web3j学习(1)

本文源代码见 https://github.com/pigeon2049/planet-universal

作为一个写 java 的全栈开发，sodility 语言似乎让人很难下手，所以先从熟悉的领域入手

web3j

起手一个传统 springboot maven 项目，引用 web3j 依赖

<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>

为了快速开发学习，本机需要安装 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, 所以没有安装环境的过程，直接启，会得到一个 ipfs kubo 客户端以及 influxdb 时序数据库

开始学习:
web3j 需要一个以太坊客户端节点，可以自己用 geth 搭一个，也可以偷懒使用 cloudflare 提供的公共端口，使用公共端口注意尽量不要使用自己的地址和密钥与合约交互，容易产生安全问题

application.properties 添加 cloudflare eth gateway

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

定义一个配置文件，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;
    }
}

这样我们就得到了一个可用的 web3j client

接下来简单写个获取以太坊链上实时 Gas 费的方法

@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();
    }



}

是不是很简单？

但是你就会发现这个单位好像不对，平时看到的是 Gwei
, 换算一下

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

保留两位小数，得到的就是 Gwei 了

简单写个定时，每秒获取一次 Gas 数据存数据库

@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();
        }));
    }
}

运行代码

打开http://localhost:8086
进入 influxdb 的管理网页，密码写在 env 里

可以看到已经开始写入 gas 数据了

获取地址以太坊余额

以太坊链上就很简单


  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;
  }

获取 Erc20 代币余额


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;
    }

本次学习了简易的链上操作，只是简易读取
后续加深学习合约交互