Web3j通過合約地址監聽transfer事件獲取以太坊交易數據

web3j是一個輕量級的Java庫，用於在Ethereum網絡上集成客戶端（節點）。

核心特性

• 通過Java類型的JSON-RPC與Ethereum客戶端進行交互
• 支持所有的JSON-RPC方法類型
• 支持所有Geth和Parity方法，用於管理賬戶和簽署交易
• 同步或異步的發送客戶端請求
• 可從Solidity ABI文件自動生成Java只能合約功能包

業務需求: 分析區塊鏈轉賬記錄，獲取交易信息進一步分析。

原創代碼，用web3j接入以太坊全節點，通過合約地址監聽transfer事件，獲取交易記錄。

注意：注意版本問題。不同版本event的構造參數列表是不一樣的。

	<dependency>
		<groupId>org.web3j</groupId>
		<artifactId>core</artifactId>
		<version>3.4.0</version>
  	</dependency>

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@Service
public class MonitorTransferService {

    private static final Logger LOG = LoggerFactory.getLogger(MonitorTransferService.class);
    private Web3j web3j;
    private ThreadLocal<Set<BigInteger>> blockNumberSet = ThreadLocal.withInitial(HashSet::new);

    @Value("${ipcSocketPath}")
    private String ipcSocketPath;

    @PostConstruct
    public void init() {
//        web3j = Web3j.build(new HttpService()); //RPC方式
        web3j = Web3j.build(new UnixIpcService(ipcSocketPath)); //IPC方式
    }

    /**
     * 監聽合約(分步)
     */
    public void contractFilterOfStep(MonitorTransferRequest monitorTransferRequest) {
        new Thread(() -> {
            try {
                BigInteger blockNumber = getBlockNumber();
                LOG.info("BlockChainNumber={}", blockNumber);
                BigInteger startBlock = new BigInteger(monitorTransferRequest.getFirstBlock());
                BigInteger step = new BigInteger("100");
                assert blockNumber != null;
                int num = Integer.parseInt(String.valueOf(blockNumber.subtract(startBlock).divide(step)));
                for (int i = 0; i < num; i++) {
                    // 監聽合約(分步)
                    contractFilterStep(monitorTransferRequest, startBlock, startBlock.add(step));
                    startBlock = startBlock.add(step);
                }
                // 監聽合約
                contractFilter(monitorTransferRequest, startBlock);
            } catch (NumberFormatException e) {
                LOG.error("監控合約異常終止,e={}", e.getMessage());
            }
        }).start();
    }

    /**
     * 監聽合約
     */
    private void contractFilter(MonitorTransferRequest monitorTransferRequest, BigInteger startBlock) {
        Event event = new Event("Transfer",
                Arrays.asList(
                        new TypeReference<Address>() {
                        },
                        new TypeReference<Address>() {
                        }),
                Collections.singletonList(new TypeReference<Uint256>() {
                }));
        EthFilter filter = new EthFilter(
                DefaultBlockParameter.valueOf(startBlock),
                DefaultBlockParameterName.LATEST,
                monitorTransferRequest.getContractAddress());
        filter.addSingleTopic(EventEncoder.encode(event));
        // 監聽並處理
        contractExtract(filter);
    }

    /**
     * 監聽並處理
     */
    private void contractExtract(EthFilter filter) {
        Subscription subscription = web3j.ethLogObservable(filter).subscribe(log -> {
            BigInteger blockNumber = log.getBlockNumber();
            // 提取轉賬記錄
            LOG.info("BlockNumber=", blockNumber);
            blockNumberSet.get().add(blockNumber);
            List<String> topics = log.getTopics();
            String fromAddress = topics.get(1);
            String toAddress = topics.get(2);
            String value = log.getData();
            String timestamp = "";

            try {
                EthBlock ethBlock = web3j.ethGetBlockByNumber(DefaultBlockParameter.valueOf(log.getBlockNumber()), false).send();
                timestamp = String.valueOf(ethBlock.getBlock().getTimestamp());
            } catch (IOException e) {
                LOG.warn("Block timestamp get failure,block number is {}", log.getBlockNumber());
                LOG.error("Block timestamp get failure,{}", e);
            }

            TransferRecord transferRecord = new TransferRecord();
            transferRecord.setFromAddress("0x" + fromAddress.substring(26));
            transferRecord.setToAddress("0x" + toAddress.substring(26));
            transferRecord.setValue(new BigDecimal(new BigInteger(value.substring(2), 16)).divide(BigDecimal.valueOf(1000000000000000000.0), 18, BigDecimal.ROUND_HALF_EVEN));
            transferRecord.setTimeStamp(timestamp);
        });
//        subscription.unsubscribe();
    }

    /**
     * 監聽合約(分步)
     */
    private void contractFilterStep(MonitorTransferRequest monitorTransferRequest, BigInteger startBlock, BigInteger endBlock) {
        Event event = new Event("Transfer",
                Arrays.asList(
                        new TypeReference<Address>() {
                        },
                        new TypeReference<Address>() {
                        }),
                Collections.singletonList(new TypeReference<Uint256>() {
                }));
        EthFilter filter = new EthFilter(
                DefaultBlockParameter.valueOf(startBlock),
                DefaultBlockParameter.valueOf(endBlock),
                monitorTransferRequest.getContractAddress());
        filter.addSingleTopic(EventEncoder.encode(event));
        // 監聽並處理
        contractExtract(filter);
    }

    /**
     * 區塊數量
     */
    private BigInteger getBlockNumber() {
        EthBlockNumber send;
        try {
            send = web3j.ethBlockNumber().send();
            return send.getBlockNumber();
        } catch (IOException e) {
            LOG.warn("請求區塊鏈信息異常 >> 區塊數量,{}", e);
        }
        return null;
    }

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