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：

org.web3j

core

3.2.0

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() {

}));

//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;

}

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;

}

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];

}

}