java玩轉區塊鏈-基礎篇-環境搭建

可以不讓搞，但是不允許你不會

java環境配置

1. jdk版本，jdk1.8+；
2. IDE環境，ideas；
3. 依賴包，web3；
4. 區塊鏈網路，開發網，Ganache；

基礎概念

區塊鏈網路: 提供區塊鏈交易的網路，測驗網和正式網由以太坊提供，開發網路可以本地安裝，ganache，Hardhat是兩個可以本地安裝的區塊鏈服務器，ganache是本教程使用的開發區塊鏈服務器，
web3：與區塊鏈進行互動的網路協議，web3目前有python，nodejs，java，typeScript等語言實作
gas：交易手續費，就是我們所說的（挖礦）費，區塊鏈上的所有操作都由網路帶寬存盤的成本，這部分費用需要由交易方提供

java環境搭建

jdk1.8

ideas創建java專案引導

file—>New—>Project

ideas創建java專案,命名 ethJavaLession01

maven包參考

<dependency>
   <groupId>org.web3j</groupId>
    <artifactId>core</artifactId>
    <version>5.0.0</version>
</dependency>
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>
<repositories>
	<repository>
        <id>central</id>
        <name>central</name>
        <url>https://maven.aliyun.com/repository/central</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
    </repository>
    <repository>
        <id>jcenter</id>
        <name>jcenter</name>
        <url>http://jcenter.bintray.com/</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
    </repository>
    <repository>
        <id>maven-net-cn</id>
        <name>Maven China Mirror</name>
        <url>https://dl.bintray.com/ethereum/maven</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
    </repository>
</repositories>

java代碼

package com.eth;

import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.methods.response.EthBlockNumber;
import org.web3j.protocol.core.methods.response.EthGasPrice;
import org.web3j.protocol.core.methods.response.Web3ClientVersion;
import org.web3j.protocol.http.HttpService;

import java.io.IOException;

public class EthTest {
    public static void main(String[] args) {
        System.out.println("Connecting to Ethereum ...");
        Web3j web3 = Web3j.build(new HttpService("HTTP://127.0.0.1:7545"));
        System.out.println("Successfuly connected to Ethereum");
        try {
            // web3_clientVersion returns the current client version.
            Web3ClientVersion clientVersion = web3.web3ClientVersion().send();

            // eth_blockNumber returns the number of most recent block.
            EthBlockNumber blockNumber = web3.ethBlockNumber().send();

            // eth_gasPrice, returns the current price per gas in wei.
            EthGasPrice gasPrice = web3.ethGasPrice().send();

            // Print result
            System.out.println("Client version: " + clientVersion.getWeb3ClientVersion());
            System.out.println("Block number: " + blockNumber.getBlockNumber());
            System.out.println("Gas price: " + gasPrice.getGasPrice());
        } catch (IOException ex) {
            throw new RuntimeException("Error whilst sending json-rpc requests", ex);
        }
    }
}

Ganache

Ganache為可以本地啟動的開發區塊鏈服務器
ganache官網地址

執行結果

Successfuly connected to Ethereum
Client version: EthereumJS TestRPC/v2.13.1/ethereum-js
Block number: 0
Gas price: 20000000000

代碼解釋

Web3j web3 = Web3j.build(new HttpService(“HTTP://127.0.0.1:7545”))
連接區塊鏈服務器

Web3ClientVersion clientVersion = web3.web3ClientVersion().send();
客戶端版本號

EthBlockNumber blockNumber = web3.ethBlockNumber().send();
獲取當前區塊鏈中塊個數

EthGasPrice gasPrice = web3.ethGasPrice().send();
獲取gas值