区块链demo之Java版

Block.java

import java.util.Date;

public class Block {
    
    public String hash;
    public String previousHash; 
    private String data; //our data will be a simple message.
    private long timeStamp; //as number of milliseconds since 1/1/1970.
    private int nonce;
    
    //Block Constructor.  
    public Block(String data,String previousHash ) {
        this.data = data;
        this.previousHash = previousHash;
        this.timeStamp = new Date().getTime();
        
        this.hash = calculateHash(); //Making sure we do this after we set the other values.
    }
    
    //Calculate new hash based on blocks contents
    public String calculateHash() {
        String calculatedhash = StringUtil.applySha256( 
                previousHash +
                Long.toString(timeStamp) +
                Integer.toString(nonce) + 
                data 
                );
        return calculatedhash;
    }
    
    //Increases nonce value until hash target is reached.
    public void mineBlock(int difficulty) {
        String target = StringUtil.getDificultyString(difficulty); //Create a string with difficulty * "0" 
        while(!hash.substring( 0, difficulty).equals(target)) {
            nonce ++;
            hash = calculateHash();
        }
        System.out.println("Block Mined!!! : " + hash);
    }
    
}

NoobChain.java

import java.util.ArrayList;
import com.google.gson.GsonBuilder;

public class NoobChain {
    
    public static ArrayList<Block> blockchain = new ArrayList<Block>();
    public static int difficulty = 5;

    public static void main(String[] args) {    
        //add our blocks to the blockchain ArrayList:
        
        System.out.println("Trying to Mine block 1... ");
        addBlock(new Block("Hi im the first block", "0"));
        
        System.out.println("Trying to Mine block 2... ");
        addBlock(new Block("Yo im the second block",blockchain.get(blockchain.size()-1).hash));
        
        System.out.println("Trying to Mine block 3... ");
        addBlock(new Block("Hey im the third block",blockchain.get(blockchain.size()-1).hash));    
        
        System.out.println("\nBlockchain is Valid: " + isChainValid());
        
        String blockchainJson = StringUtil.getJson(blockchain);
        System.out.println("\nThe block chain: ");
        System.out.println(blockchainJson);
    }
    
    public static Boolean isChainValid() {
        Block currentBlock; 
        Block previousBlock;
        String hashTarget = new String(new char[difficulty]).replace('\0', '0');
        
        //loop through blockchain to check hashes:
        for(int i=1; i < blockchain.size(); i++) {
            currentBlock = blockchain.get(i);
            previousBlock = blockchain.get(i-1);
            //compare registered hash and calculated hash:
            if(!currentBlock.hash.equals(currentBlock.calculateHash()) ){
                System.out.println("Current Hashes not equal");            
                return false;
            }
            //compare previous hash and registered previous hash
            if(!previousBlock.hash.equals(currentBlock.previousHash) ) {
                System.out.println("Previous Hashes not equal");
                return false;
            }
            //check if hash is solved
            if(!currentBlock.hash.substring( 0, difficulty).equals(hashTarget)) {
                System.out.println("This block hasn't been mined");
                return false;
            }
            
        }
        return true;
    }
    
    public static void addBlock(Block newBlock) {
        newBlock.mineBlock(difficulty);
        blockchain.add(newBlock);
    }
}

StringUtil.java

import java.security.MessageDigest;

import com.google.gson.GsonBuilder;

public class StringUtil {
    
    //Applies Sha256 to a string and returns the result. 
    public static String applySha256(String input){
        
        try {
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            
            //Applies sha256 to our input, 
            byte[] hash = digest.digest(input.getBytes("UTF-8"));
            
            StringBuffer hexString = new StringBuffer(); // This will contain hash as hexidecimal
            for (int i = 0; i < hash.length; i++) {
                String hex = Integer.toHexString(0xff & hash[i]);
                if(hex.length() == 1) hexString.append('0');
                hexString.append(hex);
            }
            return hexString.toString();
        }
        catch(Exception e) {
            throw new RuntimeException(e);
        }
    }
    
    //Short hand helper to turn Object into a json string
    public static String getJson(Object o) {
        return new GsonBuilder().setPrettyPrinting().create().toJson(o);
    }
    
    //Returns difficulty string target, to compare to hash. eg difficulty of 5 will return "00000"  
    public static String getDificultyString(int difficulty) {
        return new String(new char[difficulty]).replace('\0', '0');
    }
    
    
}