简简单单区块链

difficulty可以改成8

package org.example;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;

class Block {
    private int index;
    private long timestamp;
    private String data;
    private String previousHash;
    private String hash;
    private int nonce;

    public Block(int index, long timestamp, String data, String previousHash) {
        this.index = index;
        this.timestamp = timestamp;
        this.data = data;
        this.previousHash = previousHash;
        this.nonce = 0;
        this.hash = calculateHash();
    }

    public String calculateHash() {
        try {
            String input = index + timestamp + data + previousHash + nonce;
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            byte[] hashBytes = digest.digest(input.getBytes());
            
            // 将字节数组转换为十六进制字符串
            StringBuilder hexString = new StringBuilder();
            for (byte b : hashBytes) {
                String hex = Integer.toHexString(0xff & b);
                if (hex.length() == 1) hexString.append('0');
                hexString.append(hex);
            }
            return hexString.toString();
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }

    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! Nonce: " + nonce + ", Hash: " + hash);
    }

    // Getters
    public int getIndex() { return index; }
    public long getTimestamp() { return timestamp; }
    public String getData() { return data; }
    public String getPreviousHash() { return previousHash; }
    public String getHash() { return hash; }
    public int getNonce() { return nonce; }

    @Override
    public String toString() {
        return "Block #" + index + 
               " [Hash: " + hash + 
               ", Prev: " + previousHash + 
               ", Nonce: " + nonce + 
               ", Data: " + data + "]";
    }

    public void setPreviousHash(String hash) {
        this.previousHash=hash;
    }
}

class Blockchain {
    private List<Block> chain;
    private int difficulty;

    public Blockchain(int difficulty) {
        this.chain = new ArrayList<>();
        this.difficulty = difficulty;
        createGenesisBlock();
    }

    private void createGenesisBlock() {
        Block genesisBlock = new Block(0, System.currentTimeMillis(), "Genesis Block", "0");
        chain.add(genesisBlock);
        System.out.println("Genesis Block created!");
    }

    public Block getLatestBlock() {
        return chain.get(chain.size() - 1);
    }

    public void addBlock(Block newBlock) {
        newBlock.setPreviousHash(getLatestBlock().getHash());
        newBlock.mineBlock(difficulty);
        chain.add(newBlock);
        System.out.println("Block #" + newBlock.getIndex() + " added to the blockchain!");
    }

    public boolean isChainValid() {
        for (int i = 1; i < chain.size(); i++) {
            Block currentBlock = chain.get(i);
            Block previousBlock = chain.get(i - 1);

            // 验证当前区块的哈希是否正确
            if (!currentBlock.getHash().equals(currentBlock.calculateHash())) {
                System.out.println("Block #" + currentBlock.getIndex() + " has invalid hash!");
                return false;
            }

            // 验证与前一个区块的链接
            if (!currentBlock.getPreviousHash().equals(previousBlock.getHash())) {
                System.out.println("Block #" + currentBlock.getIndex() + " has invalid previous hash!");
                return false;
            }

            // 验证工作量证明（难度要求）
            String target = new String(new char[difficulty]).replace('\0', '0');
            if (!currentBlock.getHash().substring(0, difficulty).equals(target)) {
                System.out.println("Block #" + currentBlock.getIndex() + " does not meet difficulty requirement!");
                return false;
            }
        }
        return true;
    }

    public void printChain() {
        System.out.println("\n===== Blockchain =====");
        for (Block block : chain) {
            System.out.println(block);
        }
        System.out.println("======================");
    }

    // 内部类扩展Block以添加setPreviousHash方法
    static class BlockExtended extends Block {
        public BlockExtended(int index, long timestamp, String data, String previousHash) {
            super(index, timestamp, data, previousHash);
        }

        public void setPreviousHash(String previousHash) {
            // 使用反射或其他方法设置，这里简化处理
            // 实际应用中可能需要修改Block类设计
            // 这里仅用于演示目的
            try {
                java.lang.reflect.Field field = Block.class.getDeclaredField("previousHash");
                field.setAccessible(true);
                field.set(this, previousHash);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

public class SimpleBlockchain {
    public static void main(String[] args) {
        // 创建难度为2的区块链
        Blockchain blockchain = new Blockchain(2);
        
        // 添加新区块
        Blockchain.BlockExtended block1 = new Blockchain.BlockExtended(
            1, 
            System.currentTimeMillis(), 
            "Transaction Data 1", 
            ""
        );
        blockchain.addBlock(block1);
        
        Blockchain.BlockExtended block2 = new Blockchain.BlockExtended(
            2, 
            System.currentTimeMillis(), 
            "Transaction Data 2", 
            ""
        );
        blockchain.addBlock(block2);
        
        // 打印区块链
        blockchain.printChain();
        
        // 验证区块链
        System.out.println("\nIs blockchain valid? " + blockchain.isChainValid());
        
        // 尝试篡改数据
        System.out.println("\nAttempting to tamper with Block 1 data...");
        // 注意：实际应用中需要更安全的数据访问方式
        // 这里仅用于演示篡改检测
        Block blockToTamper = blockchain.getLatestBlock(); // 获取最后一个区块
        try {
            java.lang.reflect.Field dataField = Block.class.getDeclaredField("data");
            dataField.setAccessible(true);
            dataField.set(blockToTamper, "Tampered Data");
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        // 再次验证区块链
        System.out.println("Is blockchain valid after tampering? " + blockchain.isChainValid());
    }
}

1. ​​Block 类​​：

   • 表示区块链中的单个区块

   • 包含索引、时间戳、数据、前一个区块的哈希、当前哈希和随机数（nonce）

   • calculateHash()方法使用 SHA-256 算法计算区块哈希

   • mineBlock()方法实现工作量证明（挖矿）过程

2. ​​Blockchain 类​​：

   • 管理整个区块链

   • createGenesisBlock()创建创世区块（第一个区块）

   • addBlock()添加新区块并执行挖矿

   • isChainValid()验证区块链的完整性

   • printChain()打印整个区块链

3. ​​BlockExtended 内部类​​：

   • 扩展 Block 类以添加设置前一个哈希的方法

   • 实际应用中可能需要修改 Block 类设计

4. ​​SimpleBlockchain 主类​​：

   • 演示区块链的创建、添加区块和验证过程

   • 包含篡改检测演示

程序功能：

1. 创建创世区块

2. 添加新区块并执行工作量证明（挖矿）

3. 打印整个区块链

4. 验证区块链完整性

5. 演示篡改检测