一、Web3j入門

以太坊推出了web3.js的nodejs庫，但是對於學Java出身的而言非常的不習慣，在github中尋找到了Java版本的web3j。輕量級客戶端與以太坊互動的Java庫。
web3j github地址：https://github.com/web3j/web3j
web3j 文件地址：https://web3j.readthedocs.io/en/latest/

一個簡單的例子：
1、建立一個maven專案
2、增加dependencies

<dependency>
   <groupId>org.web3j</groupId>
   <artifactId
 
>core</artifactId>
   <version>3.3.1</version>
</dependency>

import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.methods.response.Web3ClientVersion;
import org.web3j.protocol.http.HttpService;

public class Web3Blog1_1 {
    public static void main(String[] args) throws Exception{
        Web3j web3 = Web3j.build
 
(new HttpService("https://ropsten.infura.io/rq6f6P9wex66SUNzvnDz"));
        Web3ClientVersion web3ClientVersion = web3.web3ClientVersion().send();
        String clientVersion = web3ClientVersion.getWeb3ClientVersion();
        System.out.println(clientVersion);
    }
}

注：
1.程式碼地址為：https://mainnet.infura.io/rq6f6P9wex66SUNzvnDz

輸出結果為：Geth/v1.8.13-patched-infura-omnibus-b59d4428/linux-amd64/go1.9.2
2.程式碼地址為：https://infuranet.infura.io/rq6f6P9wex66SUNzvnDz
輸出結果為：Parity//v1.6.6-beta-8c6e3f3-20170411/x86_64-linux-gnu/rustc1.16.0
3.程式碼地址為：https://kovan.infura.io/rq6f6P9wex66SUNzvnDz
輸出結果為：Parity//v1.10.6-stable-bc0d134-20180605/x86_64-linux-gnu/rustc1.26.1
4.程式碼地址為：https://rinkeby.infura.io/rq6f6P9wex66SUNzvnDz
輸出結果為：Geth/v1.8.13-stable/linux-amd64/go1.9.2

二、Transaction轉賬

為了完成以太坊交易，必須有幾個先決條件
1、對方的以太坊地址
2、確定要轉賬的金額
3、自己地址的轉賬許可權
4、大於轉賬金額的以太幣，以太幣轉賬其實就是提出一個交易，礦工會幫你計算，計算完成即達成交易，但是礦工計算需要支付一定的費用（GAS），支付過少，計算轉賬就有可能很慢或者不成功。
 
轉賬方式1：

import org.web3j.crypto.Credentials;
import org.web3j.crypto.RawTransaction;
import org.web3j.crypto.TransactionEncoder;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.DefaultBlockParameterName;
import org.web3j.protocol.core.methods.response.EthGetTransactionCount;
import org.web3j.protocol.core.methods.response.EthSendTransaction;
import org.web3j.protocol.http.HttpService;
import org.web3j.utils.Convert;
import org.web3j.utils.Numeric;

import java.math.BigInteger;


public class TransactionTest {
    public static void main(String[] args) throws Exception {
        //設定需要的礦工費
        BigInteger GAS_PRICE = BigInteger.valueOf(22_000_000_000L);
        BigInteger GAS_LIMIT = BigInteger.valueOf(4_300_000);

        //呼叫的是kovan測試環境，這裡使用的是infura這個客戶端
        Web3j web3j = Web3j.build(new HttpService("https://kovan.infura.io/<your-token>"));
        //轉賬人賬戶地址
        String ownAddress = "0xD1c82c71cC567d63Fd53D5B91dcAC6156E5B96B3";
        //被轉人賬戶地址
        String toAddress = "0x6e27727bbb9f0140024a62822f013385f4194999";
        //轉賬人私鑰
        Credentials credentials = Credentials.create("xxxxxxxxxxxxx");
        //        Credentials credentials = WalletUtils.loadCredentials(
        //                "123",
        //                "src/main/resources/UTC--2018-03-01T05-53-37.043Z--d1c82c71cc567d63fd53d5b91dcac6156e5b96b3");

        EthGetTransactionCount ethGetTransactionCount = web3j.ethGetTransactionCount(
                ownAddress, DefaultBlockParameterName.LATEST).sendAsync().get();
        BigInteger nonce = ethGetTransactionCount.getTransactionCount();

        //建立交易，這裡是轉0.5個以太幣
        BigInteger value = Convert.toWei("0.5", Convert.Unit.ETHER).toBigInteger();
        RawTransaction rawTransaction = RawTransaction.createEtherTransaction(
                nonce, GAS_PRICE, GAS_LIMIT, toAddress, value);

        //簽名Transaction，這裡要對交易做簽名
        byte[] signedMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
        String hexValue = Numeric.toHexString(signedMessage);

        //傳送交易
        EthSendTransaction ethSendTransaction =
                web3j.ethSendRawTransaction(hexValue).sendAsync().get();
        String transactionHash = ethSendTransaction.getTransactionHash();

        //獲得到transactionHash後就可以到以太坊的網站上查詢這筆交易的狀態了
        System.out.println(transactionHash);
    }
}

1、第27-31行，可以用兩種方式獲得地址的信任憑證，一種是直接使用私鑰，一種是使用keystore檔案
2、https://kovan.etherscan.io/tx/0x0d29fa7db4503f94fd6f4c7894a1fb21a628d96f48f408efc19554d812628a81
這個地址是可以查到你的這筆交易的
0x0d29fa7db4503f94fd6f4c7894a1fb21a628d96f48f408efc19554d812628a81是transactionHash
這個地址是測試地址，如果需要查詢主網上的，刪除kovan
 
轉賬方式2：

import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.methods.response.TransactionReceipt;
import org.web3j.protocol.http.HttpService;
import org.web3j.tx.Transfer;
import org.web3j.utils.Convert;

import java.math.BigDecimal;

public class TransactionTest2 {
    public static void main(String[] args) throws Exception {
        Web3j web3j = Web3j.build(new HttpService("https://kovan.infura.io/<your-token>"));
        // 被轉人賬戶地址
        String toAddress = "0x6e27727bbb9f0140024a62822f013385f4194999";
        // 轉賬人私鑰
        Credentials credentials = Credentials.create("xxxxxxxx");

        TransactionReceipt transactionReceipt = Transfer.sendFunds(
                web3j, credentials, toAddress,
                BigDecimal.valueOf(0.2), Convert.Unit.ETHER).send();

        System.out.println(transactionReceipt.getTransactionHash());
    }
}

注意：
這兩種方式都是離線的，但是第二種程式碼量比較小。

備註：
如果在kovan環境中沒有以太幣的話，可以到https://gitter.im/kovan-testnet/faucet這裡去要，直接註冊賬號之後，把你的賬號地址發到群裡就行了，過幾分鐘就會給你轉錢的（每次只給你轉3個eth且中間間隔為6天），主網的賬號地址和kovan是一樣的，但是裡面的幣是不一樣的。



 

三、智慧合約

1、首先我們需要一份寫好的智慧合約

pragma solidity ^0.4.18;

// Example taken from https://www.ethereum.org/greeter, also used in
// https://github.com/ethereum/go-ethereum/wiki/Contract-Tutorial#your-first-citizen-the-greeter

contract mortal {
    /* Define variable owner of the type address*/
    address owner;

    /* this function is executed at initialization and sets the owner of the contract */
    function mortal() { owner = msg.sender; }

    /* Function to recover the funds on the contract */
    function kill() { if (msg.sender == owner) suicide(owner); }
}

contract greeter is mortal {
    /* define variable greeting of the type string */
    string greeting;

    /* this runs when the contract is executed */
    function greeter(string _greeting) public {
        greeting = _greeting;
    }

    /* main function */
    function greet() constant returns (string) {
        return greeting;
    }
}

2、進入https://remix.ethereum.org/ 網站，此網站是線上智慧合約編譯網站，所以比較簡便，不需要安裝truffle等工具

點選圖示中details按鈕，會出現智慧合約的ABI和BIN
注：對已經部署好的智慧合約也可以直接在https://etherscan.io/查詢獲得

將BYTECODE中的object複製下來儲存成greeter.bin，點選ABI（Application Binary Interface：應用程式二進位制介面，定義了智慧合約提供的方法功能）旁邊的複製按鈕將其儲存成greeter.abi

進入https://github.com/web3j/web3j/releases/tag/v3.3.1網站，下載web3j-3.3.1.tar，並解壓。

進入目錄bin下，將greeter.bin和greeter.abi，複製到目錄下，在此目錄命令列執行

web3j solidity generate --javaTypes greeter.bin greeter.abi -o src/ -p com.your.organisation.name

web3j solidity generate [–javaTypes|–solidityTypes] /path/to/.bin /path/to/.abi -o /path/to/src/main/java -p com.your.organisation.name
-o 是原始碼要放的目錄，-p是包名，–javaTypes也可以選擇–solidityTypes
生成出來Greeter.java

import org.web3j.abi.FunctionEncoder;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.Function;
import org.web3j.abi.datatypes.Type;
import org.web3j.abi.datatypes.Utf8String;
import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.RemoteCall;
import org.web3j.protocol.core.methods.response.TransactionReceipt;
import org.web3j.tx.Contract;
import org.web3j.tx.TransactionManager;

import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collections;

public class Greeter extends Contract {
    private static final String BINARY = "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";

    protected Greeter(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
        super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

    protected Greeter(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
        super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }

    public RemoteCall<TransactionReceipt> kill() {
        Function function = new Function(
                "kill",
                Arrays.<Type>asList(),
                Collections.<TypeReference<?>>emptyList());
        return executeRemoteCallTransaction(function);
    }

    public RemoteCall<String> greet() {
        Function function = new Function("greet",
                Arrays.<Type>asList(),
                Arrays.<TypeReference<?>>asList(new TypeReference<Utf8String>() {}));
        return executeRemoteCallSingleValueReturn(function, String.class);
    }

    public static RemoteCall<Greeter> deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit, String _greeting) {
        String encodedConstructor = FunctionEncoder.encodeConstructor(Arrays.<Type>asList(new org.web3j.abi.datatypes.Utf8String(_greeting)));
        return deployRemoteCall(Greeter.class, web3j, credentials, gasPrice, gasLimit, BINARY, encodedConstructor);
    }

    public static RemoteCall<Greeter> deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit, String _greeting) {
        String encodedConstructor = FunctionEncoder.encodeConstructor(Arrays.<Type>asList(new org.web3j.abi.datatypes.Utf8String(_greeting)));
        return deployRemoteCall(Greeter.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, encodedConstructor);
    }

    public static Greeter load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
        return new Greeter(contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

    public static Greeter load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
        return new Greeter(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }
}

3、部署智慧合約

import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.http.HttpService;
import org.web3j.tx.Contract;

public class SmartContractTest {
    public static void main(String[] args) throws Exception {
        Web3j web3j = Web3j.build(new HttpService("https://kovan.infura.io/<your-token>"));
        Credentials credentials = Credentials.create("xxxxxxxxxxxxxxxxxxx");
        //部署智慧合約
        Greeter greeter = Greeter.deploy(web3j,credentials,Contract.GAS_PRICE,Contract.GAS_LIMIT,"zx").send();
        System.out.println(greeter.getContractAddress());
        //呼叫智慧合約
        System.out.println(greeter.greet().send());
    }
}