SpringBoot区块链之以太坊开发（整合Web3j）

最近公司需要ETH兑换功能，ETH转账需要区块打包，这个时候就需要区块检测，目前只是简单整合，后面会将区块自动检测代码上传致QQ群
对于区块链开发不太熟悉的童鞋，可以看看：[区块链开发（零）如何开始学习以太坊及区块链](https://blog.csdn.net/sportshark/article/details/52351415)
欢迎大家加企鹅群一起讨论：260532022
首先引入一下依赖pom.xml，主要依赖是 org.web3j
```

4.0.0

org.springframework.boot
spring-boot-starter-parent
2.1.8.RELEASE

com.xiaobin
eth-demo
0.0.1-SNAPSHOT
eth-demo
Demo project for Spring Boot

1.8

org.springframework.boot
spring-boot-starter-web

org.springframework.boot
spring-boot-devtools
runtime
true

org.projectlombok
lombok
true

org.web3j
core
3.4.0

com.github.briandilley.jsonrpc4j
jsonrpc4j
1.4.6

com.mashape.unirest
unirest-java
1.4.9

org.springframework.boot
spring-boot-starter-test
test

org.springframework.boot
spring-boot-maven-plugin

```
接下来在application.yml文件中配置以太坊节点路径，这个节点可以使用测试节点
```
spring:
application:
name: xiaobin-eth-demo
server:
port: 8080
web3j:
client-address: http://localhost:8545
```
再就是需要将Web3j对象交给Spring进行管理
```
package com.xiaobin.ethdemo.config;

import com.googlecode.jsonrpc4j.JsonRpcHttpClient;
import okhttp3.OkHttpClient;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.http.HttpService;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
/**
* 创建时间： 2019/9/23 23:21
* 备注：
* 码农自学交流小群：260532022，欢迎大家的加入，分享学习是一件开心事
**/
@Configuration
public class EthConfig {

@Value("${web3j.client-address}")
private String rpc;

@Bean
public Web3j web3j() {
OkHttpClient.Builder builder = new OkHttpClient.Builder();
builder.connectTimeout(30*1000, TimeUnit.MILLISECONDS);
builder.writeTimeout(30*1000, TimeUnit.MILLISECONDS);
builder.readTimeout(30*1000, TimeUnit.MILLISECONDS);
OkHttpClient httpClient = builder.build();
Web3j web3j = Web3j.build(new HttpService(rpc,httpClient,false));
return web3j;
}
}
```
Controller测试一下
```
package com.xiaobin.ethdemo.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.methods.response.EthBlockNumber;

/**
* 创建时间： 2019/9/23 23:32
* 备注：
* 码农自学交流小群：260532022，欢迎大家的加入，分享学习是一件开心事
**/
@RestController
@RequestMapping("/eth")
public class WalletController {
@Autowired
private Web3j web3j;

@GetMapping("height")
public long getHeight() {
try {
EthBlockNumber blockNumber = web3j.ethBlockNumber().send();
long blockHeight = blockNumber.getBlockNumber().longValue();
return blockHeight;
} catch (Exception e) {
e.printStackTrace();
}
return 0;
}
}
```
获取当前以太坊节点高度，访问结果图

当然还有更多的方法，这里没有去测试了，大家有空可以自己测测哦

#### 获取账户的Nonce
```
public static BigInteger getNonce(Web3j web3j, String addr) {
try {
EthGetTransactionCount getNonce = web3j.ethGetTransactionCount(addr, DefaultBlockParameterName.PENDING).send();

if (getNonce == null){
throw new RuntimeException("net error");
}
return getNonce.getTransactionCount();
} catch (IOException e) {
throw new RuntimeException("net error");
}
}
```
#### 获取ETH余额
```
public static BigInteger getNonce(Web3j web3j, String addr) {
try {
EthGetTransactionCount getNonce = web3j.ethGetTransactionCount(addr, DefaultBlockParameterName.PENDING).send();

if (getNonce == null){
throw new RuntimeException("net error");
}
return getNonce.getTransactionCount();
} catch (IOException e) {
throw new RuntimeException("net error");
}
}
```

#### 获取代币余额
```
public static BigInteger getTokenBalance(Web3j web3j, String fromAddress, String contractAddress) {

String methodName = "balanceOf";
List inputParameters = new ArrayList();
List> outputParameters = new ArrayList();
Address address = new Address(fromAddress);
inputParameters.add(address);

TypeReference typeReference = new TypeReference() {
};
outputParameters.add(typeReference);
Function function = new Function(methodName, inputParameters, outputParameters);
String data = FunctionEncoder.encode(function);
Transaction transaction = Transaction.createEthCallTransaction(fromAddress, contractAddress, data);

EthCall ethCall;
BigInteger balanceValue = BigInteger.ZERO;
try {
ethCall = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).send();
List results = FunctionReturnDecoder.decode(ethCall.getValue(), function.getOutputParameters());
balanceValue = (BigInteger) results.get(0).getValue();
} catch (IOException e) {
e.printStackTrace();
}
return balanceValue;
}
```
#### 转账ETH
```
public static String transferETH(Web3j web3j, String fromAddr, String privateKey, String toAddr, BigDecimal amount, String data){
// 获得nonce
BigInteger nonce = getNonce(web3j, fromAddr);
// value 转换
BigInteger value = Convert.toWei(amount, Convert.Unit.ETHER).toBigInteger();

// 构建交易
Transaction transaction = Transaction.createEtherTransaction(fromAddr, nonce, gasPrice, null, toAddr, value);
// 计算gasLimit
BigInteger gasLimit = getTransactionGasLimit(web3j, transaction);

// 查询调用者余额，检测余额是否充足
BigDecimal ethBalance = getBalance(web3j, fromAddr);
BigDecimal balance = Convert.toWei(ethBalance, Convert.Unit.ETHER);
// balance ChainId.NONE){
signMessage = TransactionEncoder.signMessage(rawTransaction, chainId, credentials);
} else {
signMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
}

String signData = Numeric.toHexString(signMessage);
if (!"".equals(signData)) {
try {
EthSendTransaction send = web3j.ethSendRawTransaction(signData).send();
txHash = send.getTransactionHash();
System.out.println(JSON.toJSONString(send));
} catch (IOException e) {
throw new RuntimeException("交易异常");
}
}
return txHash;
}
```
有什么问题或者缺少什么依赖包，可以加QQ群哦

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