不知不覺陷虎，又到了周末，已經很久沒有寫東西了杠袱，最近看了很多關于區(qū)塊鏈的東西尚猿，但是簡易的入門的很少，于是楣富，我想著寫一篇能讓小白快速理解最基礎的代碼凿掂。
區(qū)塊鏈概述
網上有很多關于這方面的文章和歷史，這里有幾個問題簡單描述一下：
比特幣是一個分布式記賬系統(tǒng)纹蝴，既然是記賬庄萎，那么數(shù)據(jù)記在哪兒呢？答案是塘安，記在千千萬萬個網絡的節(jié)點上糠涛。
分布式記賬，要明白幾個問題：
一致性的問題兼犯？
多種原因可能造成不一致忍捡，比如
- 每臺機器的算力是不一樣的，計算有快有慢
- 當我和你都收到一筆交易A的時候切黔，我要記這一筆賬砸脊，你也要記，一切順利的情況下纬霞，我們都記成功了凌埂，賬本也都是一致的結果，那么如果由于網絡問題诗芜，你沒收到這一筆交易侨舆，怎么辦？
區(qū)塊鏈系統(tǒng)是這樣處理的绢陌，全網所有的機器都會有一個確認過程挨下，這個確認的過程就是校驗交易合法的過程，你遺失了這一筆交易A脐湾，最后你算出來的區(qū)塊和別人不一樣臭笆，你就白白付出了努力，結果不被認可！
共同造假的問題愁铺？
比特幣可不可能有造假的問題鹰霍？當然有，當全網參與記賬的節(jié)點有51%參與造假茵乱，記賬就是不對的茂洒，當前比特幣就有這樣的算力中心化的問題。
賬記在哪兒瓶竭？過程怎樣督勺？
用戶提交一筆交易到網絡，網絡各個礦工節(jié)點（參與記賬的）收到了這一筆交易斤贰，不會立即記賬智哀，而是把這筆交易標記到下一個區(qū)塊，當準備好出新的區(qū)塊的時候荧恍，礦工需要先算一道題算出一個值瓷叫，這個值是表示你經過千辛萬苦參與了這一次記賬，然后把區(qū)塊信息（包含交易信息送巡，上一個區(qū)塊的hash摹菠，proof算出的答案），提交到網絡骗爆，所有節(jié)點的礦工發(fā)現(xiàn)來了一個新的區(qū)塊次氨，立即停下算題的腳步，看一下這個區(qū)塊是不是工作在最長鏈淮腾，如果是糟需，校驗一下屉佳，如果成功谷朝，則確認。
proof瞎寫會怎樣武花？
接著上面的問題說圆凰，如果我沒有算這個題，直接瞎寫一個答案体箕，提交出去专钉，別的礦工看了，校驗了一把累铅，發(fā)現(xiàn)你是扯淡的跃须，你算出來的這個區(qū)塊就丟掉，永遠不會被確認娃兽。
代碼實現(xiàn)：
扯淡了那么久菇民，還是開始寫一段代碼，更直觀。
Block定義
package com.xingchuan.study.blockchain.domain;
import java.util.Set;
/**
* @author xingchuan.qxc
* @since 2018/1/20
*/
public class Block {
/**
* 區(qū)塊的序號
*/
private Long index;
/**
* 區(qū)塊產生的時間
*/
private Long timestamp;
/**
* 區(qū)塊對應哪些交易
*/
private Set<Transaction> transactions;
/**
* 工作證明
*/
private Long proof;
/**
* 上一個區(qū)塊的hash
*/
private String previousHash;
public Long getIndex() {
return index;
}
public void setIndex(Long index) {
this.index = index;
}
public Long getTimestamp() {
return timestamp;
}
public void setTimestamp(Long timestamp) {
this.timestamp = timestamp;
}
public Set<Transaction> getTransactions() {
return transactions;
}
public void setTransactions(Set<Transaction> transactions) {
this.transactions = transactions;
}
public Long getProof() {
return proof;
}
public void setProof(Long proof) {
this.proof = proof;
}
public String getPreviousHash() {
return previousHash;
}
public void setPreviousHash(String previousHash) {
this.previousHash = previousHash;
}
@Override
public String toString() {
return "{\"Block\":{"
+ " \"index\":\"" + index + "\""
+ ", \"timestamp\":\"" + timestamp + "\""
+ ", \"transactions\":" + transactions
+ ", \"proof\":\"" + proof + "\""
+ ", \"previousHash\":\"" + previousHash + "\""
+ "}}";
}
}
Transaction定義
/**
* @author xingchuan.qxc
* @since 2018/1/20
*/
public class Transaction {
/**
* 發(fā)送人
*/
private String sender;
/**
* 接收人
*/
private String recipient;
/**
* 金額
*/
private long amount;
public String getSender() {
return sender;
}
public void setSender(String sender) {
this.sender = sender;
}
public String getRecipient() {
return recipient;
}
public void setRecipient(String recipient) {
this.recipient = recipient;
}
public long getAmount() {
return amount;
}
public void setAmount(long amount) {
this.amount = amount;
}
@Override
public String toString() {
return "{\"Transaction\":{"
+ " \"sender\":\"" + sender + "\""
+ ", \"recipient\":\"" + recipient + "\""
+ ", \"amount\":\"" + amount + "\""
+ "}}";
}
}
Blockchain定義
/**
* @author xingchuan.qxc
* @since 2018/1/20
*/
public class Blockchain {
/**
* Block 鏈
*/
private List<Block> blockchain = new LinkedList<>();
/**
* 待生成Block的交易
*/
private Set<Transaction> transactions = new HashSet<>();
/**
* 初始化的時候第练，創(chuàng)建genesis block
* @throws NoSuchAlgorithmException
*/
public Blockchain() throws NoSuchAlgorithmException {
//genesis block阔馋，真實場景下，應該是同步區(qū)塊鏈的最長鏈最后一個區(qū)塊
newBlock(720L);
}
/**
* 挖礦產生新的區(qū)塊
* @throws NoSuchAlgorithmException
*/
public void mine() throws NoSuchAlgorithmException {
Block lastBlock = blockchain.get(blockchain.size() - 1);
Long lastProof = lastBlock.getProof();
Long proof = proofOfWork(lastProof);
newTransaction("0", "mineNode", 1L);
newBlock(proof);
}
/**
* 計算工作證明
* @param lastProof
* @return
* @throws NoSuchAlgorithmException
*/
public Long proofOfWork(Long lastProof) throws NoSuchAlgorithmException {
Long proof = 0L;
while (!validProof(lastProof, proof)) {
proof++;
}
return proof;
}
/**
* 算題娇掏，這里定義為呕寝，直到算出來的值以0000開頭，才算正確答案
* @param lastProof
* @param proof
* @return
* @throws NoSuchAlgorithmException
*/
private boolean validProof(Long lastProof, Long proof) throws NoSuchAlgorithmException {
String guess = "" + lastProof + proof;
String guessHash = hash(guess);
return guessHash.startsWith("0000");
}
/**
* 新建一個區(qū)塊
* @param proof
* @return
* @throws NoSuchAlgorithmException
*/
public Block newBlock(Long proof) throws NoSuchAlgorithmException {
Set<Transaction> transactions = new HashSet<>();
transactions.addAll(this.transactions);
int index = blockchain.size() - 1;
Block lastBlock = null;
if (index >= 0) {
lastBlock = blockchain.get(index);
}
if (lastBlock == null) {
lastBlock = new Block();
}
Block block = new Block();
block.setIndex(Long.valueOf(blockchain.size() + 1));
block.setTimestamp(System.currentTimeMillis());
block.setTransactions(transactions);
block.setProof(proof);
block.setPreviousHash(hash(lastBlock.toString()));
blockchain.add(block);
this.transactions.clear();
return block;
}
/**
* 提交一筆新的交易
* @param sender
* @param recipient
* @param amount
* @return
*/
public long newTransaction(String sender, String recipient, Long amount) {
Transaction transaction = new Transaction();
transaction.setSender(sender);
transaction.setRecipient(recipient);
transaction.setAmount(amount);
this.transactions.add(transaction);
int lastBlockIndex = blockchain.size() - 1;
if (lastBlockIndex >= 0) {
Block block = blockchain.get(lastBlockIndex);
return block.getIndex() + 1;
}
return 0;
}
/**
* SHA-512 算工作量證明
* @param value
* @return
* @throws NoSuchAlgorithmException
*/
private static String hash(String value) throws NoSuchAlgorithmException {
MessageDigest messageDigest = MessageDigest.getInstance("SHA-512");
messageDigest.update(value.getBytes());
return bytesToHexString(messageDigest.digest());
}
private static String bytesToHexString(byte[] src) {
StringBuilder stringBuilder = new StringBuilder();
if (src == null || src.length <= 0) {
return null;
}
for (int i = 0; i < src.length; i++) {
int v = src[i] & 0xFF;
String hv = Integer.toHexString(v);
if (hv.length() < 2) {
stringBuilder.append(0);
}
stringBuilder.append(hv);
}
return stringBuilder.toString();
}
public List<Block> getBlockchain() {
return blockchain;
}
public Set<Transaction> getTransactions() {
return transactions;
}
}
測試代碼
/**
* @author xingchuan.qxc
* @since 2018/1/20
*/
public class TestBlockChain {
public static void main(String[] args) throws Exception {
//初始化
Blockchain blockchain = new Blockchain();
//提交一筆交易
blockchain.newTransaction("xingchuan", "shine", 7201L);
//挖礦記錄這一筆交易
blockchain.mine();
List<Block> blockList = blockchain.getBlockchain();
blockList.forEach(block->{
System.out.println(block);
});
Set<Transaction> transactions = blockchain.getTransactions();
for (Transaction transaction : transactions) {
System.out.println(transaction);
}
}
}
運行結果：
測試運行結果
