用web3j實現與智慧合約互動
阿新 • • 發佈：2019-02-14
之前一直用nodejs呼叫web3.js與智慧合約互動，但是沒找到與Java專案進行互動的方法。原來以太坊是有Java介面web3j的。
本文實現：
1、將資料存在ipfs上面，獲取hash，將hash存在區塊鏈上面。
2、從區塊鏈上獲取hash，通過hash從ipfs上的資料取下來。
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環境配置：
首先將web3j和ipfs的jar包匯入專案（參考最上面的文件即可），或者下載下來自己匯入，下載地址：
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1、用geth搭建一條私有鏈，建立一個賬戶，進行挖礦獲得一些ether，下面部署或載入合約的時候會用到這個賬戶。
2、建立一個只能合約：
pragma solidity ^0.4.17; contract Data{ string public data; function Data()public{ data = ""; } function setData(string str) public payable{ data = str; } function getData() public view returns (string) { return data; } }
3、編譯，生成java檔案
solcjs Data.sol --abi --bin -o ./此時生成了Data_sol_Data.abi檔案和Data_sol_Data.bin檔案，下面命令用到這兩個檔案
web3j solidity generate --solidityTypes <智慧合約編譯之後的.bin檔案的地址>.bin <智慧合約編譯之後的.abi檔案的地址>.abi -o /path/to/src/main/java -p com.your.organisation.name-o 後接生成好的java檔案放置的位置，-p 後接生成的java檔案的包名
（web3j是個命令列工具，安裝方法最上面文件中有，我用的linux，使用的是解壓包中的web3j）
將Java檔案直接生成在Java專案中，或者生成後複製過去改一下包名。下面是自動生成的Java檔案：
package test_eth;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collections;
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;
/**
* <p>Auto generated code.
* <p><strong>Do not modify!</strong>
* <p>Please use the <a href="https://docs.web3j.io/command_line.html">web3j command line tools</a>,
* or the org.web3j.codegen.SolidityFunctionWrapperGenerator in the
* <a href="https://github.com/web3j/web3j/tree/master/codegen">codegen module</a> to update.
*
* <p>Generated with web3j version 3.3.1.
*/
public class Data_sol_Data extends Contract {
private static final String BINARY = "6060604052341561000f57600080fd5b6040805190810160405280600981526020017f696e6974206461746100000000000000000000000000000000000000000000008152506000908051906020019061005a929190610060565b50610105565b828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f106100a157805160ff19168380011785556100cf565b828001600101855582156100cf579182015b828111156100ce5782518255916020019190600101906100b3565b5b5090506100dc91906100e0565b5090565b61010291905b808211156100fe5760008160009055506001016100e6565b5090565b90565b61040f806101146000396000f300606060405260043610610057576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff1680633bc5de301461005c57806347064d6a146100ea57806373d4a13a1461013c575b600080fd5b341561006757600080fd5b61006f6101ca565b6040518080602001828103825283818151815260200191508051906020019080838360005b838110156100af578082015181840152602081019050610094565b50505050905090810190601f1680156100dc5780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b61013a600480803590602001908201803590602001908080601f01602080910402602001604051908101604052809392919081815260200183838082843782019150505050505091905050610272565b005b341561014757600080fd5b61014f61028c565b6040518080602001828103825283818151815260200191508051906020019080838360005b8381101561018f578082015181840152602081019050610174565b50505050905090810190601f1680156101bc5780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b6101d261032a565b60008054600181600116156101000203166002900480601f0160208091040260200160405190810160405280929190818152602001828054600181600116156101000203166002900480156102685780601f1061023d57610100808354040283529160200191610268565b820191906000526020600020905b81548152906001019060200180831161024b57829003601f168201915b5050505050905090565b806000908051906020019061028892919061033e565b5050565b60008054600181600116156101000203166002900480601f0160208091040260200160405190810160405280929190818152602001828054600181600116156101000203166002900480156103225780601f106102f757610100808354040283529160200191610322565b820191906000526020600020905b81548152906001019060200180831161030557829003601f168201915b505050505081565b602060405190810160405280600081525090565b828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f1061037f57805160ff19168380011785556103ad565b828001600101855582156103ad579182015b828111156103ac578251825591602001919060010190610391565b5b5090506103ba91906103be565b5090565b6103e091905b808211156103dc5760008160009055506001016103c4565b5090565b905600a165627a7a72305820c88de5343e43686be6997856d3a1239da233f21f97cf4a51b590864fd723010c0029";
protected Data_sol_Data(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
}
protected Data_sol_Data(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
}
public RemoteCall<String> getData() {
final Function function = new Function("getData",
Arrays.<Type>asList(),
Arrays.<TypeReference<?>>asList(new TypeReference<Utf8String>() {}));
return executeRemoteCallSingleValueReturn(function, String.class);
}
public RemoteCall<TransactionReceipt> setData(String str, BigInteger weiValue) {
final Function function = new Function(
"setData",
Arrays.<Type>asList(new org.web3j.abi.datatypes.Utf8String(str)),
Collections.<TypeReference<?>>emptyList());
return executeRemoteCallTransaction(function, weiValue);
}
public RemoteCall<String> data() {
final Function function = new Function("data",
Arrays.<Type>asList(),
Arrays.<TypeReference<?>>asList(new TypeReference<Utf8String>() {}));
return executeRemoteCallSingleValueReturn(function, String.class);
}
public static RemoteCall<Data_sol_Data> deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
return deployRemoteCall(Data_sol_Data.class, web3j, credentials, gasPrice, gasLimit, BINARY, "");
}
public static RemoteCall<Data_sol_Data> deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
return deployRemoteCall(Data_sol_Data.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, "");
}
public static Data_sol_Data load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
return new Data_sol_Data(contractAddress, web3j, credentials, gasPrice, gasLimit);
}
public static Data_sol_Data load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
return new Data_sol_Data(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
}
}
4、編寫與ipfs互動的程式碼IpfsFile.java：
package test_eth;
import java.io.IOException;
import io.ipfs.api.IPFS;
import io.ipfs.api.MerkleNode;
import io.ipfs.api.NamedStreamable;
public class IpfsFile {
public static String add(String data) throws IOException {
IPFS ipfs = new IPFS("/ip4/127.0.0.1/tcp/5001");
NamedStreamable.ByteArrayWrapper file = new NamedStreamable.ByteArrayWrapper(data.getBytes());
MerkleNode hash = ipfs.add(file).get(0);
return hash.hash.toString();
}
public static String get(String hash) throws IOException {
IPFS ipfs = new IPFS("/ip4/127.0.0.1/tcp/5001");
MerkleNode md = new MerkleNode(hash);
byte[] data = ipfs.cat(md.hash);
return new String(data);
}
// public static void main(String []argv) {
// try {
// String hash = add("\"name\":\"zhj\"");
// System.out.println("hash:"+hash);
//
// String data = get(hash);
// System.out.println("data:"+data);
// } catch (IOException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
// }
}5、編寫blockchain-ipfs互動程式碼dataOperator.java：
package test_eth;
import java.io.IOException;
import org.web3j.crypto.CipherException;
import org.web3j.crypto.Credentials;
import org.web3j.crypto.WalletUtils;
import org.web3j.protocol.Web3j;
public class dataOperator {
// get hash form blockchain, then get data from ipfs using the hash
public String getData(Web3j web3j) throws Exception {
Credentials credentials = WalletUtils.loadCredentials(Consts.PASSWORD, Consts.PATH);
String address = Consts.ADDRESS;
Data_sol_Data dataOp = Data_sol_Data.load(Consts.ADDRESS, web3j, credentials, Consts.GAS_PRICE,
Consts.GAS_LIMIT);
String ipfs_hash = dataOp.getData().send();
String data = IpfsFile.get(ipfs_hash);
return data;
}
// set data to ipfs and get a hash, the save the hash to blockchain
public Boolean setData(Web3j web3j, String data) throws Exception {
Credentials credentials = WalletUtils.loadCredentials(Consts.PASSWORD, Consts.PATH);
String address = Consts.ADDRESS;
Data_sol_Data dataOp = Data_sol_Data.load(Consts.ADDRESS, web3j, credentials, Consts.GAS_PRICE,
Consts.GAS_LIMIT);
String ipfs_hash = IpfsFile.add(data);
dataOp.setData(ipfs_hash, Consts.GAS_VALUE).send();
return true;
}
}上面沒有部署合約，直接載入之前部署好的。如果還沒有部署，可以使用Data_sol_Data.deploy()函式來部署，只部署一次記錄下合約的地址，以後呼叫前直接載入已經部署好的就可以了。
(補充:上面連線鏈的方式是不安全的,因為沒有指定chain_id,所以有可能會將資訊廣播到其他鏈上,可以通過下面的方式來制定id:
TransactionManager transactionManager = new RawTransactionManager(web3j, credentials, Consts.CHAINID);
dataOp = DataOperatorContract.load(address, web3j, transactionManager, Consts.GAS_PRICE, Consts.GAS_LIMIT);
其中用到的常量寫在一個Consts.java檔案中：
package test_eth;
import java.math.BigInteger;
public class Consts {
// GAS價格
public static BigInteger GAS_PRICE = BigInteger.valueOf(20_000_000_000L);
// GAS上限
public static BigInteger GAS_LIMIT = BigInteger.valueOf(4_300_000L);
// 交易費用
public static BigInteger GAS_VALUE = BigInteger.valueOf(100_000L);;
// 賬戶密碼
public static String PASSWORD = "123";
// 賬戶檔案路徑
public static String PATH = "/home/zhj/project/test_chain/web3j/keystore/UTC--2018-03-25T08-56-52.659408004Z--5daa1392dc380cbbd7fb86614514c80bb7b54424";
// 合約地址，第一次部署之後記錄下來
public static String ADDRESS = "0x9bc65f8c4F3Dc31436E561CD6D893669710225e2";
public static byte CHAINID = (byte) 1234; //chain id,在創世區塊中定義的
}
6、測試入口：
package test_eth;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.http.HttpService;
public class test {
public static void main(String[] argv) {
try {
Web3j web3j = Web3j.build(new HttpService("http://localhost:8545"));
dataOperator dataOp = new dataOperator();
String data = "";
// set data and get data
dataOp.setData(web3j, "fly");
data = dataOp.getData(web3j);
System.out.println("Data:" + data);
} catch (Exception e) {
e.printStackTrace();
}
}
}
7、執行：
啟動ipfs，命令列輸入：ipfs daemon
進入geth console介面，進行挖礦（如果挖礦卡，可以只在部署合約和setData的時候進行挖礦）
（本文中只實現了一些簡單的功能，複雜操作參考官方文件）