        InfluxDBClient client = InfluxDBClientFactory.create(url, token.toCharArray(), org, bucket)
                .setLogLevel(LogLevel.BASIC);
        WriteApi writeApi = client.makeWriteApi(WriteOptions.builder().flushInterval(2_000).build());

        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {

                try {
                    BigInteger gas = gasPrice.gasGasPrice();
                    if (gas!=null){
                        BigDecimal value= BigDecimal.valueOf(gas.longValue() * 0.000000001).setScale(2, RoundingMode.HALF_UP);
                        Point point = Point
                                .measurement("eth")
                                .addField("gas", gas.longValue())
                                .addField("gasGwei", value)
                                .time(Instant.now(), WritePrecision.S);

                        System.out.println("Produced DataPoint: " + point.toLineProtocol());

                        writeApi.writePoint(point);
                    }


                } catch (IOException ignored) {}

            }
        }, 0, 1000);

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            System.out.println("Close Client and Producer");
            timer.cancel();
            client.close();
        }));
    }
}

運行代碼

打開http://localhost:8086
進入 influxdb 的管理網頁，密碼寫在 env 裡

可以看到已經開始寫入 gas 數據了

獲取地址以太坊餘額

以太坊鏈上就很簡單


  public BigDecimal getBalance(String address) throws IOException {
      BigInteger balance = web3j.ethGetBalance(address, DefaultBlockParameterName.LATEST).send().getBalance();
      BigDecimal ether = Convert.fromWei(String.valueOf(balance), Convert.Unit.ETHER);
      System.out.println(address+" balance:"+ether.toString());
      return  ether;
  }

獲取 Erc20 代幣餘額


public BigDecimal getErc20Balance(String address,String tokenContractAddress) throws Exception {

        // Use ReadOnlyTransactionManager for read-only operations
        ReadonlyTransactionManager txManager = new ReadonlyTransactionManager(web3j, null);
        DefaultGasProvider gasPriceProvider = new DefaultGasProvider();
        // ERC20 is your generated ERC20 contract wrapper class
        ERC20 contract = ERC20.load(tokenContractAddress, web3j, txManager, gasPriceProvider);

        // Call the balanceOf function on the ERC-20 contract
        BigInteger balance = contract.balanceOf(address).send();
        BigDecimal ether = Convert.fromWei(String.valueOf(balance), Convert.Unit.ETHER);
        System.out.println("Balance of " + address + ": " + ether);

        return ether;
    }

本次學習了簡易的鏈上操作，只是簡易讀取
後續加深學習合約交互