java开发区块链4

原文地址为： java开发区块链4

使用java开发区块链

这里需要使用的环境 web3j，nodejs

安装编译sol工具

$ npm install -g solc

保存为hello.sol文件到本地

pragma solidity 0.4.19;  
contract hello {  
function main(uint a) constant returns (uint b)   
    {  
        uint result = a * 8;  
return result;  
    }  
}

编译sol文件

$ solcjs <sol文件目录>   --optimize  --bin --abi --output-dir <输出目录>

//demo
$ solcjs F:\\hello.sol   --optimize  --bin --abi --output-dir F:\\

出现这种错误

Failed to write F:\F_\hello_sol_hello.bin: Error: ENOENT: no such file or directory, open 'F:\F_\hello_sol_hello.bin'
Failed to write F:\F_\hello_sol_hello.abi: Error: ENOENT: no such file or directory, open 'F:\F_\hello_sol_hello.abi'

这里有个坑，就是使用solcjs 编译智能合约文件输出到目录会有一个文件夹，这个需要手动创建，我这里输出目录到F:\\ 但是它还是要输出到F:\\F_\ 下，这里的F_文件夹需要我们创建！

编译成功,记录下bin 和 abi后缀的文件
使用web3j工具生成java版本的智能合约
web3j 命令行工具下载

$ web3j solidity generate <编译的bin文件地址> <编译的abi文件地址> -o <输出目录> -p <java包名>
//demo
$ web3j solidity generate F:\F_\hello_sol_hello.bin F:\F_\hello_sol_hello.abi -o E:\etheth\src\main\java -p xyz.lihang.demo.eth.sol

生成成功

package xyz.lihang.demo.eth.sol;

import java.math.BigInteger;
import java.util.Arrays;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.Function;
import org.web3j.abi.datatypes.Type;
import org.web3j.abi.datatypes.generated.Uint256;
import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.RemoteCall;
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 3.2.0.
 */
public class Hello_sol_hello extends Contract {
private static final String BINARY = "60606040523415600e57600080fd5b609a8061001c6000396000f300606060405260043610603e5763ffffffff7c0100000000000000000000000000000000000000000000000000000000600035041663ab3ae25581146043575b600080fd5b3415604d57600080fd5b60566004356068565b60405190815260200160405180910390f35b600802905600a165627a7a723058200cc51f5dad45190b24189d9f8ff836d704bcebc9862cfd669e054b8c8f19f66c0029";

protected Hello_sol_hello(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

protected Hello_sol_hello(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }

public RemoteCall<BigInteger> main(BigInteger a) {
        Function function = new Function("main", 
                Arrays.<Type>asList(new org.web3j.abi.datatypes.generated.Uint256(a)), 
                Arrays.<TypeReference<?>>asList(new TypeReference<Uint256>() {}));
return executeRemoteCallSingleValueReturn(function, BigInteger.class);
    }

public static RemoteCall<Hello_sol_hello> deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
return deployRemoteCall(Hello_sol_hello.class, web3j, credentials, gasPrice, gasLimit, BINARY, "");
    }

public static RemoteCall<Hello_sol_hello> deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
return deployRemoteCall(Hello_sol_hello.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, "");
    }

public static Hello_sol_hello load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
return new Hello_sol_hello(contractAddress, web3j, credentials, gasPrice, gasLimit);
    }

public static Hello_sol_hello load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
return new Hello_sol_hello(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
    }
}

一定要注意合约调用后进行挖矿，这样才能网络确认，才能使用合约

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使用java开发区块链

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