首先，我们要有自己的智能合约，我们使用测试网络（ropsten），还要有自己开发编号。申请如下：
地址：https://infura.io/
注册登录，创建自己的项目
注意：选择测试ropsten链，复制自己的链接 web3j需要用到。
第二步：使用solidity编译自己的智能合约（个人理解就是链上的服务器脚本），为了案例的丰富性和实用性，全方位的展示web3j调度性，我们使用留言版智能合约模板，solidity代码如下（采用了8.15编译）：
// SPDX-License-Identifier: MITpragma solidity ^0.8.0;//声明一个结构体用于留言保持struct Message{ string word; address from; string timeStr;}contract Test_Web3j{ Message[] public AllMsg; //构造方法 constructor (){ } //接受留言 function setWord(string memory sendMsgStr,string memory tStr)public returns(uint256){ AllMsg.push(Message({word:sendMsgStr,from:msg.sender,timeStr:tStr})); return AllMsg.length; } //查询留言 function getWord() public view returns(uint256,string memory,address,string memory){ if(AllMsg.length==0){ //当没有留言数据时候，返回空 return (0,"",address(0),""); }else{ //当有留言时候，返回最新的一条 uint256 indexInt=AllMsg.length-1; Message storage thisMsg=AllMsg[indexInt]; return (AllMsg.length,thisMsg.word,thisMsg.from,thisMsg.timeStr); } } //返回总留言的条数 function getSize() public view returns(uint256){ return AllMsg.length; } //测试方法1 function testStr() public pure returns(string memory){ return "hello word"; } function testInt(uint256 argInt) public pure returns(uint256){ return argInt+10; }}采用remix在线版发布合约，注意浏览器中需要安装metaMask；才需要ropsten有测试币
第三步 java部分
import java.math.BigInteger;import java.util.Arrays;import java.util.List;import org.web3j.abi.FunctionEncoder;import org.web3j.abi.FunctionReturnDecoder;import org.web3j.abi.datatypes.Function;import org.web3j.abi.datatypes.Utf8String;import org.web3j.abi.datatypes.Address;import org.web3j.abi.datatypes.generated.Uint256;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.EthCall;import org.web3j.protocol.core.methods.response.EthGetBalance;import org.web3j.protocol.core.methods.response.EthSendTransaction;import org.web3j.protocol.http.HttpService;import org.web3j.abi.datatypes.Type;import org.web3j.abi.TypeReference;import org.web3j.tx.Contract;import org.web3j.utils.Convert;import org.web3j.utils.Numeric;public class mainCreateSolitidyJava { public static void main(String[] args) { try { String url = "https://ropsten.infura.io/v3/8ac1e3ea********7a4a077c0a0745"; String contractAddress="0x954e9A986467861********F5aEa8b83cAB63B6"; //合约地址 String fromAddr="0xb4377fb04FE5aDe3C35*******0cd354308807bF"; //查询用户地址 String inputPrivateKey="4369ceac05601**************a29f2ab6a41e7c6f93f3ea55222c5d"; //该账号密钥 //查询一下自己虚拟币的数量 Web3j web3j = Web3j.build(new HttpService(url)); //第二个参数：区块的参数，建议选最新区块 EthGetBalance balance = web3j.ethGetBalance(fromAddr, DefaultBlockParameterName.LATEST).send(); String blanceETH = Convert.fromWei(balance.getBalance().toString(), Convert.Unit.ETHER).toPlainString();//.concat(" ether"); System.out.println("====> 拥有的以太坊币 :" + blanceETH); //测试调用方法一 try { List input = Arrays.asList(); //输入参数 List output = Arrays.asList(new TypeReference<Utf8String>() {}); //接受返回参数 String methodName = "testStr"; Function function = new Function(methodName, input, output); String data = FunctionEncoder.encode(function); Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data); EthCall ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get(); List<Type> results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters()); System.out.println("==111==>"+results.get(0).getValue()); }catch (Exception e){ e.printStackTrace(); } //测试调用方法二 try { List input = Arrays.asList(new Uint256(100)); List output = Arrays.asList(new TypeReference<Uint256>() {}); String methodName = "testInt"; Function function = new Function(methodName, input, output); String data = FunctionEncoder.encode(function); Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data); EthCall ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get(); List<Type> results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters()); System.out.println("==222==>"+results.get(0).getValue()); }catch (Exception e){ e.printStackTrace(); } //测试调用方法三 try { List input = Arrays.asList(new Utf8String("第一条留言"),new Utf8String("这是插入时间")); List output = Arrays.asList(new TypeReference<Uint256>() {}); String methodName = "setWord"; Function function = new Function(methodName, input, output); String encodedFunction = FunctionEncoder.encode(function); BigInteger nonce =NormalUtil.getNonce(web3j,fromAddr); //获取nonce BigInteger gasPrice = NormalUtil.requestCurrentGasPrice(web3j); //gas数 BigInteger gasLimit = Contract.GAS_LIMIT; //限制gas数 RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, gasPrice, gasLimit, contractAddress, encodedFunction); Credentials credentials = Credentials.create(inputPrivateKey); byte[] signMessage = TransactionEncoder.signMessage(rawTransaction, credentials); String hexValue = Numeric.toHexString(signMessage); EthSendTransaction ethResult=web3j.ethSendRawTransaction(hexValue).sendAsync().get(); System.out.println("交易编号："+ethResult.getTransactionHash()); }catch (Exception e){ e.printStackTrace(); } //获得总留言数量 try { List input = Arrays.asList(); List ouput = Arrays.asList(new TypeReference<Uint256>() {}); String methodName = "getSize"; Function function = new Function(methodName, input, ouput); String data = FunctionEncoder.encode(function); Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data); EthCall ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get(); List<Type> results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters()); System.out.println("==333==>"+results.get(0).getValue()); }catch (Exception e){ e.printStackTrace(); } //调用自己合约地址 try { List input = Arrays.asList(); List ouput = Arrays.asList(new TypeReference<Uint256>(){},new TypeReference<Utf8String>() {},new TypeReference<Address>() {},new TypeReference<Utf8String>() {}); String methodName = "getWord"; Function function = new Function(methodName, input, ouput); String data = FunctionEncoder.encode(function); Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data); EthCall ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get(); //System.out.println(ethCall.getValue()); List<Type> results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters()); System.out.println("==444==>"+results.get(1).getValue()); }catch (Exception e){ e.printStackTrace(); } }catch (Exception e){ e.printStackTrace(); } }}Java部分核心难度地方：ethCall和ethSendRawTransaction区别，ethcall调用的方法是不需要gas费用，而ethSendRawTransaction需要，因此此教程中，插入留言就需要使用ethSendRawTransaction方法来调用。
运行结果如下：
