ERC20代币转账以及余额查询--java(web3j)_查询合约地址的某个token余额 web3j java

ERC20代币转账以及余额查询–java(web3j)

准备工作：转账之前你得有一个ERC20代币，代币发行戳这里，可以在测试网上进行测试。
因为发行代币本质就是部署智能合约，是需要消耗gas的，代币转账也是需要消耗eth作为手续费的。
准备工作完成之后，就让我们直接进行ERC20代币转账吧～
通过调用web3j的API完成相关操作，所需maven依赖：

<dependency>
    <groupId>org.web3j</groupId>
    <artifactId>core</artifactId>
    <version>3.2.0</version>
</dependency>
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一：代币转账

该代币转账是通过构建原始交易的方式进行的，请看代码，主网亲测有效～

/**
     * erc20代币转账
     *
     * @param from            转账地址
     * @param to              收款地址
     * @param value           转账金额
     * @param privateKey      转账这私钥
     * @param contractAddress 代币合约地址
     * @return 交易哈希
     * @throws ExecutionException
     * @throws InterruptedException
     * @throws IOException
     */
    public static String transferERC20Token(String from, String to, BigInteger value, String privateKey, String contractAddress) throws ExecutionException, InterruptedException, IOException {
        Web3j web3j = Web3j.build(new HttpService("https://mainnet.infura.io/v3/c313bf2c97834ee29d933a996caaafb0"));
        //加载转账所需的凭证，用私钥
        Credentials credentials = Credentials.create(privateKey);
        //获取nonce，交易笔数
        BigInteger nonce;
        EthGetTransactionCount ethGetTransactionCount = web3j.ethGetTransactionCount(from, DefaultBlockParameterName.PENDING).send();
        if (ethGetTransactionCount == null) {
            return null;
        }
        nonce = ethGetTransactionCount.getTransactionCount();
        //gasPrice和gasLimit 都可以手动设置
        BigInteger gasPrice;
        EthGasPrice ethGasPrice = web3j.ethGasPrice().sendAsync().get();
        if (ethGasPrice == null) {
            return null;
        }
        gasPrice = ethGasPrice.getGasPrice();
        //BigInteger.valueOf(4300000L) 如果交易失败 很可能是手续费的设置问题
        BigInteger gasLimit = BigInteger.valueOf(60000L);
        //ERC20代币合约方法
        value = value.multiply(VALUE);
        Function function = new Function(
                TRANSFER,
                Arrays.asList(new Address(to), new Uint256(value)),
                Collections.singletonList(new TypeReference<Type>() {
                }));
        //创建RawTransaction交易对象
        String encodedFunction = FunctionEncoder.encode(function);
        RawTransaction rawTransaction = RawTransaction.createTransaction(nonce, gasPrice, gasLimit,
                contractAddress, encodedFunction);

        //签名Transaction
        byte[] signMessage = TransactionEncoder.signMessage(rawTransaction, credentials);
        String hexValue = Numeric.toHexString(signMessage);
        //发送交易
        EthSendTransaction ethSendTransaction = web3j.ethSendRawTransaction(hexValue).sendAsync().get();
        String hash = ethSendTransaction.getTransactionHash();
        if (hash != null) {
            return hash;
        }
        return null;
    }
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二：代币余额查询

private static final String DATA_PREFIX = "0x70a08231000000000000000000000000";
public static BigDecimal getBalance(String address, String contractAddress) throws IOException {
        String value = Admin.build(new HttpService("https://mainnet.infura.io"))
                .ethCall(org.web3j.protocol.core.methods.request.Transaction.createEthCallTransaction(address,
                contractAddress, DATA_PREFIX + address.substring(2)), DefaultBlockParameterName.PENDING).send().getValue();
        String s = new BigInteger(value.substring(2), 16).toString();
        BigDecimal balance = new BigDecimal(s).divide(WEI, 6, RoundingMode.HALF_DOWN);
        return balance;
    }
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以上代码主网发行的代币亲测有效，如果对您有帮助，就点个赞吧～

最后，附上简单的ERC20代币合约

pragma solidity ^0.4.25;

contract ERC20Interface {

    string public constant name = "测试币";
    string public constant symbol = "CSB";
    uint8 public constant decimals = 18;

    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

contract SafeMath {

    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
        if (a == 0) {
            return 0;
        }
        c = a * b;
        assert(c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
        c = a + b;
        assert(c >= a);
        return c;
    }
}


contract CSBToken is ERC20Interface, SafeMath {

  string public name;
  string public symbol;
  uint8 public decimals;
  uint256 public totalSupply;


  mapping (address => uint256) public balanceOf;

  mapping (address => mapping (address => uint256)) public allowanceOf;

   constructor() public payable {
      name = "测试币";
      symbol = "CSB";
      decimals = 18;
      totalSupply = 1000000000 * 10 ** uint256(decimals);
      balanceOf[msg.sender] = totalSupply;
   }

    function _transfer(address _from, address _to, uint _value) internal {
       require(_to != 0x0);
       require(balanceOf[_from] >= _value);
       require(balanceOf[_to] + _value > balanceOf[_to]);
       uint previousBalances = balanceOf[_from] + balanceOf[_to];
       balanceOf[_from] -= _value;
       balanceOf[_to] += _value;
      emit Transfer(_from, _to, _value);
       assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
       _transfer(msg.sender, _to, _value);
       return true;
   }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
       require(allowanceOf[_from][msg.sender] >= _value);
       allowanceOf[_from][msg.sender] -= _value;
       _transfer(_from, _to, _value);
       return true;
   }

    function approve(address _spender, uint256 _value) public returns (bool success) {
       allowanceOf[msg.sender][_spender] = _value;
      emit Approval(msg.sender, _spender, _value);
       return true;
   }

   function allowance(address _owner, address _spender) view public returns (uint remaining){
     return allowanceOf[_owner][_spender];
   }

  function totalSupply() public constant returns (uint totalsupply){
      return totalSupply;
  }

  function balanceOf(address tokenOwner) public constant returns(uint balance){
      return balanceOf[tokenOwner];
  }

}
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