用Java实现区块链交易存证
该文章仅供自己后期项目参考
1、如何在Java中构建区块链的基本结构，包括区块的创建、交易的处理和验证等。
我先从最基础的区块结构开始思考。一个区块应该包含交易数据、时间戳、前一个区块的哈希值以及自身的哈希值。哈希值的计算需要使用加密算法，我决定采用SHA-256算法，因为它是区块链中常用的加密算法，能够保证数据的完整性和安全性。
2、接下来，我思考如何处理交易。交易应该包含交易ID、发送方地址、接收方地址、交易金额和交易时间戳等信息。为了确保交易的安全性，还需要对交易进行数字签名。数字签名可以使用Java的内置安全库来实现，这样可以保证只有交易的发送方能够生成有效的签名。
3、我还需要考虑如何验证交易的合法性。这包括验证交易的输入是否未被花费过，以及交易的输入和输出是否匹配。此外，还需要验证交易的数字签名是否有效，以确保交易是由合法的发送方发起的。
4、在思考过程中，我意识到需要一个区块链类来管理整个区块链。这个类应该能够添加新的区块，并且能够验证整个区块链的完整性。为了实现这一点，我需要一个方法来验证每个区块的哈希值是否正确，以及每个区块的前一个哈希值是否与前一个区块的哈希值匹配。虑如何处理交易的输入和输出。每个交易的输入应该指向一个未被花费的输出，而输出则表示交易的接收方和金额。为了实现这一点，我需要创建交易输入和输出的类，并在交易类中引用它们。
以下是一个简单的Java区块链交易存证实现：
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;public class Blockchain {private List<Block> chain = new ArrayList<>();private List<Transaction> pendingTransactions = new ArrayList<>();private int difficulty = 2;public Blockchain() {// 创建创世区块Block genesisBlock = new Block("Genesis Block", "0");genesisBlock.mineBlock(difficulty);chain.add(genesisBlock);}public void addTransaction(Transaction transaction) {pendingTransactions.add(transaction);}public void minePendingTransactions() {Block block = new Block(pendingTransactions, getLatestBlock().getHash());block.mineBlock(difficulty);chain.add(block);pendingTransactions = new ArrayList<>();}public Block getLatestBlock() {return chain.get(chain.size() - 1);}public boolean isChainValid() {for (int i = 1; i < chain.size(); i++) {Block currentBlock = chain.get(i);Block previousBlock = chain.get(i - 1);if (!currentBlock.getHash().equals(currentBlock.calculateHash())) {return false;}if (!previousBlock.getHash().equals(currentBlock.getPreviousHash())) {return false;}}return true;}public static void main(String[] args) {Blockchain blockchain = new Blockchain();// 创建交易Transaction transaction1 = new Transaction("Alice", "Bob", 100);Transaction transaction2 = new Transaction("Bob", "Charlie", 50);// 添加交易到区块链blockchain.addTransaction(transaction1);blockchain.addTransaction(transaction2);// 挖矿blockchain.minePendingTransactions();// 打印区块链for (Block block : blockchain.chain) {System.out.println("Block Hash: " + block.getHash());System.out.println("Previous Hash: " + block.getPreviousHash());System.out.println("Transactions: " + block.getTransactions());System.out.println();}// 验证区块链System.out.println("Is blockchain valid? " + blockchain.isChainValid());}
}class Block {private String hash;private String previousHash;private List<Transaction> transactions;private long timestamp;private int nonce;public Block(List<Transaction> transactions, String previousHash) {this.transactions = transactions;this.previousHash = previousHash;this.timestamp = System.currentTimeMillis();this.hash = calculateHash();}public String calculateHash() {return StringUtil.applySha256(previousHash +Long.toString(timestamp) +Integer.toString(nonce) +transactions.toString());}public void mineBlock(int difficulty) {String target = new String(new char[difficulty]).replace('\0', '0');while (!hash.substring(0, difficulty).equals(target)) {nonce++;hash = calculateHash();}System.out.println("Block mined: " + hash);}public String getHash() {return hash;}public String getPreviousHash() {return previousHash;}public List<Transaction> getTransactions() {return transactions;}
}class Transaction {private String id;private String sender;private String receiver;private double amount;private String transactionTime;public Transaction(String sender, String receiver, double amount) {this.sender = sender;this.receiver = receiver;this.amount = amount;this.transactionTime = Long.toString(System.currentTimeMillis());this.id = StringUtil.applySha256(sender + receiver + amount + transactionTime);}@Overridepublic String toString() {return "Transaction{" +"id='" + id + '\'' +", sender='" + sender + '\'' +", receiver='" + receiver + '\'' +", amount=" + amount +", transactionTime='" + transactionTime + '\'' +'}';}
}class StringUtil {public static String applySha256(String input) {try {MessageDigest digest = MessageDigest.getInstance("SHA-256");byte[] hash = digest.digest(input.getBytes("UTF-8"));StringBuilder hexString = new StringBuilder();for (byte b : hash) {String hex = Integer.toHexString(0xff & b);if (hex.length() == 1) hexString.append('0');hexString.append(hex);}return hexString.toString();} catch (Exception e) {throw new RuntimeException(e);}}
}
这个实现包括了以下功能：
1、区块链的基本结构，包括区块和交易。
2、交易的创建和添加到区块链。
3、区块的挖矿过程，包括工作量证明（Proof of Work）。
4、区块链的验证，确保区块链的完整性和安全性。