区块链开发之ETH钱包APP

基础知识

介绍

以太坊（英文Ethereum）是一个开源的有智能合约功能的公共区块链平台，通过其专用加密货币以太币（Ether，简称“ETH”）提供去中心化的以太虚拟机（Ethereum Virtual Machine）来处理点对点合约。

合约

合约是一个活在以太坊系统里的自动代理人，他有一个自己的以太币地址，当用户向合约的地址里发送一笔交易后，该合约就被激活，然后根据交易中的额外信息，合约会运行自身的代码，最后返回一个结果，这个结果可能是从合约的地址发出另外一笔交易。需要指出的是，以太坊中的交易，不单只是发送以太币而已，它还可以嵌入相当多的额外信息。如果一笔交易是发送给合约的，那么这些信息就非常重要，因为合约将根据这些信息来完成自身的业务逻辑。

开发准备

Web3J介绍：

web3j是一个高度模块化，反应性，类型安全的Java和Android库，用于与智能合约配合并与以太坊网络上的客户端（节点）集成：

image

功能

通过HTTP和IPC 完整实现以太坊的JSON-RPC客户端API
以太坊钱包支持
自动生成Java智能合约包装器，以从本地Java代码创建，部署，处理和调用智能合约（支持Solidity和Truffle定义格式）
响应式API，用于过滤器
以太坊名称服务（ENS）支持
支持Parity的Personal和Geth的Personal客户端API
支持Infura，因此您不必自己运行以太坊客户端
支持ERC20和ERC721令牌标准
全面的集成测试，证明了上述多种情况
命令行工具
兼容Android
通过web3j-quorum支持JP Morgan的Quorum

依赖

Java 8:

compile ('org.web3j:core:4.5.12')

Android:

implementation ('org.web3j:core:4.2.0-android')

web3j基本使用

1、同步

Web3j web3 = Web3j.build(new HttpService("节点地址"));// defaults to http://localhost:8545/
Web3ClientVersion web3ClientVersion = web3.web3ClientVersion().send();
String version = web3ClientVersion.getWeb3ClientVersion();
System.out.println("version:" + version);

2、异步

Web3j web3 = Web3j.build(new HttpService("节点地址"));  // defaults to http://localhost:8545/
web3.web3ClientVersion().sendAsync().thenAccept(new Consumer() {
    @Override
    public void accept(Web3ClientVersion web3ClientVersion) {
        System.out.println(web3ClientVersion.getWeb3ClientVersion());
    }
}).exceptionally(new Function() {
    @Override
    public Void apply(Throwable throwable) {
        throwable.printStackTrace();
        return null;
    }
});

实战开发

生成账号
1、随机生成账号

String mnemonic = ChainUtil.genMnemonic();
ECKey ecKey = ChainUtil.genECKey(mnemonic, "m/44'/60'/0'/0/0", "");
ECKeyPair keyPair = ECKeyPair.create(ecKey.getPrivKeyBytes());
File file = new File("Keystore存放的路径");
String walletFile = WalletUtils.generateWalletFile("你的密码", keyPair, file, false);
String keystore = FilesUtils.readFileString(new File(file, walletFile).getAbsolutePath());
Credentials credentials = WalletUtils.loadCredentials("你的密码", new File(file, walletFile));
String address = credentials.getAddress();
System.out.println("mnemonic:" + mnemonic);
System.out.println("privateKey:" + keyPair.getPrivateKey().toString(16));
System.out.println("publicKey:" + keyPair.getPublicKey().toString(16));
System.out.println("keystore:" + keystore);
System.out.println("address:" + address);

2、私钥导入

String privateKey = "你的私钥";
Credentials credentials = Credentials.create(privateKey);
String address = credentials.getAddress();
ECKeyPair keyPair = credentials.getEcKeyPair();
File file = new File("Keystore存放的路径");
String walletFile = WalletUtils.generateWalletFile("你的密码",keyPair,file,false);
String keystore = FilesUtils.readFileString(new File(file, walletFile).getAbsolutePath());
System.out.println("privateKey:" + keyPair.getPrivateKey().toString(16));
System.out.println("publicKey:" + keyPair.getPublicKey().toString(16));
System.out.println("keystore:" + keystore);
System.out.println("address:" + address);
//私钥是无法推算出助记词的

3、KeyStore导入

String keystore = "你的keyStore";
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
WalletFile walletFile = objectMapper.readValue(keystore, WalletFile.class);
ECKeyPair keyPair = EthWallet.decrypt("你的密码", walletFile);
String privateKey = keyPair.getPrivateKey().toString(16);
String publicKey = keyPair.getPublicKey().toString(16);
Credentials credentials = Credentials.create(privateKey, publicKey);
String address = credentials.getAddress();

System.out.println("privateKey:" + privateKey);
System.out.println("publicKey:" + publicKey);
System.out.println("keystore:" + keystore);
System.out.println("address:" + address);

4、助记词导入

String mnemonic = "你的助记词，逗号分隔";
ECKey ecKey = ChainUtil.genECKey(mnemonic, "m/44'/60'/0'/0/0", "");
ECKeyPair keyPair = ECKeyPair.create(ecKey.getPrivKeyBytes());
File file = new File("Keystore存放的路径");
String walletFile = WalletUtils.generateWalletFile("你的密码", keyPair, file, false);
String keystore = FilesUtils.readFileString(new File(file, walletFile).getAbsolutePath());
Credentials credentials = WalletUtils.loadCredentials("你的密码", new File(file, walletFile));
String address = credentials.getAddress();
System.out.println("mnemonic:" + mnemonic);
System.out.println("privateKey:" + keyPair.getPrivateKey().toString(16));
System.out.println("publicKey:" + keyPair.getPublicKey().toString(16));
System.out.println("keystore:" + keystore);
System.out.println("address:" + address);

转账

String from = "转出地址";
String to = "转入地址";
String privateKey = "你的私钥";
BigInteger value = "转出多少";
BigInteger gasPrice = "gas价格";
BigInteger gasLimit = BigInteger.valueOf(21000); //单笔转账一般取21000
Web3j web3 = Web3j.build(new HttpService("节点地址"));  // defaults to http://localhost:8545/
BigInteger nonce = web3.ethGetTransactionCount(from, DefaultBlockParameterName.LATEST).send().getTransactionCount();
RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, gasPrice, gasLimit, to, value, "");
ECKeyPair ecKeyPair = ECKeyPair.create(new BigInteger(privateKey, 16));
Credentials credentials = Credentials.create(ecKeyPair);
byte[] signMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
String signData = Numeric.toHexString(signMessage);
EthSendTransaction ethSendTransaction = web3.ethSendRawTransaction(signData).send();
String transactionHash = ethSendTransaction.getTransactionHash();
System.out.println("hash:" + transactionHash);
//获取到hash就可以查询交易状态了。

代币转账

String from = "转出地址";
String to = "转入地址";
String privateKey = "你的私钥";
BigInteger value = "转出多少";
String contract = "";//合约地址
BigInteger gasPrice = "gas价格";
BigInteger gasLimit = BigInteger.valueOf(60000); //代币转账一般取60000
Web3j web3 = Web3j.build(new HttpService("节点地址"));  // defaults to http://localhost:8545/
BigInteger nonce = web3.ethGetTransactionCount(from, DefaultBlockParameterName.LATEST).send().getTransactionCount();
Function function = new Function("transfer", Arrays.asList(new Address(to), new Uint256(value)),
Collections.singletonList(new TypeReference() {}));
String encodedFunction = FunctionEncoder.encode(function);
RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, gasPrice, gasLimit, contract, encodedFunction);
ECKeyPair ecKeyPair = ECKeyPair.create(new BigInteger(privateKey, 16));
Credentials credentials = Credentials.create(ecKeyPair);
byte[] signMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
String signData = Numeric.toHexString(signMessage);
EthSendTransaction ethSendTransaction = web3.ethSendRawTransaction(signData).send();
String transactionHash = ethSendTransaction.getTransactionHash();
System.out.println("hash:" + transactionHash);
//获取到hash就可以查询交易状态了。

获取余额

Web3j web3 = Web3j.build(new HttpService("节点地址"));  // defaults to http://localhost:8545/
String address = "获取余额的地址";
BigInteger balance = web3.ethGetBalance(address, DefaultBlockParameterName.LATEST).send().getBalance();
System.out.println("balance:" + balance);

获取代币余额

参数：
from: 钱包地址
to: 代币地址（智能合约地址）
data：0x70a08231000000000000000000000000b60e8dd61c5d32be8058bb8eb970870f07233155
//注意 data数据格式：最前边的“0x70a08231000000000000000000000000”是固定的，后边的是钱包地址（不带“0x”前缀）
QUANTITY|TAG，”latest”, “earliest” or “pending”
代码示例

Web3j web3 = Web3j.build(new HttpService("节点地址"));  // defaults to http://localhost:8545/
String address = "获取余额的地址";
String contract = "合约地址";
String tmpAddress = address;
if (tmpAddress.startsWith("0x")) {
    tmpAddress = address.substring(2); //去掉0x
}
String data = "0x70a08231000000000000000000000000"+tmpAddress;
Transaction transaction = Transaction.createEthCallTransaction(address, contract, data);
String balance = web3.ethCall(transaction, DefaultBlockParameterName.LATEST).send().getValue();
System.out.println("balance:" + balance);

总结

1、导入钱包踩坑
导入轻钱包解析失败解决方案Out Of Memory exception when using web3j in Android
解决办法

implementation ‘com.lambdaworks:scrypt:1.4.0’//解决oom错误的依赖

因为在导入keystore解析时，只是这句报错常规的：ECKeyPair keyPair = ECKeyPair.create(privateKeyByte);报错，
这个错误，是因为重钱包不能被解析轻钱包的方法解析，keyStore中crypto.kdfparams.n: 262144,这个数值很大，一般常规的轻钱包n值是：4000左右，或者是个四位数。
对于解决办法，查了很多资料，最后找到了。替换下面代码即可。

//derivedKey = generateDerivedScryptKey(password.getBytes(Charset.forName("UTF-8")), salt, n, r, p, dklen);
derivedKey = com.lambdaworks.crypto.SCrypt.scrypt(password.getBytes(StandardCharsets.UTF_8), salt, n, r, p, dklen);

2、实现以太坊钱包相对还是容易一些，毕竟提供了相关的SDK，实现起来也容易，主要是掌握web3j的API使用，如果选择其他的以太坊SDK也是差不多的，只是熟悉API的调用即可。

参考文献

ethereum github: https://github.com/ethereum
web3j github: https://github.com/web3j/web3j/
web3j 官网: https://docs.web3j.io/
感谢代币余额查询文章：https://blog.csdn.net/wypeng2010/article/details/81362562
感谢转账和代币转账文章：https://www.jianshu.com/p/8ae984e6bafc
感谢解决Android OOM 文章https://blog.csdn.net/jian11058/article/details/100133979