Web3jを使った軽量のEthereumクライアント

$ truffle init
$ truffle compile
$ truffle migrate
$ truffle test

pragma solidity ^0.4.17;

contract Example {
  function Example() {
   //constructor
  }
}

{
  "contractName": "Example",
  "abi":[    {
      "inputs":[],
      "payable": false,
      "stateMutability": "nonpayable",
      "type": "constructor"
    }
 ],
  "bytecode": "0x60606040523415600e57600080fd5b603580601b6...,
  "deployedBytecode": "0x6060604052600080fd00a165627a7a72305...,
 //...
}

public CompletableFuture<EthBlockNumber> getBlockNumber() {
    EthBlockNumber result = new EthBlockNumber();
    result = this.web3j.ethBlockNumber()
      .sendAsync()
      .get();
    return CompletableFuture.completedFuture(result);
}

public CompletableFuture<EthAccounts> getEthAccounts() {
    EthAccounts result = new EthAccounts();
    result = this.web3j.ethAccounts()
        .sendAsync()
        .get();
    return CompletableFuture.completedFuture(result);
}

public CompletableFuture<EthGetTransactionCount> getTransactionCount() {
    EthGetTransactionCount result = new EthGetTransactionCount();
    result = this.web3j.ethGetTransactionCount(DEFAULT__ADDRESS,
      DefaultBlockParameter.valueOf("latest"))
        .sendAsync()
        .get();
    return CompletableFuture.completedFuture(result);
}

public CompletableFuture<EthGetBalance> getEthBalance() {
    EthGetBalance result = new EthGetBalance();
    this.web3j.ethGetBalance(DEFAULT__ADDRESS,
      DefaultBlockParameter.valueOf("latest"))
        .sendAsync()
        .get();
    return CompletableFuture.completedFuture(result);
}

$ web3j truffle generate[--javaTypes|--solidityTypes]
 /path/to/<truffle-smart-contract-output>.json
  -o/path/to/src/main/java -p com.your.organisation.name

web3j truffle generate dev__truffle/build/contracts/Example.json
  -o src/main/java/com/baeldung/web3/contract -p com.baeldung

public class Example extends Contract {
    private static final String BINARY = "0x60606040523415600e576...";
   //...
}

WalletUtils.generateNewWalletFile("PASSWORD", new File("/path/to/destination"), true);

Credentials credentials = WalletUtils.loadCredentials("PASSWORD", "/path/to/walletfile");

Example contract = Example.deploy(this.web3j,
  credentials,
  ManagedTransaction.GAS__PRICE,
  Contract.GAS__LIMIT).send();

contractAddress = contract.getContractAddress();

List inputParams = new ArrayList();
List outputParams = new ArrayList();
Function function = new Function("fuctionName", inputParams, outputParams);
String encodedFunction = FunctionEncoder.encode(function);

BigInteger nonce = BigInteger.valueOf(100);
BigInteger gasprice = BigInteger.valueOf(100);
BigInteger gaslimit = BigInteger.valueOf(100);

Transaction transaction = Transaction
  .createFunctionCallTransaction("FROM__ADDRESS",
    nonce, gasprice, gaslimit, "TO__ADDRESS", encodedFunction);

EthSendTransaction transactionResponse = web3j.ethSendTransaction(transaction).sendAsync().get();
transactionHash = transactionResponse.getTransactionHash();