导语
接上篇文章 《使用hardhat部署solidity智能合约到测试网》
部署完合约之后，那么如何区块链进行交互呢？这节的主要内容就是使用web3.js和web3j来与区块链以及链上的合约进行交互。其中web3.js是属于javascript的版本的，
web3j是java版本的。
合约交互的类型
以太坊可以看做一个公共数据库，这个数据库提供了读、写功能，但是不能删除。
发起交易其实就是将交易写库，写库不能白写，其他节点帮你记录了数据，你要支付一些费用给帮你记录的节点，这个费用就是我们经常看到的gas。因此以太坊上所有对链上的数据进行更改的操作都是需要花费gas的，而读取是免费的。
我们可以简单将与合约交易的类型分成一下三种：
1. 只读调用 2. 支付gas的调用 3. 支付gas和value的调用
1，2两种我们上面也都谈到了，那么第三种是什么呢。第三种情况就是调用合约时将的ETH转到合约中，这个value就是这个转账的数值，合约是可以接受ETH的。
如果想要合约接收ETH需要，调用的方法加上payable关键字声明，除此之外合约还要有声明一个 receive()方法，表明此合约可以接收ETH.
在solidity 0.6.10中是receive，不同的版本方法的声明可能会有差异。
receive() payable external {}
言归正传，下面就开始进入正题
使用web3.js与合约交互
在项目中引入web3.js
npm install web3
项目骨架
var Web3 = require('web3');var web3 = new Web3("https://rinkeby.infura.io/v3/7d00bf84530c4264969a4f0f231de8b6");var privateKey = "私钥";var contractAbi = [{"inputs":[],"name":"getBalance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getName","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"payETH","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"string","name":"_name","type":"string"}],"name":"setName","outputs":[],"stateMutability":"nonpayable","type":"function"},{"stateMutability":"payable","type":"receive"}];var contractAddress = "0xb19c13d0A37cDDE5c1F969a0d9BD6a50B3A11B4E"var hello = new web3.eth.Contract(contractAbi, contractAddress);main().then(() => process.exit(0)).catch(error => {console.error(error);process.exit(1);});async function main(){await getName();}async function getName(){var name = await hello.methods.getName().call();console.log(name);}
只读调用
async function getName(){var name = await hello.methods.getName().call();console.log(name);}async function getBalance(){var balance = await hello.methods.getBalance().call();console.log("balance = "+balance);}
支付gas的调用
async function setName(){var name = "Jack";var functionEncode = await hello.methods.setName(name).encodeABI();var sign = await web3.eth.accounts.signTransaction({gas: 300000,to: contractAddress,data: functionEncode,}, privateKey);var result = await web3.eth.sendSignedTransaction(sign.rawTransaction);console.log("setName txHash = "+result.transactionHash);}
支付gas和value的调用
async function reviceETH(){var ethValue = 100;var functionEncode = await hello.methods.reviceETH().encodeABI();var sign = await web3.eth.accounts.signTransaction({gas: 300000, to: contractAddress,data: functionEncode,value: ethValue}, privateKey);var result = await web3.eth.sendSignedTransaction(sign.rawTransaction);console.log("reviceETH resultTxHash = "+result.transactionHash);}
执行结果
使用web3j与合约交互
这里使用的是maven项目，第一步要引入web3j的包
引入pom
<dependency><groupId>org.web3j</groupId><artifactId>core</artifactId><version>3.4.0</version></dependency>
代码
Java 版本的直接上代码，也就是上述三种方式的调用
import org.junit.Test;import org.web3j.abi.FunctionEncoder;import org.web3j.abi.FunctionReturnDecoder;import org.web3j.abi.TypeReference;import org.web3j.abi.datatypes.*;import org.web3j.crypto.Credentials;import org.web3j.crypto.RawTransaction;import org.web3j.crypto.TransactionEncoder;import org.web3j.protocol.Web3j;import org.web3j.protocol.core.DefaultBlockParameterName;import org.web3j.protocol.core.methods.request.Transaction;import org.web3j.protocol.core.methods.response.EthGetTransactionCount;import org.web3j.protocol.http.HttpService;import org.web3j.tx.gas.DefaultGasProvider;import org.web3j.utils.Numeric;import java.math.BigInteger;import java.util.Arrays;import java.util.Collections;import java.util.List;public class We3jTest2 {public static String node = "https://rinkeby.infura.io/v3/7d00bf84530c4264969a4f0f231de8b6";Web3j web3j;Credentials credentials;{web3j = Web3j.build(new HttpService(node));credentials = Credentials.create("私钥");}public static final String contractAddress = "0xb19c13d0A37cDDE5c1F969a0d9BD6a50B3A11B4E";/*** 调用合约的只读方法，无需gas* @throws Exception*/@Testpublic void getName() throws Exception {Function function = new Function("getName",Collections.emptyList(),Arrays.asList(new TypeReference<Utf8String>(){}));String encodedFunction = FunctionEncoder.encode(function);org.web3j.protocol.core.methods.response.EthCall response = web3j.ethCall(Transaction.createEthCallTransaction(null, contractAddress, encodedFunction),DefaultBlockParameterName.LATEST).sendAsync().get();List<Type> results = FunctionReturnDecoder.decode(response.getValue(), function.getOutputParameters());Utf8String preValue = (Utf8String)results.get(0);System.out.println(preValue.getValue());}/*** 需要支付gas的方法* @throws Exception*/@Testpublic void setName() throws Exception {Function function = new Function("setName",Arrays.asList(new Utf8String("Tom")),Collections.emptyList());BigInteger nonce = getNonce(credentials.getAddress());String encodedFunction = FunctionEncoder.encode(function);BigInteger gasLimit = new BigInteger("300000");RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, DefaultGasProvider.GAS_PRICE,gasLimit, contractAddress, encodedFunction);org.web3j.protocol.core.methods.response.EthSendTransaction response =web3j.ethSendRawTransaction(Numeric.toHexString(TransactionEncoder.signMessage(rawTransaction, credentials))).sendAsync().get();String transactionHash = response.getTransactionHash();System.out.println(transactionHash);}/*** 需要支付gas和value的合约方法调用* @throws Exception*/@Testpublic void payETH() throws Exception {BigInteger nonce = getNonce(credentials.getAddress());Function function = new Function("payETH",Collections.EMPTY_LIST,Collections.EMPTY_LIST);String functionEncode = FunctionEncoder.encode(function);BigInteger value = new BigInteger("200");// 与不需要支付的value的方法调用，差别就在于多传一个eth数量的value参数RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, DefaultGasProvider.GAS_PRICE,DefaultGasProvider.GAS_LIMIT, contractAddress, value,functionEncode);org.web3j.protocol.core.methods.response.EthSendTransaction response =web3j.ethSendRawTransaction(Numeric.toHexString(TransactionEncoder.signMessage(rawTransaction, credentials))).sendAsync().get();String transactionHash = response.getTransactionHash();System.out.println(transactionHash);}private BigInteger getNonce(String address) throws Exception {EthGetTransactionCount ethGetTransactionCount =web3j.ethGetTransactionCount(address, DefaultBlockParameterName.LATEST).sendAsync().get();return ethGetTransactionCount.getTransactionCount();}}
总结
只读合约的调用的是call方法，这种方法无需私钥签名，只需要知道合约的地址和方法(方法名，入参、出参)即可。支付gas以及带value的调用，都是需要账户私钥的签名，分为三个步骤：encode(方法编码)、sign (对方法签名)、send(发送签名交易)。不管是js和java,调用流程都是一致的，本质上都是和以太坊节点通过json-rpc调用合约的etherscan地址
参考文档
web3.js 中文文档
web3j 英文文档
web3h 中文文档
上述内容如有错误欢迎留言讨论。
补充：
web3j 调用返回多个地址参数的类型
有小伙伴问我，合约返回的值是一个地址数组的情况怎么写。
如下，是我的一个例子
@Testpublic void callContractTransaction() throws Exception {Function function = new Function("getComponents",Collections.EMPTY_LIST,Arrays.asList(new TypeReference<DynamicArray<Address>>(){}));String encodedFunction = FunctionEncoder.encode(function);org.web3j.protocol.core.methods.response.EthCall response = web3j.ethCall(Transaction.createEthCallTransaction(null, contractAddress, encodedFunction),DefaultBlockParameterName.LATEST).sendAsync().get();Assert.isNull(response.getError(),"callContractTransaction error");List<Type> results = FunctionReturnDecoder.decode(response.getValue(), function.getOutputParameters());for (Type result : results) {System.out.println(result.getValue());}}
