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撰寫（費用委託）

當您要執行智能合約時，您可以向 feepayer 發送**"交易 "，其中包括支付請求**。

從 Web3j 和 kaia 庫（web3j-ext）中導入必要的類。

使用 Web3j 連接到 kaia 區塊鏈並指定 URL

使用私鑰創建發送方和付費方證書。

指定已部署合約的**地址

確定交易的gas價格和gas限額

從 credentials.getAddress() 獲取發件人地址

獲取發件人地址的 nonce

從 Kaia 網絡獲取鏈 ID

為交易參數初始化變量

創建gas供應商，並設定靜態gas價格和gas限額

使用聯繫地址、Web3j 實例、憑據和gas提供商加載合約。 您可以通過該實例讀寫合約

在寫入之前，獲取合約中存儲的當前數字

為調用方法 setNumber 設置合約參數

將交易類型定義為 FEE_DELEGATED_SMART_CONTRACT_EXECUTION

創建原始交易

使用 "KlayTransactionEncoder.signMessage "以**發送方的身份簽署交易。

使用 "KlayTransactionEncoder.signMessageAsFeePayer "將交易簽署為付費方。

向 kaia 網絡發送已簽署的交易

短暫延遲以確保交易完成

寫入後，獲取存儲在合約中的更新號

關閉 Web3j 實例

WriteContractWithFeeDelegationExample.java

package org.web3j.example.contracts;

import java.io.IOException;

import java.math.BigInteger;

import org.web3j.crypto.KlayCredentials;

import org.web3j.crypto.KlayRawTransaction;

import org.web3j.crypto.KlayTransactionEncoder;

import org.web3j.crypto.transaction.type.TxType;

import org.web3j.crypto.transaction.type.TxTypeFeeDelegatedSmartContractExecution;

import org.web3j.crypto.transaction.type.TxType.Type;

import org.web3j.tx.response.PollingTransactionReceiptProcessor;

import org.web3j.tx.response.TransactionReceiptProcessor;

import org.web3j.example.keySample;

import org.web3j.protocol.core.DefaultBlockParameterName;

import org.web3j.protocol.core.methods.request.Transaction;

import org.web3j.protocol.core.methods.response.EthChainId;

import org.web3j.protocol.core.methods.response.EthSendTransaction;

import org.web3j.protocol.http.HttpService;

import org.web3j.protocol.kaia.Web3j;

import org.web3j.utils.Numeric;

import org.web3j.protocol.kaia.core.method.response.KlayCallResponse;

import org.web3j.protocol.kaia.core.method.response.TransactionReceipt;

import org.web3j.tx.gas.StaticGasProvider;

import org.web3j.abi.FunctionEncoder;

import org.web3j.abi.datatypes.Function;

import org.web3j.abi.datatypes.Uint;

import java.util.Arrays;

import java.util.Collections;

public class WriteContractWithFeeDelegationExample {

/**

* @throws Exception

*

*/

public static void run() throws Exception {

Web3j web3j = Web3j.build(new HttpService(keySample.BAOBAB_URL));

KlayCredentials credentials = KlayCredentials.create(keySample.LEGACY_KEY_privkey);

KlayCredentials credentials_feePayer = KlayCredentials.create(keySample.LEGACY_KEY_FEEPAYER_privkey);

String contractAddr = "0x95Be48607498109030592C08aDC9577c7C2dD505";

BigInteger GAS_PRICE = BigInteger.valueOf(50000000000L);

BigInteger GAS_LIMIT = BigInteger.valueOf(6721950);

String from = credentials.getAddress();

BigInteger nonce = web3j.ethGetTransactionCount(from, DefaultBlockParameterName.LATEST).send()

.getTransactionCount();

EthChainId EthchainId = web3j.ethChainId().send();

long chainId = EthchainId.getChainId().longValue();

BigInteger value = BigInteger.ZERO;

StaticGasProvider gasProvider = new StaticGasProvider(GAS_PRICE, GAS_LIMIT);

Counter counter = Counter.load(contractAddr, web3j, credentials.convertToCredentials(), gasProvider);

// Get number before Contract Write

System.out.println("number before : " + counter.number().send());

// Contract Write (Set number with setNumber function)

Function function = new Function("setNumber", // Function name

Arrays.asList(new Uint(BigInteger.valueOf(50))), // Function input parameters

Collections.emptyList()); // Function returned parameters

String txData = FunctionEncoder.encode(function);

byte[] payload = Numeric.hexStringToByteArray(txData);

TxType.Type type = Type.FEE_DELEGATED_SMART_CONTRACT_EXECUTION;

KlayRawTransaction raw = KlayRawTransaction.createTransaction(

type,

nonce,

GAS_PRICE,

GAS_LIMIT,

contractAddr,

value,

from,

payload);

// Sign as sender

byte[] signedMessage = KlayTransactionEncoder.signMessage(raw, chainId, credentials);

// Sign same message as Fee payer

signedMessage = KlayTransactionEncoder.signMessageAsFeePayer(raw, chainId, credentials_feePayer);

String hexValue = Numeric.toHexString(signedMessage);

web3j.ethSendRawTransaction(hexValue).send();

try {

Thread.sleep(2000);

} catch (Exception e) {

System.out.println(e);

}

// Get number after Contract Write

System.out.println("number after : " + counter.number().send());

web3j.shutdown();

}

}

output

❯ java WriteContractWithFeeDelegationExample.java

number before : 298

number after : 50