转账

    fun sendEthTransaction(
        privateKey: String,
        toAddress: String,
        amount: BigDecimal
    ) {
    	//chainId
        val chainId:Long = 1
        //url 可以从https://chainlist.org/里面获取可用节点
        //eth转账，bnb同理，但需发送到bnb对应节点
        val url = "https://xxx"
        val web3j = Web3j.build(HttpService(url))
        val credentials = Credentials.create(privateKey)
        val count =
            web3j.ethGetTransactionCount(credentials.address, DefaultBlockParameterName.LATEST)
                .send()
        val nonce = count.transactionCount
        val gasPrice = Convert.toWei("20", Convert.Unit.GWEI).toBigInteger()
        val gasLimit = BigInteger.valueOf(21000)
        val value = Convert.toWei(amount, Convert.Unit.ETHER).toBigInteger()
        val rawTransaction = RawTransaction.createEtherTransaction(
            nonce, gasPrice, gasLimit, toAddress, value
        )
        val signedMessage = TransactionEncoder.signMessage(rawTransaction, chainId,credentials)
        val hexValue = Numeric.toHexString(signedMessage)
        logDebug("签名后的数据 $hexValue")
        val ethSendTransaction = web3j.ethSendRawTransaction(hexValue).send()
        if (ethSendTransaction.hasError()) {
            println("发送 ETH 交易时出错: ${ethSendTransaction.error.message}")
        } else {
            println("ETH 交易哈希: ${ethSendTransaction.transactionHash}")
        }

    }

    fun sendErc20USDTTransaction(
        privateKey: String,
        toAddress: String,
        amount: BigInteger
    ) {
        //erc20 usdt 合约地址
        val contractAddress = "0xdAC17F958D2ee523a2206206994597C13D831ec7"
        val url = "https://xxx"
        val web3j = Web3j.build(HttpService(url))
        val credentials = Credentials.create(privateKey)

        val count = web3j.ethGetTransactionCount(
            credentials.address, DefaultBlockParameterName.LATEST
        ).send()
        val nonce = count.transactionCount
        val gasPrice = Convert.toWei("20", Convert.Unit.GWEI).toBigInteger()
        val gasLimit = BigInteger.valueOf(200000)

        val function = Function(
            "transfer",
            listOf(Address(toAddress), Uint256(amount)),
            emptyList()
        )
        val data = FunctionEncoder.encode(function)

        val rawTransaction = RawTransaction.createTransaction(
            nonce, gasPrice, gasLimit, contractAddress, data
        )

        val signedMessage = TransactionEncoder.signMessage(rawTransaction, credentials)
        val hexValue = Numeric.toHexString(signedMessage)

        val ethSendTransaction = web3j.ethSendRawTransaction(hexValue).send()
        if (ethSendTransaction.hasError()) {
            println("发送 ERC - 20 代币交易时出错: ${ethSendTransaction.error.message}")
        } else {
            println("ERC - 20 代币交易哈希: ${ethSendTransaction.transactionHash}")
        }

    }

更多：
https://chainlist.org/