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标题: 【上海校区】区块链-java入门Demo [打印本页]

作者: 梦缠绕的时候 时间: 2018-7-3 09:58
标题: 【上海校区】区块链-java入门Demo
本帖最后由梦缠绕的时候于 2018-7-3 09:59 编辑

正在创建第一个区块链.......
创建区块:00000d3c0681cd67f8050ab996e1400f99c0060ba4cb22d0c07685d9ae50cd10
正在创建第二个区块链.......
创建区块:00000eafdd53bed5586d480d7704169c45b25fcb0bc5846b16be6fbeee88ec69
正在创建第三个区块链.......
创建区块:00000a6391f185b143bfccf571ef660204f945f43cb4101e804b360d06c9af66
区块链是否有效的: true
[
{
"hash": "00000d3c0681cd67f8050ab996e1400f99c0060ba4cb22d0c07685d9ae50cd10",
"previousHash": "0",
"data": "我是第一个区块链",
"timeStamp": 1528268281634,
"nonce": 7033501
},
{
"hash": "00000eafdd53bed5586d480d7704169c45b25fcb0bc5846b16be6fbeee88ec69",
"previousHash": "00000d3c0681cd67f8050ab996e1400f99c0060ba4cb22d0c07685d9ae50cd10",
"data": "我是第二个区块链",
"timeStamp": 1528268301568,
"nonce": 340676
},
{
"hash": "00000a6391f185b143bfccf571ef660204f945f43cb4101e804b360d06c9af66",
"previousHash": "00000eafdd53bed5586d480d7704169c45b25fcb0bc5846b16be6fbeee88ec69",
"data": "我是第三个区块链",
"timeStamp": 1528268302664,
"nonce": 319404
}
]
Process finished with exit code 0

1.Block

package com.block;
import java.util.Date;
/**
* @Author: cxx
* 封装区块对象
* @Date: 2018/6/6 14:45
*/
public class Block {
public String hash;
//上一个区块的hash值
public String previousHash;
//每个区块存放的信息，这里我们存放的是一串字符串
private String data;
//时间戳
private long timeStamp;
//挖矿者的工作量证明
private int nonce;
//构造
public Block(String data,String previousHash ) {
this.data = data;
this.previousHash = previousHash;
this.timeStamp = new Date().getTime();
//根据previousHash、data和timeStamp产生唯一hash
this.hash = calculateHash();
}
//基于上一块的内容计算新的散列
public String calculateHash() {
String calculatedhash = StringUtil.applySha256(
previousHash +
Long.toString(timeStamp) +
Integer.toString(nonce) +
data
);
return calculatedhash;
}
//挖矿
public void mineBlock(int difficulty) {
//目标值，difficulty越大，下面计算量越大
String target = StringUtil.getDificultyString(difficulty);
//difficulty如果为5，那么target则为 00000
while(!hash.substring( 0, difficulty).equals(target)) {
nonce ++;
hash = calculateHash();
}
System.out.println("创建区块:" + hash);
}
}

2.StringUtil

package com.block;
import java.security.MessageDigest;
import com.google.gson.GsonBuilder;
/**
* 工具类
* 创建数字签名、返回JSON格式数据、返回难度字符串目标
* @author pibigstar
*
*/
public class StringUtil {
//将Sha256应用到一个字符串并返回结果
public static String applySha256(String input){
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(input.getBytes("UTF-8"));
StringBuffer hexString = new StringBuffer();
for (int i = 0; i < hash.length; i++) {
String hex = Integer.toHexString(0xff & hash);
if(hex.length() == 1) hexString.append('0');
hexString.append(hex);
}
return hexString.toString();
}
catch(Exception e) {
throw new RuntimeException(e);
}
}
//返回JSON格式数据
public static String getJson(Object o) {
return new GsonBuilder().setPrettyPrinting().create().toJson(o);
}
//返回难度字符串目标，与散列比较。难度5将返回“00000”
public static String getDificultyString(int difficulty) {
return new String(new char[difficulty]).replace('\0', '0');
}
public static void main(String[] args) {
System.out.println(getDificultyString(5));
}
}

3.BlockChain

package com.block;
import java.util.ArrayList;
import com.google.gson.GsonBuilder;
/**
* 创建区块链
* @author pibigstar
*
*/
public class BlockChain{
//存放所有的区块集合
public static ArrayList<Block> blockchain = new ArrayList<Block>();
public static int difficulty = 5;//挖矿的难度，数字越大越难
public static void main(String[] args) {
System.out.println("正在创建第一个区块链....... ");
addBlock(new Block("我是第一个区块链", "0"));//创世块
System.out.println("正在创建第二个区块链....... ");
addBlock(new Block("我是第二个区块链",blockchain.get(blockchain.size()-1).hash));
System.out.println("正在创建第三个区块链.......");
addBlock(new Block("我是第三个区块链",blockchain.get(blockchain.size()-1).hash));
System.out.println("区块链是否有效的: " + isChainValid());
String blockchainJson = StringUtil.getJson(blockchain);
System.out.println(blockchainJson);
}
/**
* 检查区块链的完整性
* @return
*/
public static Boolean isChainValid() {
Block currentBlock;
Block previousBlock;
String hashTarget = new String(new char[difficulty]).replace('\0', '0');
//循环区块链检查散列:
for(int i=1; i < blockchain.size(); i++) {
currentBlock = blockchain.get(i);
previousBlock = blockchain.get(i-1);
//比较注册散列和计算散列:
if(!currentBlock.hash.equals(currentBlock.calculateHash()) ){
System.out.println("Current Hashes not equal");
return false;
}
//比较以前的散列和注册的先前的散列
if(!previousBlock.hash.equals(currentBlock.previousHash) ) {
System.out.println("Previous Hashes not equal");
return false;
}
//检查哈希是否被使用
if(!currentBlock.hash.substring( 0, difficulty).equals(hashTarget)) {
System.out.println("这个区块还没有被开采。。。");
return false;
}
}
return true;
}
/**
* 增加一个新的区块
* @param newBlock
*/
public static void addBlock(Block newBlock) {
newBlock.mineBlock(difficulty);
blockchain.add(newBlock);
}
}

作者: 吴琼老师 时间: 2018-7-5 17:42

作者: 不二晨 时间: 2018-7-12 17:00
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作者: wuqiong 时间: 2018-7-12 18:07

作者: 摩西摩西OvO 时间: 2018-7-26 10:38

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