Java Tools and Libraries for Blockchain Development: A Beginner’s Guide

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Java, one of the most popular and mature programming languages, has increasingly found a place in the world of blockchain development. While languages like Solidity are essential for writing smart contracts, Java plays a vital role in integrating blockchain features into applications, building backends, and even interacting directly with blockchain nodes.

In this guide, we’ll introduce three widely used Java libraries for blockchain development:

• Web3j – for working with Ethereum

• EthereumJ – an Ethereum implementation in Java

• BitcoinJ – for building Bitcoin-based applications

We’ll also walk through simple code examples to demonstrate how these tools work.

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1. Web3j: Java Library for Ethereum

Web3j is a lightweight Java library for integrating with Ethereum nodes. It allows you to interact with smart contracts and send transactions directly from Java applications.

✅ Key Features:

• Communicate with Ethereum nodes via JSON-RPC

• Deploy and interact with smart contracts

• Create and send transactions

• Wallet management

🔧 Setup:

Add the following to your Maven pom.xml:

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>4.10.0</version>
</dependency>

🧪 Example: Connect to an Ethereum node and get the balance of an address

import org.web3j.protocol.Web3j;
import org.web3j.protocol.http.HttpService;
import org.web3j.protocol.core.methods.response.Web3ClientVersion;
import org.web3j.protocol.core.methods.response.EthGetBalance;
import org.web3j.utils.Convert;

import java.math.BigDecimal;
import java.math.BigInteger;

public class Web3jExample {
    public static void main(String[] args) throws Exception {
        Web3j web3 = Web3j.build(new HttpService("https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID"));

        Web3ClientVersion clientVersion = web3.web3ClientVersion().send();
        System.out.println("Connected to: " + clientVersion.getWeb3ClientVersion());

        EthGetBalance balance = web3.ethGetBalance("0xde0B295669a9FD93d5F28D9Ec85E40f4cb697BAe", 
                                                   org.web3j.protocol.core.DefaultBlockParameterName.LATEST)
                                   .send();
        BigInteger wei = balance.getBalance();
        BigDecimal ether = Convert.fromWei(wei.toString(), Convert.Unit.ETHER);
        System.out.println("Balance: " + ether + " ETH");
    }
}

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2. EthereumJ: Java Implementation of Ethereum

EthereumJ is a full Ethereum node written in Java. Unlike Web3j, which connects to existing nodes, EthereumJ lets you build and run your own Ethereum node or simulate Ethereum network behavior locally.

✅ Key Features:

• Implements Ethereum protocol

• Useful for simulations and academic research

• Full control of Ethereum internals

⚠️ Note:

EthereumJ is powerful but lower-level and harder to use than Web3j. It's mainly for developers interested in running or modifying Ethereum clients.

🧪 Example: Start EthereumJ Node

import org.ethereum.facade.EthereumFactory;
import org.ethereum.facade.Ethereum;

public class EthereumJExample {
    public static void main(String[] args) {
        Ethereum ethereum = EthereumFactory.createEthereum();
        System.out.println("Ethereum node started.");
    }
}

This will start a local Ethereum node with default configuration. You can modify settings (like enabling mining) using a custom config file.

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3. BitcoinJ: Java Library for Bitcoin

BitcoinJ is a Java-based library for working with the Bitcoin protocol. It allows you to create wallets, send/receive transactions, and even connect to the Bitcoin network without running a full node.

✅ Key Features:

• SPV (Simplified Payment Verification) node support

• Create and manage Bitcoin wallets

• Send and receive Bitcoin

• Monitor blockchain events

🔧 Setup:

Add to pom.xml:

<dependency>
  <groupId>org.bitcoinj</groupId>
  <artifactId>bitcoinj-core</artifactId>
  <version>0.16.1</version>
</dependency>

🧪 Example: Create a Bitcoin Wallet and Display Balance

import org.bitcoinj.core.NetworkParameters;
import org.bitcoinj.core.Wallet;
import org.bitcoinj.kits.WalletAppKit;
import org.bitcoinj.params.TestNet3Params;

import java.io.File;

public class BitcoinJExample {
    public static void main(String[] args) {
        NetworkParameters params = TestNet3Params.get();
        WalletAppKit kit = new WalletAppKit(params, new File("."), "wallet-example");

        kit.startAsync();
        kit.awaitRunning();

        Wallet wallet = kit.wallet();
        System.out.println("Wallet address: " + wallet.currentReceiveAddress());
        System.out.println("Wallet balance: " + wallet.getBalance().toFriendlyString());
    }
}

This example runs on Bitcoin Testnet (not real BTC), making it great for development.

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✅ Conclusion

Java offers a solid foundation for blockchain development through powerful libraries:

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