以ERC20转账为例

token转账参数即data字段
String methodName = "transfer";
List<Type> inputParameters = new ArrayList<>();
List<TypeReference<?>> outputParameters = new ArrayList<>();
Address tAddress = new Address(toAddress);
Uint256 tokenValue = new Uint256(BigDecimal.valueOf(amount).multiply(BigDecimal.TEN.pow(decimals)).toBigInteger());
inputParameters.add(tAddress);
inputParameters.add(tokenValue);
TypeReference<Bool> typeReference = new TypeReference<Bool>() {
};
outputParameters.add(typeReference);
Function function = new Function(methodName, inputParameters, outputParameters);
String data = FunctionEncoder.encode(function);

第二种 利用web3j生成的contract类去调用交易

TokenERC20 contract = TokenERC20.load(contractAddress, web3j, credentials,
Convert.toWei("10", Convert.Unit.GWEI).toBigInteger(),
BigInteger.valueOf(100000));
String myAddress = null;
String toAddress = null;
BigInteger amount = BigInteger.ONE;
try {
TransactionReceipt receipt = contract.transfer(toAddress, amount).send();
} catch (Exception e) {
e.printStackTrace();
}

eth转账及普通转账
BigInteger nonce;
EthGetTransactionCount ethGetTransactionCount = null;
try {
ethGetTransactionCount =
getClient()
.ethGetTransactionCount(fromAddress, DefaultBlockParameterName.LATEST).send();
} catch (Exception e) {
e.printStackTrace();
}
if (ethGetTransactionCount == null) return null;
nonce = ethGetTransactionCount.getTransactionCount();
BigInteger gasPrice = Convert.toWei(gas, Convert.Unit.GWEI).toBigInteger();
BigInteger value = Convert.toWei(balance, Convert.Unit.ETHER).toBigInteger();
String data = "";
byte chainId = ChainId.NONE; // 测试网络

然后ERC20及eth使用 该data发送签名交易即可

RawTransaction rawTransaction = RawTransaction.createTransaction(
nonce,
gasPrice,
gasLimit,
to,
value,
data);
ECKeyPair ecKeyPair = ECKeyPair.create(new BigInteger(privateKey, 16));
Credentials credentials = Credentials.create(ecKeyPair);
byte[] signedMessage = TransactionEncoder.signMessage(rawTransaction, credentials;
String hexValue = Numeric.toHexString(signedMessage);
EthSendTransaction ethSendTransaction = web3j.ethSendRawTransaction(signedData).send();
System.out.println(ethSendTransaction.getTransactionHash());