Java与智能合约交互（Web3j）- write函数
Posted MrLiuBai
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说在前头
Web3是一种新兴的网络概念，由于某些原因导致我们能够接触到的相关技术知识实在有限，每当我遇见技术瓶颈总是不能找到充足的资料，这也让我萌生了填补这片空白知识的冲动。“Hello Web3” 这个专栏会尽力将我掌握的web3 知识分享给大家。如果分享的知识能帮助到大家，希望能够 关注、点赞 支持作者！
本人已在github上发布Web3j工具，欢迎使用和star
Java与智能合约交互（Web3j）
之所以选择利用java与智能合约进行交互，完全是因为本人只会Java，并且Java是世界上最好的语言。
能干什么
- 监控合约状态，读取合约的关键参数，可作为后台数据源。
- 转账、授权等基础交互。
- 实现例如抢购、提挖买等复杂交互。
代码分享
- 引入依赖
<dependency>
<groupId>org.web3j</groupId>
<artifactId>core</artifactId>
<version>5.0.0</version>
</dependency>
- 新建Web3j对象
Web3j web3 = Web3j.build(new HttpService(rpcUrl));
- rpcUrl变量是区块链网络节点的url链接，这些节点会提供很多标准的api方法通过该url进行调用，web3j模块就是在此api上进行封装。
- 不同网络的rpcUrl可以在对应的区块链浏览器api文档上找到，百度关键字也很容易获取。
- 查询当前网络的gasPrice
// 获取gasPrice方法
BigInteger gasPrice = web3.ethGasPrice().send().getGasPrice();
/**
* 获取当期的gasPrice,如果超过最大的限制，取最大限制
*
* @return 在区间内的gasPrice
* @throws IOException 与节点交互出现异常
*/
public BigInteger getGasPriceWithLimit() throws IOException
BigInteger gasPrice = web3.ethGasPrice().send().getGasPrice();
log.info("Gas price: Gwei, Min gas price: Gwei, Max gas price: Gwei",
Convert.fromWei(String.valueOf(gasPrice), Convert.Unit.GWEI),
Convert.fromWei(String.valueOf(minGasPrice), Convert.Unit.GWEI),
Convert.fromWei(String.valueOf(maxGasPrice), Convert.Unit.GWEI));
// 超过最大限制返回最大的gasPrice
if (maxGasPrice.compareTo(gasPrice) < 0)
return maxGasPrice;
// 小于最小的限制返回最小的gasPrice
if (minGasPrice.compareTo(gasPrice) > 0)
return minGasPrice;
return gasPrice;
- 注意，该方法会获取近几个区块的gasPrice均值，可能偏高。
- 参考作者的getGasPriceWithLimit方法，如果你不是抢购之类紧急的需求，建议不要直接使用这个方法的返回值作为gasPrice，不然亏哭你！
- 查询当前账户交易笔数用于作为交易nonce
/**
* 获取交易数量
*
* @return 账户交易次数
* @throws IOException 与节点交互失败
*/
public BigInteger getTransactionCount() throws IOException
EthGetTransactionCount ethGetTransactionCount = web3.ethGetTransactionCount(
ownerAddress, DefaultBlockParameterName.LATEST).send();
return ethGetTransactionCount.getTransactionCount();
- 以太坊虚拟机用这个nonce字段作为顺序来处理你的多个交易，默认一般nonce取账户的交易笔数
- 本次交易nonce比上笔成功的交易还小的话会导致交易失败
- 查询当前区块链网络的链的chainId
long chainId = web3.ethChainId().send().getChainId().longValue();
- 在以太坊经典从以太坊分叉出来后，为了防止双花攻击，Chain ID在EIP155被引入。
- 通过在签名信息中加入Chain ID， 避免一个交易在签名之后被重复在不同的链上提交。
- 导入私钥（代码中的私钥切勿传到github公有仓库！！！）
Credentials credentials = Credentials.create(privateKey);
// 私钥对应的地址
String address = credentials.getAddress();
- 估算、签名、发送交易数据
/**
* 与合约交互
*
* @param contractAddress 交互合约地址
* @param functionName 交互函数名称
* @param value 携带的eth数量(单位Ether)
* @param input 输入参数 eg:Arrays.asList(new Address("0x6dF655480F465DC36347a5616E875D155804F0c5"), new Uint256(10000000));
* @param output 输出参数类型 eg: Arrays.asList(new TypeReference<Bool>());
* 类型映射关系
* boolean - bool
* BigInteger - uint/int
* byte[] - bytes
* String - string and address types
* List - dynamic/static array
* T - struct/tuple types
* @return 交易hash
* @throws Exception 与节点交互出现异常
*/
public String writeContract(String contractAddress, String functionName, String value, List<Type> input, List<TypeReference<?>> output) throws Exception
// 转换value的单位
BigInteger valueWei = Convert.toWei(value, Convert.Unit.ETHER).toBigInteger();
// 生成需要调用函数的data
Function function = new Function(functionName, input, output);
String data = FunctionEncoder.encode(function);
// 估算gasLimit
BigInteger gasLimit = estimateGasLimit(contractAddress, data, valueWei);
// 获取gasPrice
BigInteger gasPrice = getGasPriceWithLimit();
// 获取chainId
long chainId = web3.ethChainId().send().getChainId().longValue();
// 正式请求
RawTransaction rawTransaction = RawTransaction.createTransaction(getNonce(), gasPrice, gasLimit, contractAddress, valueWei, data);
// 签名数据
byte[] signedMessage = TransactionEncoder.signMessage(rawTransaction, chainId, credentials);
String hexValue = Numeric.toHexString(signedMessage);
// 发送数据
EthSendTransaction response = web3.ethSendRawTransaction(hexValue).send();
// 查看是否有错误
if (response.hasError())
throw new Exception("trade hash: " + response.getTransactionHash() +
"\\nerror: " + response.getError().getMessage());
log.info("function: data: ", functionName, data);
log.info("Gas fee: ETH", Convert.fromWei(String.valueOf(gasLimit.multiply(gasPrice)), Convert.Unit.ETHER));
log.info("Trade Hash: ", response.getTransactionHash());
return response.getTransactionHash();
/**
* 估算GasLimit
*
* @param to 发送的地址
* @param data 发送的数据
* @param value 携带的eth数量(单位wei)
* @return GasLimit
* @throws Exception 与节点交互失败
*/
public BigInteger estimateGasLimit(String to, String data, BigInteger value) throws Exception
if (gasLimit.intValue() != 0)
return gasLimit;
Transaction testTransaction = Transaction.createFunctionCallTransaction(ownerAddress, null, null, null, to, value, data);
EthEstimateGas response = web3.ethEstimateGas(testTransaction).send();
// 查看是否有错误
if (response.hasError())
throw new Exception("error: " + response.getError().getMessage());
return response.getAmountUsed();
- writeContract函数的相关参数说明请参考上一篇文章《read函数》
- estimateGasLimit函数用于计算本次执行的交易需要耗费的Gas数量，实际就是把你的交易数据传到链上模拟执行函数但不提交结果，将模拟执行花费的Gas作为请求结果返回
- 当拿到交易所需的所有数据，需要用私钥对数据进行签名操作方可执行
- 调用写函数执行转账操作
/**
* 转账操作
*
* @param contractAddress 交互合约地址
* @param recipient 接收转账地址
* @param amount 转账数量
* @return 交易hash
* @throws Exception 与节点交互失败
*/
public String transfer(String contractAddress, String recipient, String amount) throws Exception
List input = Arrays.asList(new Address(recipient)
, new Uint256(new BigInteger(amount, 10)));
List output = Arrays.asList(new TypeReference<Bool>()
);
return writeContract(contractAddress, "transfer", input, output);
掌握这些知识点最好的方法是自己将代码跑起来，去链上获取你想获取的信息
欢迎关注本专栏，作者知无不言~
以太坊智能合约部署与交互
启动容器来执行geth命令
[email protected]:~# docker run -i blockchain101/ethereum-geth:1.6.5 geth attach http://45.32.252.88:8201 Welcome to the Geth JavaScript console! instance: Geth/01/v1.6.5-stable/linux-amd64/go1.8 coinbase: 0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a at block: 6064 (Wed, 02 Aug 2017 01:13:50 UTC) datadir: /ethcluster/779977/data/01 modules: admin:1.0 eth:1.0 net:1.0 rpc:1.0 web3:1.0
查看我们的账户和余额
eth.getBalance(eth.accounts[0]) 11000000000000000000 eth.getBalance(eth.accounts[1]) 0 eth.accounts[0] "0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a" eth.accounts[1] "0xe82e2f0a5abd8774767b9751659976f9c4f59181"
发起一笔交易
>
eth.sendTransaction({from:eth.accounts[0],to:eth.accounts[1],value:web3.toWei(3,‘ether‘)}) "0x0075da712d26aea17d6647035107f509e13eaf3d113c1577db14d4cc4216caec"
查看交易细节
> eth.getTransaction("0x0075da712d26aea17d6647035107f509e13eaf3d113c1577db14d4cc4216caec") { blockHash: "0x3115703894dc6015c96ef4de3e5615f416498ca1f985902b38cd70e27dab8871", blockNumber: 1250, from: "0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a", gas: 90000, gasPrice: 18000000000, hash: "0x0075da712d26aea17d6647035107f509e13eaf3d113c1577db14d4cc4216caec", input: "0x", nonce: 0, r: "0x2aef2c1fa03a0fa4172d21e3383d8c0431d45ec855b9d16efdd5eb2de90c414c", s: "0xc4d530fb7902bf509fe56bfbea4861bf6cc16791afc9c9103c1a18f77407d1f", to: "0xe82e2f0a5abd8774767b9751659976f9c4f59181", transactionIndex: 0, v: "0x17cdb6", value: 3000000000000000000 } > eth.getBalance(eth.accounts[1]) 3000000000000000000
验证用户0的余额
> eth.getBalance(eth.accounts[0]) 7999622000000000000
编写一个简单的合约
contract Sample { uint public value; function Sample(uint v){ value=v; } function set(uint v){ value=v; } function get() constant returns (uint){ return value; } }
在remix网页编译得到ABI接口和合约的二进制代码、
abi=[{"constant":true,"inputs":[],"name":"value","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},
{"constant":false,"inputs":[{"name":"v","type":"uint256"}],"name":"set","outputs":[],"payable":false,"type":"function"},
{"constant":true,"inputs":[],"name":"get","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},
{"inputs":[{"name":"v","type":"uint256"}],"payable":false,"type":"constructor"}]
[{
constant: true,
inputs: [],
name: "value",
outputs: [{
name: "",
type: "uint256"
}],
payable: false,
type: "function"
}, {
constant: false,
inputs: [{
name: "v",
type: "uint256"
}],
name: "set",
outputs: [],
payable: false,
type: "function"
}, {
constant: true,
inputs: [],
name: "get",
outputs: [{
name: "",
type: "uint256"
}],
payable: false,
type: "function"
}, {
inputs: [{
name: "v",
type: "uint256"
}],
payable: false,
type: "constructor"
}]
需要使用eth.contract来定义一个合约类
> sample=eth.contract(abi) { abi: [{ constant: true, inputs: [], name: "value", outputs: [{...}], payable: false, type: "function" }, { constant: false, inputs: [{...}], name: "set", outputs: [], payable: false, type: "function" }, { constant: true, inputs: [], name: "get", outputs: [{...}], payable: false, type: "function" }, { inputs: [{...}], payable: false, type: "constructor" }], eth: { accounts: ["0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a", "0xe82e2f0a5abd8774767b9751659976f9c4f59181"], blockNumber: 6225, coinbase: "0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a", compile: { lll: function(), serpent: function(), solidity: function() }, defaultAccount: undefined, defaultBlock: "latest", gasPrice: 18000000000, hashrate: 0, mining: false, pendingTransactions: [], protocolVersion: "0x3f", syncing: false, call: function(), contract: function(abi), estimateGas: function(), filter: function(fil, callback), getAccounts: function(callback), getBalance: function(), getBlock: function(), getBlockNumber: function(callback), getBlockTransactionCount: function(), getBlockUncleCount: function(), getCode: function(), getCoinbase: function(callback), getCompilers: function(), getGasPrice: function(callback), getHashrate: function(callback), getMining: function(callback), getPendingTransactions: function(callback), getProtocolVersion: function(callback), getRawTransaction: function(), getRawTransactionFromBlock: function(), getStorageAt: function(), getSyncing: function(callback), getTransaction: function(), getTransactionCount: function(), getTransactionFromBlock: function(), getTransactionReceipt: function(), getUncle: function(), getWork: function(), iban: function(iban), icapNamereg: function(), isSyncing: function(callback), namereg: function(), resend: function(), sendIBANTransaction: function(), sendRawTransaction: function(), sendTransaction: function(), sign: function(), signTransaction: function(), submitTransaction: function(), submitWork: function() }, at: function(address, callback), getData: function(), new: function() }
合约的二进制代码赋值给SampleHEX方便使用
SampleHEX="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"
把合约代码部署上链
> thesample=sample.new(1,{from:eth.accounts[0],data:SampleHEX,gas:3000000}) { abi: [{ constant: true, inputs: [], name: "value", outputs: [{...}], payable: false, type: "function" }, { constant: false, inputs: [{...}], name: "set", outputs: [], payable: false, type: "function" }, { constant: true, inputs: [], name: "get", outputs: [{...}], payable: false, type: "function" }, { inputs: [{...}], payable: false, type: "constructor" }], address: undefined, transactionHash: "0xee74bcb4461c9712ec9aca96a5a3a4c3c64be1213854d519fc8e5432b554f7a1" }
查看交易细节
> samplerecpt=eth.getTransactionReceipt("0xee74bcb4461c9712ec9aca96a5a3a4c3c64be1213854d519fc8e5432b554f7a1") { blockHash: "0xddba16545af882835fb9a69a0e5f3b9287c61664837d5ea0068b38575cb665c5", blockNumber: 6246, contractAddress: "0x7504fa9d64ab290844b82660d43b310f8fba0276", cumulativeGasUsed: 141836, from: "0x4c57e7e9c2f728046ddc6e96052056a241bdbd0a", gasUsed: 141836, logs: [], logsBloom: "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", root: "0xd1093ecaca9cc0d10e82a533a15feccedf7ff5c79fb3ebd9366ec0b35dbef478", to: null, transactionHash: "0xee74bcb4461c9712ec9aca96a5a3a4c3c64be1213854d519fc8e5432b554f7a1", transactionIndex: 0 }
合约命名
> samplecontract=sample.at("0x7504fa9d64ab290844b82660d43b310f8fba0276") { abi: [{ constant: true, inputs: [], name: "value", outputs: [{...}], payable: false, type: "function" }, { constant: false, inputs: [{...}], name: "set", outputs: [], payable: false, type: "function" }, { constant: true, inputs: [], name: "get", outputs: [{...}], payable: false, type: "function" }, { inputs: [{...}], payable: false, type: "constructor" }], address: "0x7504fa9d64ab290844b82660d43b310f8fba0276", transactionHash: null, allEvents: function(), get: function(), set: function(), value: function() }
合约查看功能函数get（）,然后调用set()函数，再get()查看时已经改变了
samplecontract.get.call() 1 > samplecontract.set.sendTransaction(9, {from:eth.accounts[0], gas:3000000}) "0x822ee6fb4caceb7e844c533f7f3bc57806f7cb3676fb3066eb848cca46b2f38a" > samplecontract.get.call() 9
我们再打开一个终端，打开cluster1的peer02的控制台，直接at到上一个终端部署的智能合约地址并进行set操作
[email protected]:~/ethereum-docker/ethereum-docker/ethereum-testnet-docker/dockercomposefiles# docker run -i blockchain101/ethereum-geth:1.6.5 geth attach http://45.32.252.88:9201 Welcome to the Geth JavaScript console! > abi=[{"constant":true,"inputs":[],"name":"value","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"v","type":"uint256"}],"name":"set","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"get","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"inputs":[{"name":"v","type":"uint256"}],"payable":false,"type":"constructor"}] > sample=eth.contract(abi) SampleHEX="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"
直接把合约地址赋值并进行set操作
samplecontract=sample.at("0x7504fa9d64ab290844b82660d43b310f8fba0276") > samplecontract.get.call() 9
简单的方法来了。智能合约的部署需要编译，这里用在线编译：
https://ethereum.github.io/browser-solidity/#version=soljson-v0.4.14+commit.c2215d46.js
修改编译好的abi和对象名称：
这里在网上找了个代币的只能合约，可以进行充值、转账和查询，issue 函数可以向充值以太到合约账户，transfer 函数可以向其他账号发送token，getBalance 函数可以获取某个账号的token余额，代码如下： pragma solidity ^0.4.2; contract Token { address issuer; mapping (address => uint) balances; event Issue(address account, uint amount); event Transfer(address from, address to,uint amount); function Token() { issuer = msg.sender; } function issue(address account, uintamount) { if (msg.sender != issuer) throw; balances[account] += amount; } function transfer(address to, uint amount){ if (balances[msg.sender] < amount)throw; balances[msg.sender] -= amount; balances[to] += amount; Transfer(msg.sender, to, amount); } function getBalance(address account)constant returns (uint) { return balances[account]; } } 修改编译好的gas和对象名称： varbrowser_untitled_sol_tokenContract =web3.eth.contract([{"constant":false,"inputs":[{"name":"account","type":"address"},{"name":"amount","type":"uint256"}],"name":"issue","outputs":[],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"to","type":"address"},{"name":"amount","type":"uint256"}],"name":"transfer","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"account","type":"address"}],"name":"getBalance","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"inputs":[],"payable":false,"type":"constructor"},{"anonymous":false,"inputs":[{"indexed":false,"name":"account","type":"address"},{"indexed":false,"name":"amount","type":"uint256"}],"name":"Issue","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"from","type":"address"},{"indexed":false,"name":"to","type":"address"},{"indexed":false,"name":"amount","type":"uint256"}],"name":"Transfer","type":"event"}]); var token =browser_untitled_sol_tokenContract.new( { from: web3.eth.accounts[0], data:‘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‘, gas: ‘4300000‘ }, function (e, contract){ console.log(e, contract); if (typeof contract.address !==‘undefined‘) { console.log(‘Contract mined! address:‘ + contract.address + ‘ transactionHash: ‘ + contract.transactionHash); } })
此时输入合约部署的实例a_demotypes, 可以看到a_demotypes的详情。
控制台调用
> a_demotypes { abi: [{ constant: false, inputs: [{...}], name: "f", outputs: [{...}], payable: false, type: "function" }], address: "0x54ed7a5f5a63ddada3bfe83b3e632adabaa5fc2f", transactionHash: "0x69cde62bcd6458e14f40497f4840f422911d63f5dea2b3a9833e6810db64a1c9", allEvents: function(), f: function() }
这里重点就是address表示的是合约的地址，你会发现这个和账号的信息结果一样，其实你也可以把这个合约地址看做是一个账号地址，后面我们外部调用到的就是这个合约地址。
充值 token.issue.sendTransaction(eth.accounts[0],100, {from: eth.accounts[0]}); 发送 token token.transfer(eth.accounts[1], 30, {from:eth.accounts[0]}) 查看余额 token.getBalance() 控制台调用就不多说，和Java对象调用一样，直接调用即可
外部接口与智能合约交互
以太坊对外提供的有很多接口JSON RPC接口，web3接口，这里我们用JSON RPC接口。
相关API: https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sendrawtransaction
合约交互的原理
合约的交互都是一次交易，而我们要做的就是把要调用的方法和参数按照api规定的以参数的形式向区块请求一次交易，ethereum接收到我们的请求后通过解析传递的参数来执行相关的合约代码。
RPC接口给我们提供了俩个方法：eth_sendTransaction和eth_call。
eth_sendTransaction Createsnew message call transaction or a contract creation, if the data field containscode. Parameters Object - The transaction object from: DATA, 20 Bytes - The address the transaction is send from. to: DATA, 20 Bytes - (optional when creating new contract) The address the transaction is directed to. gas: QUANTITY - (optional, default: 90000) Integer of the gas provided for the transaction execution. It will return unused gas. gasPrice: QUANTITY - (optional, default: To-Be-Determined) Integer of the gasPrice used for each paid gas value: QUANTITY - (optional) Integer of the value send with this transaction data: DATA - The compiled code of a contract OR the hash of the invoked method signature and encoded parameters. For details see Ethereum Contract ABI nonce: QUANTITY - (optional) Integer of a nonce. This allows to overwrite your own pending transactions that use the same nonce.
可以看到，如果我们创建的为合约时，我们只需要from,to(文档上写的是可选的，但是实际操作中没有to为null的话合约不能正常执行，建议还是加上，这个值就是前面我们部署合约后生成的合约address),data。Data的属性的值具体可以看Contract ABI。这里大概说下：
Data的值相对来说不是固定的，具体怎么生成与合约的参数类型，参数数量都有关联。这里我们以部署的token合约的三个方法为例：
充值issue (address account, uint amount)
这个方法有俩个参数，address充值账号，uint充值数量。
根据Contract ABI，data值应该为方法名的sha3的前8个字节+参数的64字节，不够前面补充为0。
这里方法名并不是issue (address account, uint amount)而是issue(address,uint256)的sha3值。
web3.sha3("issue(address,uint256)")
"0x867904b44b606800f6f10498e11292d04ea19bfc7fe4bc0f1695aa516381f73d"
我们往第一个账号充值10，这里的数据不是以太币，而是我们自己创建的代币。
eth.accounts[0]
"0x0cc9684af605bae10de801218321c1336bb62946"
将10转换为16进制为
000000000000000000000000000000000000000000000000000000000000000a
那么data的数据为：
0x867904b4000000000000000000000000fdf57e81872562a6112656f961944ce821fdf7eb000000000000000000000000000000000000000000000000000000000000000a
那么最后我们调用eth_sendTransaction方法传递参数JSON对象为：
{ from:0xfdf57e81872562a6112656f961944ce821fdf7eb, to:0x7fe133950fc010ce41322d88f64f1918b9abb3a3, data: 0x867904b4000000000000000000000000fdf57e81872562a6112656f961944ce821fdf7eb000000000000000000000000000000000000000000000000000000000000000a }
返回：此交易的hash值,此时该交易还没有执行，只是创建，还需要矿工通过挖矿才能完成。
调用接口方法：
JsonRpcHttpClient client = newJsonRpcHttpClient(new URL(“http://127.0.0.1:8545”)); Object result = client.invoke(methodName,params, Object.class);
通过控制台查看第一个账号已有代币：
token.getbalance(eth.accounts[0])
执行调用接口代码。返回交易hash值：
此时控制台输入：
交易和充值一样，需要注意的是代币转出账号为from属性的值，代币转入账号为data属性里的值，to对应的是合约地址。
eth_call
Executes anew message call immediately without creating a transaction on the block chain. Parameters Object - The transaction call object from: DATA, 20 Bytes - (optional) The address the transaction is sent from. to: DATA, 20 Bytes - The address the transaction is directed to. gas: QUANTITY - (optional) Integer of the gas provided for the transaction execution. eth_call consumes zero gas, but this parameter may be needed by some executions. gasPrice: QUANTITY - (optional) Integer of the gasPrice used for each paid gas value: QUANTITY - (optional) Integer of the value send with this transaction data: DATA - (optional) Hash of the method signature and encoded parameters. For details seeEthereum Contract ABI QUANTITY|TAG - integer block number, or the string "latest", "earliest" or "pending", see the default block parameter
这个方法返回一条信息给我们，相当于数据库的查询功能，参数也是三个，from,to,data，数据格式都是一样的。
查询getBalance(address account)
查询方法hash码：
web3.sha3("getBalance(address)")
"0xf8b2cb4f3943230388faeee074f1503714bff212640051caba01411868d14ae3"
查询我们上一步充值的账号，那么传递的参数data为：
0xf8b2cb4f000000000000000000000000fdf57e81872562a6112656f961944ce821fdf7eb
eth_call方法最后参数为：
{ from: 0xfdf57e81872562a6112656f961944ce821fdf7eb, to:0x7fe133950fc010ce41322d88f64f1918b9abb3a3, data:0xf8b2cb4f000000000000000000000000fdf57e81872562a6112656f961944ce821fdf7eb }
注意，这个方法需要俩参数，处理一个JSONobject外，还有一个字符串参数，这俩可以为“”或者”latest”, “earliest” or “pending”
调用接口返回一个16进制字符串：
0x0000000000000000000000000000000000000000000000000000000000000071就是该账号的代币数量，转换为十进制为：113，与控制查询一致。
这就是一个智能合约的交互过程。是不是很简单啊。
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