扫块监听逻辑

跑定时任务，每隔固定时间执行一次轮询，这里我采用的间隔时间是距上一次执行完后45秒；
定时任务：从上一次轮询的最后区块开始扫描，获取每个区块中所有交易，进行对应查询数据库操作和判断操作，执行完后记录轮询到的区块高度，方便下一次查询；

相关依赖

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>4.0.3</version>
</dependency>

• 以下是使用spring管理的定时任务方法案例：

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.DefaultBlockParameter;
import org.web3j.protocol.core.methods.response.EthBlock;
import org.web3j.protocol.http.HttpService;

import java.io.IOException;
import java.math.BigInteger;

@Component
public class TransactionWatcherExample {

    private Web3j web3j = Web3j.build(new HttpService("http://localhost:8545"));

    //上次轮询到的块高度
    private BigInteger lastBlockNumber;

    /**
     * 扫块监听eth交易，每45秒一次轮询
     * @throws IOException
     */
    @Scheduled(fixedDelay = 45 * 1000)
    public void watchEthTransaction() throws IOException {

        //获取当前块高度
        BigInteger currentBlockNumber = web3j.ethBlockNumber().send().getBlockNumber();

        //运行初始化
        if (lastBlockNumber == null || currentBlockNumber.subtract(lastBlockNumber).compareTo(BigInteger.valueOf(100)) > 0) {
            lastBlockNumber = BigInteger.valueOf(currentBlockNumber.longValue());
            return;
        }

        long futureBlockNum = currentBlockNumber.intValue() + 1;

        //遍历区块
        for (int i = lastBlockNumber.intValue(); i < futureBlockNum; i++) {

            //获取block
            EthBlock.Block block = web3j.ethGetBlockByNumber(DefaultBlockParameter.valueOf(BigInteger.valueOf(i)), true).send().getBlock();

            if (block == null) {
                continue;
            }

            // 遍历block中的交易
            for (EthBlock.TransactionResult tx : block.getTransactions()) {
                if (tx instanceof EthBlock.TransactionObject) {

                    //transaction: 块中的单笔交易
                    EthBlock.TransactionObject transaction = (EthBlock.TransactionObject) tx;


                    // todo 交易判断和处理逻辑


                }
            }
        }

        lastBlockNumber = BigInteger.valueOf(futureBlockNum);

    }

}