Part One: Developing Your Own Blockchain
Here we present a series on how to develop your own blockchain in Java using Tomcat and Servlet. Creating your own blockchain from scratch is an exciting journey into the world of decentralized technology and cryptographic security. Whether you are an experienced developer or a curious beginner, building a blockchain allows you to grasp the core principles that power cryptocurrencies like Bitcoin and Ethereum. This guide is Part One of a series dedicated to helping you develop your blockchain, focusing on the fundamental elements and classes you'll need in your Java-based project.
Before we dive into the Java classes necessary for developing a blockchain, I recommend checking out this comprehensive step-by-step guide on how to create a cryptocurrency. It provides valuable insights and a solid foundation to start your journey.
Key Java Classes for Your Blockchain
To develop a blockchain, you need to implement several key classes that handle various aspects of the blockchain's functionality. Below is a brief overview of each class and its role in the system:
1. Block
The Block class represents a single block in the blockchain. Each block contains a list of transactions, a timestamp, a reference to the previous block, and a unique hash. Here's a simple structure for the Block class:
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
public class Block {
private static final long serialVersionUID = 1L;
private int id;
private int nonce;
private long timeStamp;
private String hash;
private String previousHash;
private ArrayList<TransactionNode> transactions=new ArrayList<TransactionNode>();
// Constructor and other methods
}
2. Blockchain
The Blockchain class manages the chain of blocks. It includes methods for adding new blocks, validating the chain, and ensuring that each block links correctly to the previous one.
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
public class BlockChain implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private List<Block> blockChain;
private Map<String,TransactionOutput> UTXOs;
// Methods for adding blocks, validating the chain, etc.
}
3. BlockchainFileOperation
This class handles the reading and writing of blockchain data to and from files, ensuring the persistence of the blockchain.
import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Base64;
import java.util.List;
import java.util.StringTokenizer;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
public class BlockchainFileOperation {
//https://crunchify.com/how-to-write-json-object-to-file-in-java/
private String directory = "c:/tmp";
4. Constants
The Constants class holds important constants such as the difficulty level for mining, the reward for mining a block, and other configuration parameters.
public class Constants {
public static final int DIFFICULTY=4;
public static final double MINER_REWARD=10;
public static final String
GENESIS_PREV_HASH="0000000000000000000000000000000000000000000000000000000000000000";
public static final double fee=0.01;
public Constants() {
}
}
5. CryptographyHelper
This utility class provides methods for cryptographic operations like generating hashes and digital signatures.
public class CryptographyHelper {
// Methods for hashing, generating key pairs, signing data, etc.
}
6. KeyPairHero
This class manages the generation and handling of public-private key pairs used in transactions.
import java.io.Serializable;
import com.starkbank.ellipticcurve.PrivateKey;
import com.starkbank.ellipticcurve.PublicKey;
public class KeyPairHero implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private PrivateKey privateKey = new PrivateKey();
PublicKey publicKey = privateKey.publicKey();
public PrivateKey getPrivateKey() {
return privateKey;
}
public void setPrivateKey(PrivateKey privateKey) {
this.privateKey = privateKey;
}
public PublicKey getPublicKey() {
return publicKey;
}
public void setPublicKey(PublicKey publicKey) {
this.publicKey = publicKey;
}
}
7. Miner
The Miner class is responsible for mining new blocks by solving the cryptographic puzzle defined by the difficulty level.
public class Miner {
private double reward;
public double getReward() {
return this.reward;
}
public void mine(Block block, BlockChain blockChain) {
// POW
// it takes some times to find the valid hash
while (!isGoldenHash(block)) {
block.incrementNonce();
block.generateHash();
}
System.out.println(block + " hash just mined...");
System.out.println("Hash is: " + block.getHash());
// Broadcasting it to the network
blockChain.addBlock(block);
reward += Constants.MINER_REWARD;
}
private boolean isGoldenHash(Block block) {
System.out.println("BLOCK ->"+block.getHash());
String leadingZeros = new String(new char[Constants.DIFFICULTY]).replace('\0', '0');
return block.getHash().substring(0, Constants.DIFFICULTY).equals(leadingZeros);
// return false;
}
}
8. ReceiveBlockServlet
This servlet class handles the receipt of new blocks from other nodes in the network, ensuring the blockchain stays updated across all participants.
import java.util.ArrayList;
@WebServlet("/receiveBlock")
public class ReceiveBlockServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private BlockChain blockchain;
private ArrayList<TransactionNode> unconfirmedTransactions = new ArrayList<TransactionNode>();
private Wallet wallet = new Wallet();
}
9. Sha256Helper
A utility class dedicated to SHA-256 hashing, which is crucial for creating block hashes.
import java.security.MessageDigest;
public class SHA256Helper {
public static String generateHash(String data) {
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(data.getBytes("UTF-8"));
StringBuffer hexadecimalString = new StringBuffer();
for (int i=0;i<hash.length;i++) {
String hexadecimal = Integer.toHexString(0xff&hash[i]);
if (hexadecimal.length()==1) hexadecimalString.append("0");
hexadecimalString.append(hexadecimal);
}
return hexadecimalString.toString();
}
catch(Exception e) {
throw new RuntimeException(e);
}
}
}
10. TransactionInput
This class represents an input in a transaction, referencing a previous transaction output.
public class TransactionInput implements Serializable{
private static final long serialVersionUID = 1L;
//every input has an output. This id is the transactionId of the TransactionOutput
private String transactionOutputId;
//this is the unspent transaction output
private TransactionOutput UTXO;
private double amount;
private String sendTo;
}
11. TransactionNode
A class that defines the structure of a transaction node within the network.
public class TransactionNode implements Serializable {
private static final long serialVersionUID = 1L;
private String transactionId;
private PrivateKey senderPrivateKey;
private PublicKey sender;
private PublicKey receiver;
private String receiverString; // to
private String senderString; // from
private double amount;
private Signature signature;
private String time;
// every transaction has inputs and outputs
public TransactionInput inputs;
public TransactionOutput outputs;
}
12. TransactionOutput
This class represents the output of a transaction, specifying the recipient and the amount transferred.
public class TransactionOutput implements Serializable{
private static final long serialVersionUID = 1L;
//identifier of the transaction output
private String id;
//transaction id of the parent (so the transaction it was created in)
private String parentTransactionId;
//the new owner of the coin
private PublicKey receiver;
private String receiverString;
private String senderString;
}
13. TransactionServlet
A servlet for handling incoming transactions from clients and processing them within the blockchain.
@WebServlet("/transaction")
public class TransactionServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private ArrayList<TransactionNode> unconfirmedTransactions = new ArrayList<TransactionNode>();
// Methods for processing transactions
}
Conclusion
Developing your blockchain involves creating a variety of interconnected classes, each handling a specific aspect of the blockchain's functionality. By breaking down the system into manageable components, you can focus on building and testing each part independently.
In the next part of this series, we will dive deeper into implementing these classes and see how they interact to form a functional blockchain. Stay tuned and happy coding!
For a detailed step-by-step guide on creating a cryptocurrency, don't forget to visit this link. It will provide you with the necessary groundwork to embark on this exciting journey.
Feel free to leave your comments and questions below, and let's build something amazing together!