[Ethereum] How to make transaction using private key and address using web3j

go-ethereumjavaraw-transactiontransactionsweb3j

I have a private key and address . Is it possible to make transaction with these parameter using web3j.

Best Answer

Web3j web3j = Web3j.build(new HttpService(""));
    Credentials credentials = Credentials.create("privateKey");
    BigInteger nonce = web3j.ethGetTransactionCount(credentials.getAddress(), DefaultBlockParameterName.PENDING).sendAsync().get().getTransactionCount();
    BigInteger gasPrice = web3j.ethGasPrice().sendAsync().get().getGasPrice();
    RawTransaction rawTransaction = RawTransaction.createEtherTransaction(nonce, gasPrice, Constants.ETH_GAS_LIMIT, "address", Convert.toWei("amount", Convert.Unit.ETHER).toBigIntegerExact());
    EthSendTransaction response = web3j.ethSendRawTransaction(Numeric.toHexString(TransactionEncoder.signMessage(rawTransaction, credentials))).send();
    String hash = response.getTransactionHash();

Related Solutions

Web3j – Using Web3j to Load a Smart Contract and Specify Credentials

To generate the Credentials if you have a plain public key and private key, you need to convert them in to the hex representation and then pass them in to the constructor for Credentials

String hexPrivateKey = String.format("%040x", new BigInteger(1, privateKey.getBytes()));
String hexPublicKey = String.format("%040x", new BigInteger(1, publicKey.getBytes()));  
Credentials creds = Credentials.create(hexPrivateKey, hexPublicKey);

Where publicKey and privateKey are Strings containing your plain pub and priv keys

Web3j Key Generation – How to Generate Private Key and Address Using Web3j

Below is my approach, verified by importing the result privatekey into MetaMask and get the same address as expected.

private static JSONObject process(String seed){

         JSONObject processJson = new JSONObject();

         try {
            ECKeyPair ecKeyPair = Keys.createEcKeyPair();
            BigInteger privateKeyInDec = ecKeyPair.getPrivateKey();

            String sPrivatekeyInHex = privateKeyInDec.toString(16);

            WalletFile aWallet = Wallet.createLight(seed, ecKeyPair);
            String sAddress = aWallet.getAddress();


            processJson.put("address", "0x" + sAddress);
            processJson.put("privatekey", sPrivatekeyInHex);


        } catch (CipherException e) {
            //
        } catch (InvalidAlgorithmParameterException e) {
            //
        } catch (NoSuchAlgorithmException e) {
            //
        } catch (NoSuchProviderException e) {
            //
        } 

        return processJson;
}


main(){  // unit test 
    String seed = UUID.randomUUID().toString();
    JSONObject result = process(seed); // get a json containing private key and address
}

Best Answer

Related Solutions

Web3j – Using Web3j to Load a Smart Contract and Specify Credentials

Web3j Key Generation – How to Generate Private Key and Address Using Web3j

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