Java Web3j Ethereum Transfer Guide: Basic and Token Transactions

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Blockchain development has become increasingly accessible thanks to powerful libraries like Web3j, a lightweight Java library for integrating Ethereum blockchain functionality into Java-based applications. Whether you're building decentralized finance (DeFi) tools, NFT platforms, or enterprise blockchain solutions, understanding how to perform basic ETH transfers and ERC-20 token transactions using Web3j is essential.

This comprehensive guide walks you through setting up Web3j in a Maven project, executing secure Ethereum transfers, and sending custom tokens—complete with practical code examples and best practices. We’ll also answer common questions developers face when working with Web3j.

Setting Up Web3j in a Maven Project

Before performing any blockchain operations, you need to integrate Web3j into your Java environment. If you're using Apache Maven, simply add the Web3j core dependency to your pom.xml file.

<dependency>
    <groupId>org.web3j</groupId>
    <artifactId>core</artifactId>
    <version>3.4.0</version>
</dependency>

This dependency provides all necessary tools for connecting to Ethereum nodes, managing cryptographic keys, signing transactions, and interacting with smart contracts.

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Performing a Basic ETH Transfer

Transferring Ether (ETH) from one address to another is one of the most fundamental operations in Ethereum development. Web3j simplifies this process with its Transfer utility class.

Here’s a step-by-step implementation:

public static void transfer() throws Exception {
    // Connect to an Ethereum node via Infura or your own RPC endpoint
    Web3j web3j = Web3j.build(new HttpService("infura节点链接"));

    // Import private key (ensure it's securely stored!)
    BigInteger privateKey = new BigInteger("钱包私钥", 16);
    ECKeyPair ecKeyPair = ECKeyPair.create(privateKey);
    Credentials credentials = Credentials.create(ecKeyPair);

    // Send 0.001 ETH to the recipient address
    TransactionReceipt transactionReceipt = Transfer.sendFunds(
        web3j,
        credentials,
        "目标地址",
        BigDecimal.valueOf(0.001),
        Convert.Unit.ETHER
    ).send();

    // Output transaction result
    System.out.println(transactionReceipt);
}

Key Points:

Executing ERC-20 Token Transfers

Unlike ETH, tokens such as USDT, DAI, or custom ERC-20 tokens require interaction with their respective smart contracts. This involves manually constructing a transaction that calls the transfer function on the token contract.

Below is a complete method for sending ERC-20 tokens:

public static void transferToken() throws Exception {
    Web3j web3j = Web3j.build(new HttpService("infura节点链接"));

    BigInteger privateKey = new BigInteger("私钥", 16);
    ECKeyPair ecKeyPair = ECKeyPair.create(privateKey);
    Credentials credentials = Credentials.create(ecKeyPair);

    String fromAddress = credentials.getAddress();

    // Get current nonce to prevent transaction replay
    EthGetTransactionCount ethGetTransactionCount = web3j.ethGetTransactionCount(
        fromAddress,
        DefaultBlockParameterName.LATEST
    ).sendAsync().get();

    BigInteger nonce = ethGetTransactionCount.getTransactionCount();

    // Define recipient and transfer value (in wei)
    Address toAddress = new Address("目标地址");
    Uint256 value = new Uint256(new BigInteger("数量 单位wei"));

    List<Type> parametersList = new ArrayList<>();
    parametersList.add(toAddress);
    parametersList.add(value);

    List<TypeReference<?>> outList = new ArrayList<>();

    // Create function call: transfer(address,uint256)
    Function function = new Function("transfer", parametersList, outList);
    String encodedFunction = FunctionEncoder.encode(function);

    // Set gas parameters
    System.out.println("Gas Price: " + DefaultGasProvider.GAS_PRICE);
    System.out.println("Gas Limit: " + DefaultGasProvider.GAS_LIMIT);

    // Build raw transaction
    RawTransaction rawTransaction = RawTransaction.createTransaction(
        nonce,
        DefaultGasProvider.GAS_PRICE,
        new BigInteger("210000"), // Adjust gas limit based on contract complexity
        "合约地址", // ERC-20 contract address
        encodedFunction
    );

    // Sign transaction
    byte[] signedMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
    String hexValue = Numeric.toHexString(signedMessage);

    // Broadcast transaction
    EthSendTransaction ethSendTransaction = web3j.ethSendRawTransaction(hexValue).sendAsync().get();
    Object transactionHash = ethSendTransaction.getTransactionHash();

    System.out.println("Transaction Hash: " + transactionHash.toString());
}

Important Notes:

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Frequently Asked Questions (FAQ)

Q: Is Web3j suitable for production environments?

Yes, Web3j is widely used in enterprise-grade blockchain applications. It supports asynchronous calls, robust error handling, and integration with Spring Boot, making it ideal for scalable systems.

Q: Can I use local Ethereum nodes instead of Infura?

Absolutely. While Infura offers convenient cloud-based access, you can connect Web3j to any Ethereum node (e.g., Geth, Parity) by pointing the HttpService to your local RPC URL (http://localhost:8545).

Q: How do I handle transaction failures or reverts?

Always check the TransactionReceipt. If getStatus().equals("0x1"), the transaction succeeded. A status of "0x0" indicates failure. Additionally, monitor gas limits and simulate transactions off-chain when possible.

Q: What security best practices should I follow when handling private keys?

Never hardcode private keys. Use secure vaults like Hashicorp Vault, environment variables, or hardware security modules (HSMs). Also, enable two-factor authentication and restrict access permissions in production.

Q: How can I verify if a token transfer was successful?

After obtaining the transaction hash, use web3j.ethGetTransactionReceipt() to fetch the receipt. Check the logs for Transfer events emitted by the ERC-20 contract.

Q: Does Web3j support other blockchains besides Ethereum?

Yes. Web3j works with any Ethereum-compatible blockchain such as Binance Smart Chain, Polygon, Avalanche, and Arbitrum—just adjust the node URL accordingly.

Final Thoughts

Mastering Web3j for Java-based Ethereum interactions opens doors to innovative blockchain integrations. From simple ETH transfers to complex smart contract invocations, Web3j provides a clean, object-oriented API that fits seamlessly into modern Java ecosystems.

As blockchain adoption grows across industries—from finance to supply chain—developers equipped with skills in programmatic token transfers, secure key management, and transaction broadcasting will remain in high demand.

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