区块链这么火的技术，大java怎能落后，所以有了本文，主要代码参考自 Learn Blockchains by Building One , 中文翻译：用Python从零开始创建区块链 。
一、区块链对象模型的基础属性(BlockChain)
区块链的基本数据模型参考：最基本的区块链hello world(python3实现) 。主要属性如下：
@ApiModelProperty(value = "当前交易列表", dataType = "List<Transaction>")
@JSONField(serialize = false)
@JsonIgnore
private List<Transaction> currentTransactions; @ApiModelProperty(value = "所有交易列表", dataType = "List<Transaction>")
private List<Transaction> transactions; @ApiModelProperty(value = "区块列表", dataType = "List<BlockChain>")
@JSONField(serialize = false)
@JsonIgnore
private List<BlockChain> chain; @ApiModelProperty(value = "集群的节点列表", dataType = "Set<String>")
@JSONField(serialize = false)
@JsonIgnore
private Set<String> nodes; @ApiModelProperty(value = "上一个区块的哈希值", dataType = "String", example = "f461ac428043f328309da7cac33803206cea9912f0d4e8d8cf2786d21e5ff403")
private String previousHash = ""; @ApiModelProperty(value = "工作量证明", dataType = "Integer", example = "100")
private Integer proof = 0; @ApiModelProperty(value = "当前区块的索引序号", dataType = "Long", example = "2")
private Long index = 0L; @ApiModelProperty(value = "当前区块的时间戳", dataType = "Long", example = "1526458171000")
private Long timestamp = 0L; @ApiModelProperty(value = "当前区块的哈希值", dataType = "String", example = "g451ac428043f328309da7cac33803206cea9912f0d4e8d8cf2786d21e5ff401")
private String hash;
注：上面有些注解来自swagger，主要为了方便生成在线文档以及直接调试rest接口。相对之前最基本的区块链hello world(python3实现)一文，每个区块中的data，在这里细分为transactions、currentTransactions。另外区块“链”本质上可以理解为链表，所以得有一个List<?> chain；此外这里引入了所谓“工作量证明”，用于验证每个区域的hash值不是随便来的，而是要达到一定规则的运算量才能获取，可以理解为控制挖矿速度的难度系数。
二、BlockChain的常规操作
2.1 生成新块newBlock
public BlockChain newBlock(Integer proof, String previousHash) {
BlockChain block = new BlockChain();
block.index = chain.size() + 1L;
block.timestamp = System.currentTimeMillis();
block.transactions.addAll(currentTransactions);
block.proof = proof;
block.previousHash = previousHash;
currentTransactions.clear();
chain.add(block);
return block;
}
2.2 生成第1个"创世"块
链表总归要有一个Head节点，区块链也不例外
public void newSeedBlock() {
newBlock(100, "1");
}
约定previousHash=1的，即为所谓的"创世"块
2.3 生成hash值
public String getHash() {
String json = jsonUtil.toJson(this.getCurrentTransactions()) +
jsonUtil.toJson(this.getTransactions()) +
jsonUtil.toJson(this.getChain()) +
this.getPreviousHash() + this.getProof() + this.getIndex() + this.getTimestamp();
hash = SHAUtils.getSHA256Str(json);
return hash;
}
这里把区块的主要属性：交易数据、链表中所有元素、工作量证明、区块索引号、时间戳 拼在一起，然后计算sha256。总之，这些主要属性中的任何一个属性发生变化，整个hash值就变了。
2.4 工作量证明
相信对区块链有了解的同学，都知道“挖矿”。为了控制挖矿的难度，得有一个规则来约束下，所以就有了这个工作量证明，这里我们模拟一个简单的策略：
public Boolean validProof(Integer lastProof, Integer proof) {
System.out.println("validProof==>lastProof:" + lastProof + ",proof:" + proof);
String guessHash = SHAUtils.getSHA256Str(String.format("{%d}{%d}", lastProof, proof));
return guessHash.startsWith("00");
}
把上一块的proof值与本区块的proof在一起，算sha256值，如果正好前2位是00，表示证明通过。（注：0的个数越多，挖矿难度越大，有兴趣的同学可以自己调整试下)
2.5 区块链验证数据是否正确
为了防止区块链的节点中混入非法脏数据（或被篡改），需要一个检测数据完整性的方法
public boolean validChain(List<BlockChain> chain) {
if (CollectionUtils.isEmpty(chain)) {
return false;
}
BlockChain previousBlock = chain.get(0);
int currentIndex = 1;
while (currentIndex < chain.size()) {
BlockChain block = chain.get(currentIndex);
if (!block.getPreviousHash().equals(previousBlock.getHash())) {
return false;
}
if (!validProof(previousBlock.getProof(), block.getProof())) {
return false;
}
previousBlock = block;
currentIndex += 1;
}
return true;
}
规则很简单：
a）每个区块的previousHash值，必须等于前一个块的hash值
b) 验证每个块上的proof值是否有效
2.6 集群中的分叉校验
区块链是一个去中心化的分布式体系，每个节点都能挖矿，挖出来的“新区块”都能加入链中，如果出现节点之间的区块链数据不一致，需要一个策略来做仲裁，可以定一个简单的规则：链最长的节点认定为有效的，其它节点都以此为准。
为了模拟这种情况，在BlockChain类的属性中，特地留了一个nodes节点列表，用于登记集群中的其它节点信息。
public void registerNode(String address) {
nodes.add(address);
}
上面的方法，将把其它节点的实例（类似http://localhost:8081/)，登记到节点列表中。知道了集群中所有其它节点，就可以一一检查谁的链条最长，代码如下：
public boolean resolveConflicts() {
int maxLength = getChain().size();
List<BlockChain> newChain = new ArrayList<>();
for (String node : getNodes()) {
RestTemplate template = new RestTemplate();
Map map = template.getForObject(node + "chain", Map.class);
int length = MapUtils.getInteger(map, "length");
String json = jsonUtil.toJson(MapUtils.getObject(map, "chain"));
List<BlockChain> chain = jsonUtil.fromJson(json, new TypeReference<List<BlockChain>>() {
});
if (length > maxLength && validChain(chain)) {
maxLength = length;
newChain = chain;
}
}
if (!CollectionUtils.isEmpty(newChain)) {
this.chain = newChain;
return true;
}
return false;
}
大意是遍历整个节点，逐一请求其它节点的rest接口，获取其完整的链表，然后跟自己对比，如果比自己长的，就把自己给换掉。这样轮一圈后，自身的链表，就被替换为整个集群中最长的那个。
三、调试运行
为了方便调试，本文引入了swagger(不熟悉的同学可以参考spring cloud 学习(10) - 利用springfox集成swagger一文)，然后加一堆rest api，跑起来，就可以直接测了：
3.1 调用/chain查看下初始值：
{
"chain": [
{
"transactions": [],
"previousHash": "1",
"proof": 100,
"index": 1,
"timestamp": 1527427873298,
"hash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479"
}
],
"length": 1
}
可以看到就只有一个“创世”块，其previousHash为特定值1
3.2 调用/mine挖一块矿
{
"previousHash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479",
"index": 2,
"proof": 172,
"message": "New Block Forged",
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
]
}
挖到矿（即：产生一个新的区块block)，系统自动奖励本节点1个币（从transaction可以看出这一点），同时这笔奖励的交易被写入新块中。这时再来看下/chain
{
"chain": [
{
"transactions": [],
"previousHash": "1",
"proof": 100,
"index": 1,
"timestamp": 1527427873298,
"hash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479",
"proof": 172,
"index": 2,
"timestamp": 1527427956435,
"hash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93"
}
],
"length": 2
}
可以看到，有二个区块加入"链表"中了，可以继续再挖一块，最终/chain可能长成这样：
{
"chain": [
{
"transactions": [],
"previousHash": "1",
"proof": 100,
"index": 1,
"timestamp": 1527427873298,
"hash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479",
"proof": 172,
"index": 2,
"timestamp": 1527427956435,
"hash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93",
"proof": 153,
"index": 3,
"timestamp": 1527428128077,
"hash": "d2b50c6ae768fd48591d07a054de78d058c11f889cec15588d270f72b6e420f1"
}
],
"length": 3
}
3.3 调用/transactions/new 发起一笔新交易
参数如下：
{
"amount": 1.0,
"recepient": "block-on-other-node",
"sender": "50130c5283e640779b4e5e7a5afd2e6b"
}
注：sender一般取为当前矿机的标识，即本节点的nodeId，接收方一般指其它节点（这里我们随便输入点内容，当作演示），然后交易的金额为“1”个币，成功后，将返回
{
"message": "Transaction will be added to Block 4"
}
但这时，如果调用/chain查看整个链的数据，会发现没有变化，因为这笔交易数据，只是放在本区块的currentTransactions列表中（注：该属性并未json序列化输出，忘记的同学，可以拉到本文最开头，复习下几个重要的属性）。只有下一个可用区块产生时，这笔交易才会写入新的区块中，so，我们再继续挖一块新矿，调用/mine，然后再查看/chain
{
"chain": [
{
"transactions": [],
"previousHash": "1",
"proof": 100,
"index": 1,
"timestamp": 1527427873298,
"hash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479",
"proof": 172,
"index": 2,
"timestamp": 1527427956435,
"hash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93",
"proof": 153,
"index": 3,
"timestamp": 1527428128077,
"hash": "d2b50c6ae768fd48591d07a054de78d058c11f889cec15588d270f72b6e420f1"
},
{
"transactions": [
{
"sender": "50130c5283e640779b4e5e7a5afd2e6b",
"recepient": "block-on-other-node",
"amount": 1
},
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "d2b50c6ae768fd48591d07a054de78d058c11f889cec15588d270f72b6e420f1",
"proof": 86,
"index": 4,
"timestamp": 1527428477991,
"hash": "4b3c261d2f878cebbdc1ade1a09809bb647abbd990353e529f630220a53d60ed"
}
],
"length": 4
}
刚才的交易，已经被写入最后一个刚挖出的Block中。
3.4 模拟多节点数据不一致，使用/resolve仲裁解决
a) 再启动一个新端口的运行实例
方法一：参考下图，idea中设置运行时的环境变量，填上server.port=8081，就可以在另一个端口上启动
方法二：在build.gradle里加一个task
task 8081 << {
bootRun.systemProperty 'server.port', '8081'
}
然后就可以命令行下，直接gradle 8081 bootRun
方法三：java -jar xxx.jar --name="Spring" --server.port=8081 直接在运行jar的时候指定端口
b) 调用/register 将新节点实例（即：8081端口的节点)，注册到8080的节点上
参数如下：
{
"nodes": [
"http://localhost:8081/"
]
}
反过来，把8080老节点也注册到新节点上（即：相当于两两相互注册)。注册成功后，这时调用8081新节点上的/chain ，因为这是个新节点，里面只有一个创世块，显然跟8080老节点上的数据不一致
c) 新8081节点上调用/resolve
输出如下：
{
"newChain": [
{
"transactions": [],
"previousHash": "1",
"proof": 100,
"index": 1,
"timestamp": 1527427873298,
"hash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "9fbb08a5f332baf42012b8541122eccb60a603834fa98e9b5789898022b23479",
"proof": 172,
"index": 2,
"timestamp": 1527427956435,
"hash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93"
},
{
"transactions": [
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "df079acca767eaca611383f7b1bb2b37daa3b01502f3219cb79ecddd010f7d93",
"proof": 153,
"index": 3,
"timestamp": 1527428128077,
"hash": "d2b50c6ae768fd48591d07a054de78d058c11f889cec15588d270f72b6e420f1"
},
{
"transactions": [
{
"sender": "50130c5283e640779b4e5e7a5afd2e6b",
"recepient": "block-on-other-node",
"amount": 1
},
{
"sender": "0",
"recepient": "50130c5283e640779b4e5e7a5afd2e6b",
"amount": 1
}
],
"previousHash": "d2b50c6ae768fd48591d07a054de78d058c11f889cec15588d270f72b6e420f1",
"proof": 86,
"index": 4,
"timestamp": 1527428477991,
"hash": "4b3c261d2f878cebbdc1ade1a09809bb647abbd990353e529f630220a53d60ed"
}
],
"message": "Our chain was replaced"
}
最后一行的message: Our chain was replaced 表示，本节点的区块链已经被集群其它节点中最长的那个替换掉了。
最后，文中演示的所有代码，已经托管在github上，地址：https://github.com/yjmyzz/springboot-blockchain-helloworld 欢迎大家Fork.