在上一篇文章中講解了ETH轉(zhuǎn)賬，這一篇講一下ERC-20 Token轉(zhuǎn)賬。
【ETH錢包開發(fā)03】web3j轉(zhuǎn)賬ETH

ERC-20 Token轉(zhuǎn)賬的2種方式

1、直接用web3j的API
2、java／Android調(diào)用合約的transfer方法

不管用哪種方式來轉(zhuǎn)賬，你都需要先寫一個(gè)solidity智能合約文件來創(chuàng)建ERC-20 Token，然后部署合約，最后才是通過客戶端來調(diào)用。

web3j API轉(zhuǎn)賬ERC-20 Token

/**
     * ERC-20Token交易
     *
     * @param from
     * @param to
     * @param value
     * @param privateKey
     * @param data       附加信息需要轉(zhuǎn)換成16進(jìn)制數(shù)
     * @return
     * @throws Exception
     */
    public EthSendTransaction transferERC20Token(String from,
                                                 String to,
                                                 BigInteger value,
                                                 String privateKey,
                                                 String contractAddress) throws Exception {
        //加載轉(zhuǎn)賬所需的憑證总寻，用私鑰
        Credentials credentials = Credentials.create(privateKey);
        //獲取nonce铸董，交易筆數(shù)
        BigInteger nonce = getNonce(from);
        //get gasPrice
        BigInteger gasPrice = requestCurrentGasPrice();
        BigInteger gasLimit = Contract.GAS_LIMIT;

        //創(chuàng)建RawTransaction交易對(duì)象
        Function function = new Function(
                "transfer",
                Arrays.asList(new Address(to), new Uint256(value)),
                Arrays.asList(new TypeReference<Type>() {
                }));

        String encodedFunction = FunctionEncoder.encode(function);

        RawTransaction rawTransaction = RawTransaction.createTransaction(nonce,
                gasPrice,
                gasLimit,
                contractAddress, encodedFunction);


        //簽名Transaction，這里要對(duì)交易做簽名
        byte[] signMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
        String hexValue = Numeric.toHexString(signMessage);
        //發(fā)送交易
        EthSendTransaction ethSendTransaction = web3j.ethSendRawTransaction(hexValue).sendAsync().get();
        return ethSendTransaction;
    }

   /**
     * 獲取nonce沉衣，交易筆數(shù)
     *
     * @param from
     * @return
     * @throws ExecutionException
     * @throws InterruptedException
     */
    private BigInteger getNonce(String from) throws ExecutionException, InterruptedException {
        EthGetTransactionCount transactionCount = web3j.ethGetTransactionCount(from, DefaultBlockParameterName.LATEST).sendAsync().get();
        BigInteger nonce = transactionCount.getTransactionCount();
        Log.i(TAG, "transfer nonce : " + nonce);
        return nonce;
    }

注意：erc-20 token轉(zhuǎn)賬和eth轉(zhuǎn)賬的區(qū)別如下：
1肥隆、erc-20 token創(chuàng)建交易對(duì)象用的是這個(gè)方法createTransaction

2吸占、erc-20 token需要構(gòu)建Function初厚，它其實(shí)對(duì)應(yīng)的就是erc-20 token合約中的那些方法。它的第一個(gè)參數(shù)就是ERC20中那幾個(gè)方法的名稱，第二個(gè)參數(shù)的話就是對(duì)應(yīng)合約方法中的參數(shù)僧著，第三個(gè)參數(shù)是和第二個(gè)參數(shù)對(duì)應(yīng)的皆怕，按照我那樣就行了岂津。轉(zhuǎn)賬的話就是transfer，我們從合約的transfer可以看到第一個(gè)參數(shù)是收款地址，第二個(gè)參數(shù)是金額，所以Function這里對(duì)應(yīng)起來就好。

      //創(chuàng)建Function對(duì)象
        Function function = new Function(
                "transfer",
                Arrays.asList(new Address(to), new Uint256(value)),
                Arrays.asList(new TypeReference<Type>() {
                }));

        String encodedFunction = FunctionEncoder.encode(function);

// 如下為 ERC20 Token 標(biāo)準(zhǔn)接口：-----------
 // ERC20 Token Standard Interface
 // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
 // ----------------------------------------------------------------------------
contract ERC20 {
      function name() constant returns (string name)
      function symbol() constant returns (string symbol)
      function decimals() constant returns (uint8 decimals)
      function totalSupply() constant returns (uint totalSupply);
      function balanceOf(address _owner) constant returns (uint balance);
      function transfer(address _to, uint _value) returns (bool success);
      function transferFrom(address _from, address _to, uint _value) returns (bool success);
      function approve(address _spender, uint _value) returns (bool success);
      function allowance(address _owner, address _spender) constant returns (uint remaining);
      event Transfer(address indexed _from, address indexed _to, uint _value);
      event Approval(address indexed _owner, address indexed _spender, uint _value);
}

java／Android調(diào)用合約的transfer方法

這種方法不需要使用web3j封裝的方法拙泽，而是直接調(diào)用solidity合約的方法。

步驟
1移稳、web3j加載一個(gè)已經(jīng)部署的合約
2都许、驗(yàn)證合約是否加載成功isValid
3桨仿、如何加載合約成功伴嗡，則調(diào)用合約的transfer方法

  /**
     * ERC-20Token交易（調(diào)用solidity合約方式） 推薦使用
     *
     * @param contractAddress 合約地址
     * @param to              收款地址
     * @param value           轉(zhuǎn)賬金額
     * @param privateKey      私鑰
     * @throws ExecutionException
     * @throws InterruptedException
     */
    public void transferERC20Token(String contractAddress,
                                   String to,
                                   BigInteger value,
                                   String privateKey) throws ExecutionException, InterruptedException {

        //加載轉(zhuǎn)賬所需的憑證，用私鑰
        Credentials credentials = Credentials.create(privateKey);

        TokenERC20 contract = TokenERC20.load(
                contractAddress, web3j, credentials, Contract.GAS_PRICE, Contract.GAS_LIMIT);

        TransactionReceipt transactionReceipt = contract.transfer(to, value).sendAsync().get();
        String transactionHash = transactionReceipt.getTransactionHash();
        Log.i(TAG, "transferERC20Token transactionHash : " + transactionHash);
    }

注意：
1、這里的TokenERC20是根據(jù)solidity智能合約生成的對(duì)應(yīng)的Java類，用于java／Android和智能合約交互的，如果你對(duì)這里不太清楚，不妨看看我之前的一篇文章浅碾。
以太坊Web3j命令行生成Java版本的智能合約

2埂陆、如果加載合約失敗鹃栽，可能的一個(gè)原因是合約對(duì)應(yīng)的Java類中的BINARY的值不對(duì)蓬抄，這個(gè)值是你部署合約成功之后的bytecode阅爽，你最好檢查對(duì)比一下。

我發(fā)送一筆交易仍翰，可以通過這個(gè)地址查詢
https://rinkeby.etherscan.io/tx/0x05bd947e73068badbd9937854169f020980795da8a8182a67e9c2c1888f1874d