package com.weihua.blockchains.blackchain;
import java.util.Date;
public class BlockMan {
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 BlockMan(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); }
}
package com.weihua.blockchains.blackchain;
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'); }
}
package com.weihua.blockchains.blackchain;
import java.util.ArrayList;
public class TestBlockChain {
public static ArrayList<BlockMan> blockchain = new ArrayList<BlockMan>(); 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 BlockMan("Hi im the first block", "0")); System.out.println("Trying to Mine block 2... "); addBlock(new BlockMan("Yo im the second block",blockchain.get(blockchain.size()-1).hash)); System.out.println("Trying to Mine block 3... "); addBlock(new BlockMan("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() { BlockMan currentBlock; BlockMan 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(BlockMan newBlock) { newBlock.mineBlock(difficulty); blockchain.add(newBlock); }
}
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.weihua.blockchains</groupId> <artifactId>blackchain</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>blackchain</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> <version>2.1</version> </dependency> </dependencies>
</project>
Run to see the output:
Trying to Mine block 1...
Block Mined!!! : 000005b9947556fa4b14d24349728a58418c1517f8073d10a37ba3daf0ceee9c
Trying to Mine block 2...
Block Mined!!! : 00000015d3f53bd8545a3a9586aaef26abe26d78fce2da6584aac025c60c21e3
Trying to Mine block 3...
Block Mined!!! : 000000d224711a1e308e98c317cc7c900c7f4196d585266262b54e42288da65b
Blockchain is Valid: true
The block chain:
[
{
"hash": "000005b9947556fa4b14d24349728a58418c1517f8073d10a37ba3daf0ceee9c",
"previousHash": "0",
"data": "Hi im the first block",
"timeStamp": 1557928459188,
"nonce": 347042
},
{
"hash": "00000015d3f53bd8545a3a9586aaef26abe26d78fce2da6584aac025c60c21e3",
"previousHash": "000005b9947556fa4b14d24349728a58418c1517f8073d10a37ba3daf0ceee9c",
"data": "Yo im the second block",
"timeStamp": 1557928460017,
"nonce": 1394831
},
{
"hash": "000000d224711a1e308e98c317cc7c900c7f4196d585266262b54e42288da65b",
"previousHash": "00000015d3f53bd8545a3a9586aaef26abe26d78fce2da6584aac025c60c21e3",
"data": "Hey im the third block",
"timeStamp": 1557928462949,
"nonce": 81919
}
]