Deploy smart contracts using web3j java library

Question

I am using web3j java library to deploy a smart contract.

// I am encoding the constructor parameters here -- 2 & 3, 10 & 20
String encodedConstructor =
         FunctionEncoder.encodeConstructor(Arrays.asList(new Type(value), ...));

RawTransaction rawTransaction = RawTransaction.createContractTransaction(
    <nonce>,
    <gasPrice>,
    <gasLimit>,
    <value>,
    "0x <compiled smart contract code>" + encodedConstructor);

byte[] signedMessage = TransactionEncoder.signMessage(rawTransaction, <credentials>);

String hexValue = Numeric.toHexString(signedMessage);

I am using

web3.eth.sendRawTransaction(hexValue) 

to deploy the contract.

My smart contract has a constructor which accepts some parameters(a, b) and it has a function sum which returns sum of a and b. After deployment if I call the sum function, it always returns me 0.

Need help.

Reference Link: https://docs.web3j.io/transactions.html#creation-of-a-smart-contract

Answer 1

you need to create a Function Object for your smart contract constructor then in data field were you put compiled solidity add the decode result of this function 'compiled smart contract'+'decoded function of the constructor'

Answer 2

I have to pass the required parameters in Web3J datatypes, link on github.

A simple example is given in the a test file, FunctionEncoderTest.java.

 ArrayList<Type> dataParams = new ArrayList<>();    
 dataParams.add(new Utf8String("Name"));
 dataParams.add(new Address("Ethereum Address"));

 //This will be used for creating "RawTransaction" object
 Function function = new Function("updateDetails", dataParams, Collections.<TypeReference<?>>emptyList());