【web3j】java通过web3j监听并解析合约中的事件(event/emit)

① 查询链上数据用的rpc（本示例是binance的，测试网可以使用：https://data-seed-prebsc-2-s2.binance.org:8545）

② 自己还要有一个测试链上部署好的合约，合约中要有一个方法emit了事件。

③ java依赖

<dependency><groupId>org.web3j</groupId><artifactId>core</artifactId><version>4.9.7</version>
</dependency>
<dependency><groupId>org.web3j</groupId><artifactId>codegen</artifactId><version>4.9.7</version>
</dependency>

一、通过自己合约的abi和bin生成一个java文件，abi和bin可以在remix的compiler模块中获取，代码如下（这一步懒得做的可以跳过，在第二步传合约地址的时候，直接传一个字符串也行。这里就是顺手存一下这个方法，其实实际使用也是直接传的字符串，具体可以看页面最下方的”三、“）

    /* 通过合约abi和bin获得java文件*/public void getJavaFileBySolidity(){// 生成的java类名，同ABI文件同名，自动首字母大写String packageName = "";String outDirPath = "/Users/maomo/Desktop/";String binDirPath = "/Users/maomo/Desktop/xxxbin.txt";String abiDirPath = "/Users/maomo/Desktop/xxxabi.txt";String[] arr = Arrays.asList("-b", binDirPath,"-a", abiDirPath,"-p", packageName,"-o", outDirPath).toArray(new String[0]);SolidityFunctionWrapperGenerator.main(arr);}

二、通过web3j查询事件，通过event和ethFilter增加过滤条件

    public void testSub() {Web3j web3j = Web3j.build(new HttpService("https://data-seed-prebsc-2-s2.binance.org:8545"));//第一步生成的合约实体Contract contract;Disposable subscribe = null;try {Web3ClientVersion web3ClientVersion = web3j.web3ClientVersion().send();String clientVersion = web3ClientVersion.getWeb3ClientVersion();log.info("wen3j subscribe --clientVersion-- :{} ", clientVersion);//设置谁调用合约TransactionManager transactionManager = new ClientTransactionManager(web3j, "这里可以输入自己的钱包地址");//加载智能合约（此处可以跳过，下面穿合约地址的地方 直接传字符串）contract = Contract.load("你要监听的合约地址", web3j, transactionManager, ManagedTransaction.GAS_PRICE, org.web3j.tx.Contract.GAS_LIMIT);//设置过滤条件 这个示例是监听最新的1000个块BigInteger blockNumber = web3j.ethBlockNumber().send().getBlockNumber().subtract(new BigInteger("1000"));EthFilter ethFilter = new EthFilter(DefaultBlockParameter.valueOf(blockNumber),DefaultBlockParameterName.LATEST, contract.getContractAddress());//监听哪个事件，合约中的event写了几个参数，这里就写几个，类型对应好Event event = new Event("startEvent",Arrays.<TypeReference<?>>asList(new TypeReference<Address>(true) {},new TypeReference<Address>(true) {},new TypeReference<Uint256>(true) {},new TypeReference<Uint256>(false) {},new TypeReference<Uint256>(false) {},new TypeReference<Uint256>(false) {}));ethFilter.addSingleTopic(EventEncoder.encode(event));subscribe = web3j.ethLogFlowable(ethFilter).subscribe(tx -> {int newBlock = tx.getBlockNumber().intValue();log.info("wen3j subscribe --newBlock-- :{} ", newBlock);log.info("wen3j subscribe --tx-- :{} ", tx);EventValues eventValues = staticExtractEventParameters(event, tx);//定义接收参数(本示例使用的事件返回了6个，具体按自己合约来)String address1 = "";String address2 = "";int uint1 = 0;int uint2 = 0;int uint3 = 0;int uint4 = 0;List<Type> indexedValues = eventValues.getIndexedValues();if (ObjectUtils.isNotEmpty(indexedValues) && indexedValues.size() == 3) {Type type1 = indexedValues.get(0);address1 = type1.getValue().toString();Type type2 = indexedValues.get(1);address2 = type2.getValue().toString();Type type3 = indexedValues.get(2);uint1 = Integer.parseInt(type3.getValue().toString());}List<Type> nonIndexedValues = eventValues.getNonIndexedValues();if (ObjectUtils.isNotEmpty(nonIndexedValues) && nonIndexedValues.size() == 3) {Type type1 = nonIndexedValues.get(0);uint2 = Integer.parseInt(type1.getValue().toString());Type type2 = nonIndexedValues.get(1);uint3 = Integer.parseInt(type2.getValue().toString());Type type3 = nonIndexedValues.get(2);uint4 = Integer.parseInt(type3.getValue().toString());}log.info("address1:{};address2:{};uint1:{};uint2:{};uint3:{};uint4:{}",address1, address2, uint1, uint2, uint3, uint4);});}catch (Exception e) {e.printStackTrace();}finally {//关闭监听if(ObjectUtils.isNotEmpty(subscribe) && !subscribe.isDisposed()){subscribe.dispose();}}}

    /* 解析log返回的data* @param event 合约中定义的事件* @param log 监听到的log* @return 解析后的数据*/public EventValues staticExtractEventParameters(Event event, Log log) {final List<String> topics = log.getTopics();String encodedEventSignature = EventEncoder.encode(event);if (topics == null || topics.size() == 0 || !topics.get(0).equals(encodedEventSignature)) {return null;}List<Type> indexedValues = new ArrayList<>();List<Type> nonIndexedValues = FunctionReturnDecoder.decode(log.getData(), event.getNonIndexedParameters());List<TypeReference<Type>> indexedParameters = event.getIndexedParameters();for (int i = 0; i < indexedParameters.size(); i++) {Type value = FunctionReturnDecoder.decodeIndexedValue(topics.get(i + 1), indexedParameters.get(i));indexedValues.add(value);}return new EventValues(indexedValues, nonIndexedValues);}

三、为了方便以后复制粘贴(不是)，最下面再传一个不生成合约的版本

    public void testSub() {Web3j web3j = Web3j.build(new HttpService("https://data-seed-prebsc-2-s2.binance.org:8545"));//第一步生成的合约实体Contract contract;Disposable subscribe = null;try {Web3ClientVersion web3ClientVersion = web3j.web3ClientVersion().send();String clientVersion = web3ClientVersion.getWeb3ClientVersion();log.info("wen3j subscribe --clientVersion-- :{} ", clientVersion);//设置过滤条件 这个示例是监听最新的1000个块BigInteger blockNumber = web3j.ethBlockNumber().send().getBlockNumber().subtract(new BigInteger("1000"));EthFilter ethFilter = new EthFilter(DefaultBlockParameter.valueOf(blockNumber),DefaultBlockParameterName.LATEST, "输入合约地址");//监听哪个事件，合约中的event写了几个参数，这里就写几个，类型对应好Event event = new Event("startEvent",Arrays.<TypeReference<?>>asList(new TypeReference<Address>(true) {},new TypeReference<Address>(true) {},new TypeReference<Uint256>(true) {},new TypeReference<Uint256>(false) {},new TypeReference<Uint256>(false) {},new TypeReference<Uint256>(false) {}));ethFilter.addSingleTopic(EventEncoder.encode(event));subscribe = web3j.ethLogFlowable(ethFilter).subscribe(tx -> {int newBlock = tx.getBlockNumber().intValue();log.info("wen3j subscribe --newBlock-- :{} ", newBlock);log.info("wen3j subscribe --tx-- :{} ", tx);EventValues eventValues = staticExtractEventParameters(event, tx);//定义接收参数(本示例使用的事件返回了6个，具体按自己合约来)String address1 = "";String address2 = "";int uint1 = 0;int uint2 = 0;int uint3 = 0;int uint4 = 0;List<Type> indexedValues = eventValues.getIndexedValues();if (ObjectUtils.isNotEmpty(indexedValues) && indexedValues.size() == 3) {Type type1 = indexedValues.get(0);address1 = type1.getValue().toString();Type type2 = indexedValues.get(1);address2 = type2.getValue().toString();Type type3 = indexedValues.get(2);uint1 = Integer.parseInt(type3.getValue().toString());}List<Type> nonIndexedValues = eventValues.getNonIndexedValues();if (ObjectUtils.isNotEmpty(nonIndexedValues) && nonIndexedValues.size() == 3) {Type type1 = nonIndexedValues.get(0);uint2 = Integer.parseInt(type1.getValue().toString());Type type2 = nonIndexedValues.get(1);uint3 = Integer.parseInt(type2.getValue().toString());Type type3 = nonIndexedValues.get(2);uint4 = Integer.parseInt(type3.getValue().toString());}log.info("address1:{};address2:{};uint1:{};uint2:{};uint3:{};uint4:{}",address1, address2, uint1, uint2, uint3, uint4);});}catch (Exception e) {e.printStackTrace();}finally {//关闭监听if(ObjectUtils.isNotEmpty(subscribe) && !subscribe.isDisposed()){subscribe.dispose();}}}

=========================分割线=========================

还有一种把web3j.ethLogFlowable(ethFilter).subscribe换成查询的方法，做个记录

把这段代码

subscribe = web3j.ethLogFlowable(ethFilter).subscribe(tx -> {//逻辑...
}

换成

List<EthLog.LogResult> resp = web3j.ethGetLogs(ethFilter).send().getLogs();for (EthLog.LogResult logItem : resp) {EthLog.LogObject tx = ObjectUtils.isNotEmpty(logItem.get()) ? (EthLog.LogObject) logItem.get() : null;if(ObjectUtils.isEmpty(tx)){return false;}//逻辑...}