Ethereum: How do I sign and send a raw transaction using BitcoinJ?

Signing and Sending a Raw Transaction use BitcoinJ

In this article, we’ll have a process of creating a raw transactition on the Ethereum blockchain use the BitcoinJ library. We’ll cover how to sign and send a raw transaction from scratch.

Prerequisites*

Before ou start, make of the comment you has:

BitcoinJ (the offical Java implementation of the Bitcoin protocol)

A Bitcoin Client (optional but recommended for debugging purposes)

Creating a Raw Transaction

Ethereum: How do I sign and send a raw transaction using BitcoinJ?

A raw transaction is a plain text string that represses the contens of a block. To this one, we need to follow thees steps:

Create a new transaction

: We’ll use Transaction class BitcoinJ to crate a new transaction.

Initiation the unpents list: We’ll of all splen coins in this.

Code*

`java



Transaction transaction = new Transaction(params);

// 遍历未芹列表，组装合适的item

double sub = 0;

String address = null;

List unspens = new ArrayList<>();

Map splenCoins = new HashMap<>();

// ...

params.getUnspent().forEach((unspent: Unspent) -> { {

    if (unspent.isFunded()) {

        double amount = unspent.getAmount();

        suum += amauunt;

        SpentCoins.put(new Coin(unspent.getHash(), 1), unpent);

    }

});

double totalAmount = sub - SpentCoins.values()stream()

        .mapToDoouble(Unspent::getAmount).sum();

traansaction.setFromAddress(address);

tranceToAddress("0x..."); // Replant wth your recipient's eddress

transaction.addTransactionDetails (totalAmount, "raw transaction details");



Key Points*


Weterate over the unspen and add any coins that are funded to yourspentCoinsmap.

We calculate the total amount in the raw transaction by subtracting

We set the sender's to address to a fixed value ("0x...") and add details to the raw transaction, including its total.



Signing the Raw Transaction


To sign the raw transaction use BitcoinJ, we'll create a newSignerinstance:

java

Signer signer = new Signer(transaction);



We can one that signer to generalate a signature for transaction:

java



by[] signature = signer.signRawTransaction(transaction);



Sending the Raw Transaction


To send the transaction, we'll create aTransactionSenderinstance:

java

TransactionSender sender = new TransactionSender(transaction, null); +



We can one thing that sender to broadcast

java



sender.broadcast();



Note that in practic, you'd likely want to set to a recipient for the requiss for the transaction when creatying it. The example above shows how to do that.

Example Use Case

To send a raw transaction from scratch use BitcoinJ, follow thees:

Create a newTransaction` instance and initial the unspen.

Iterate over the unspen and add any funded coins to a map.

Calculate the total amount splend in the raw transaction.

Set the sender’s of the eddress and addais about the raw transaction.

Sign the raw transaction uses a signer.

Send the signed raw transactition.

This way is your a rud-starting point for creating raw transactions on the Ethereum blockchain uning BitcoinJ. Remember to replace placeholder addresses with your yourwn recipient’s information!

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