web3j的基础用法-5合约的调用（持续完善中...）

web3j调用智能合约是web3j使用的关键，当前区块链的核心

其实原理很简单

https://github.com/OpenZeppelin/openzeppelin-contracts
这是智能合约优秀的框架，经过了无数安全的效验，目前绝大多数项目引用此相关依赖。
有些函数是固定写法例如claim，deposit，approve等等。

目前web3j使用org.web3j.abi.datatypes.Function , org.web3j.abi.TypeReference,两个核心类将智能合约的方法和参数构造，再通过org.web3j.abi.FunctionEncoder，FunctionEncoder.encode()格式化后Transaction指令就可以了。

package com.we3j.demo.wallet;

import org.web3j.abi.FunctionEncoder;
import org.web3j.abi.FunctionReturnDecoder;
import org.web3j.abi.datatypes.generated.Uint256;
import org.web3j.protocol.Web3j;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.*;
import org.web3j.protocol.core.DefaultBlockParameterName;
import org.web3j.protocol.core.methods.request.Transaction;
import org.web3j.protocol.core.methods.response.EthCall;

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutionException;

/**
 * @Author jambestwick
 * @create 2021/12/5 0005  21:04
 * @email [email protected]
 * 

 * ERC20的代币
 */
public class TokenClient {

    private static String emptyAddress = "0x0000000000000000000000000000000000000000";

    /**
     * 查询代币发行总量
     *
     * @param web3j
     * @param contractAddress
     * @return
     */
    public static BigInteger getTokenTotalSupply(Web3j web3j, String contractAddress) {
        if (web3j == null) return null;
        String methodName = "totalSupply";
        String fromAddr = emptyAddress;
        BigInteger totalSupply = BigInteger.ZERO;
        List<Type> inputParameters = new ArrayList<>();
        List<TypeReference<?>> outputParameters = new ArrayList<>();

        TypeReference<Uint256> typeReference = new TypeReference<Uint256>() {
        };
        outputParameters.add(typeReference);

        Function function = new Function(methodName, inputParameters, outputParameters);

        String data = FunctionEncoder.encode(function);
        Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data);

        EthCall ethCall;
        try {
            ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get();
            List<Type> results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters());
            totalSupply = (BigInteger) results.get(0).getValue();
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        return totalSupply;
    }


    /****
     * 调用claim方法抢NFT Token
     * ***/
    public static boolean claimNFT(Web3j web3j, String contractAddress, Integer tokenId) {
        if (web3j == null) return false;
        String methodName = "claim";
        String fromAddr = emptyAddress;
        Function function = new Function(
                methodName,
                Arrays.asList(new Uint256(tokenId)),
                Arrays.asList(new TypeReference<Type>() {
                }));

        String data = FunctionEncoder.encode(function);
        Transaction transaction = Transaction.createEthCallTransaction(fromAddr, contractAddress, data);

        EthCall ethCall;
        try {
            ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).sendAsync().get();
            //List results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters());
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        return true;
    }


}

我么以查看Loot的总供应量为例，演示一遍。Loot合约地址：0xff9c1b15b16263c61d017ee9f65c50e4ae0113d7

总数7779与ethscan一致，Ok。

项目github地址
https://github.com/jambestwick/we3jdemo