How To Perform Ethereum Transactions In Spring Boot Application

What is an Ethereum Transaction?

The transaction is the way of interacting with the Ethereum network. The transaction is the information of our particular request we make on the Ethereum network. It gets stored in a block of chain on the platform

Prerequisites

We need Java 8+, a basic understanding of blockchain, and a fully synced and connected application to the Ethereum main or test node according to requirements. We will be using ETH's main network, spring boot understanding, and IDE. Also, we will use SpringToolSuit, active internet service, your ethereum service URL(maybe localhost or your own server), and some ETHs in your ethereum wallet for testing.

Dependency

In Pom.xml, add web3j dependency below. We can use a different/latest version.

Maven:

Gradle:

compile ('org.web3j:core:3.0.2')

Create and add transaction to:-

public class TransactionDTO {

@NotBlank
private BigDecimal amountToBeSend;

@NotBlank
private Double walletBalance;

@NotBlank
private String sendToAddress;

@NotBlank
private Double fee;

@NotBlank
private Double networkFee;

}

Now, see the following example for performing a transaction:-

/**
* Auto imports if you are using any IDE like Spring Tool Suite, Eclipse.
*/

public class Transaction {

private Logger logger = LoggerFactory.getLogger(ETHWalletController.class);

@Value("${service.url}")//To be declared in application.properties file
private String serverurl;

private Callback txReceiptCallback;

private TransactionReceiptProcessor noOpReceiptProcessor;

private Web3j web3j;

private QueuingTransactionReceiptProcessor transactionReceiptProcessor;

@PostConstruct
public void init() {

       this.web3j = Web3j.build(new HttpService(serverurl));
       this.txReceiptCallback = new Callback() {
           @Override
           public void accept(TransactionReceipt transactionReceipt) {
           }

@Override
public void exception(Exception exception) {

               logger.info(exception.getMessage());
           }
       };
       this.transactionReceiptProcessor = new QueuingTransactionReceiptProcessor(web3j, txReceiptCallback, 10, 60000);
       this.noOpReceiptProcessor = new NoOpProcessor(web3j);
   }

public Boolean ethExternalTransaction(TransactionDTO transactionDTO,EthWallet ethWallet) {

       Web3j parity = Web3j.build(new HttpService(serverurl));
       try {
           String decrPwd = CryptoUtil.decrypt(ethWallet.getWalletPwd(), ethWallet.getWalletPwdKey());
           Credentials credentials = WalletUtils.loadCredentials(decrPwd,
                    ethWallet.getWalletJsonFile());

           BigInteger amount = parity
                   .ethGetBalance(credentials.getAddress(), DefaultBlockParameterName.fromString("latest")).send()
                   .getBalance();
           BigDecimal balance = new BigDecimal(amount);

           BigDecimal conversionRate = BigDecimal.valueOf(Long.valueOf("1000000000000000000"));
           BigDecimal balanceInEther = balance.divide(conversionRate, 8, RoundingMode.FLOOR);
           logger.info(" balance before txn {} amount {} " + balanceInEther,
                   transactionDTO.getAmountToBeSend());
           BigInteger gas = BigInteger.valueOf(70000);
           BigInteger gasprice = parity.ethGasPrice().send().getGasPrice();
           BigInteger txnFee = gas.multiply(gasprice);
           BigInteger xth = new BigInteger("1000000000000000000");
           BigDecimal v1 = new BigDecimal(xth);
           BigDecimal v2 = new BigDecimal(txnFee);
           BigDecimal txnFeeInEther = v2.divide(v1);
           BigDecimal transferAmount = txnFeeInEther.add(transactionDTO.getAmountToBeSend());
           if ((balanceInEther.compareTo(transferAmount)) == 1) {
               TransactionManager rtm = new RawTransactionManager(parity, credentials, ChainId.NONE,
                       noOpReceiptProcessor);
               Transfer ethTransfer = new Transfer(parity, rtm);
               TransactionReceipt transactionReceipt = ethTransfer.sendFunds(transactionDTO.getSendToAddress(),
                       outAppTransactionDTO.getAmountToBeSend().setScale(8, RoundingMode.HALF_UP), Convert.Unit.ETHER)
                       .send();
               if (Optional.ofNullable(transactionReceipt).isPresent()
                       && !StringUtils.isEmpty(transactionReceipt.getTransactionHash())) {
                   //to do
               } else {
                   //to do
               }
           } else {
                //To do
                }
       } catch (Exception ex) {
           //to do
       }
   }

}

Here, the conversion rate and gas price may vary from time to time. It is needed to be tracked from Etherscan gastracker. Our current ethereum transaction can be also tracked on etherscan.

In the above example, we have an EthWallet object which contains the password, secret key to decrypt wallet, JSON file, and other web3j library specific required values to load eth wallet and perform a transaction.

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