区块链代码

pom文件：

	
		
			junit
			junit
			3.8.1
			test
		

		
			com.google.code.gson
			gson
			2.8.2
		

		
		
			commons-codec
			commons-codec
			1.9
		
	

测试类：

package indi.laf.blockchain;

/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
    	BlockChain bc=new BlockChain();
    	for (int i = 0; i < 5; i++) {
			bc.append(i+"");
		}
    	bc.print();
    	
    	//挖矿
    	bc.mineBlock(5);
    }
}

区块类：

package indi.laf.blockchain;

public class Block {

	/** 是这个块在整个链中的位置 */
	private int index;

	/** 显而易见就是块生成时的时间戳 */
	private String timestamp;

	/** 我们要记录的数据 */
	private String data;

	/** 是这个块通过 SHA256 算法生成的散列值 */
	private String hash;

	/** 指向前一个块的 SHA256 散列值 */
	private String prevHash;
	
	//工作量（挖的次数）
	private int nonce;

	public int getIndex() {
		return index;
	}

	public void setIndex(int index) {
		this.index = index;
	}

	public String getTimestamp() {
		return timestamp;
	}

	public void setTimestamp(String timestamp) {
		this.timestamp = timestamp;
	}

	public String getData() {
		return data;
	}

	public void setData(String data) {
		this.data = data;
	}

	public String getHash() {
		return hash;
	}

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

	public String getPrevHash() {
		return prevHash;
	}

	public void setPrevHash(String prevHash) {
		this.prevHash = prevHash;
	}

	public int getNonce() {
		return nonce;
	}

	public void setNonce(int nonce) {
		this.nonce = nonce;
	}
	
}

区块链类：

package indi.laf.blockchain;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;

import org.apache.commons.codec.digest.DigestUtils;

import com.google.gson.Gson;

public class BlockChain {
	ArrayList bc = new ArrayList();
	Gson gs=new Gson();

	public String calculateHash(Block block) {
		String record = block.getNonce()+block.getIndex() + block.getTimestamp() + (block.getData()) + block.getPrevHash();
		return DigestUtils.sha256Hex(record);
	}

	// 生成一个区块
	public Block generateBlock(String data) {
		Block newBlock = new Block();
		newBlock.setIndex(bc.size());
		newBlock.setTimestamp(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));
		newBlock.setData(data);
		newBlock.setPrevHash(bc.size() == 0 ? "" : bc.get(bc.size() - 1).getHash());
		newBlock.setHash(calculateHash(newBlock));
		return newBlock;
	}

	// 校验
	public boolean isBlockValid(Block newBlock) {
		int lastIndex = newBlock.getIndex() - 1;

		// 第一个的情况
		if (lastIndex == -1) {
			return true;
		}

		Block oldBlock = bc.get(lastIndex);
		if (oldBlock.getIndex() != newBlock.getIndex() - 1) {
			return false;
		}

		if (!oldBlock.getHash().equals(newBlock.getPrevHash())) {
			return false;
		}

		if (!calculateHash(newBlock).equals(newBlock.getHash())) {
			return false;
		}
		return true;
	}

	public void append(String data) {
		Block newBlock = generateBlock(data);
		if (isBlockValid(newBlock)) {
			bc.add(newBlock);
		}
	}

	// 过期的链切换成最新的链
	public void replaceChain(ArrayList newBlocks) {
		if (newBlocks.size() > bc.size()) {
			bc = newBlocks;
		}
	}

	//挖矿
	public void mineBlock(int difficulty) {
		Block block = bc.get(bc.size()-1);
		String target = new String(new char[difficulty]).replace('\0', '0');
		while (!block.getHash().substring(0, difficulty).equals(target)) {
			block.setNonce(block.getNonce()+1);
			block.setHash(calculateHash(block));
		}
		System.out.println("挖到矿了!!!" + block.getHash()+"，挖了"+block.getNonce()+"次");
	}
	
	//遍历打印
	public void print() {
		for (Block block : bc) {
			System.out.println(gs.toJson(block));
		}
	}
}