CryptoCoinsInfoClub.com

Ethereum Java Tutorial

Interfacing With Ethereum Smart Contracts Injava

Interfacing With Ethereum Smart Contracts Injava

Interfacing with Ethereum Smart Contracts inJava Since quite a lot of business applications are written in Java, or make use of the JVM for that matter, I believe a primer on how to interface with an Ethereum Smart Contract in Java will prove helpful to the reader. This post requires knowledge of what a Smart Contract is and how to deploy one. To learn why we will probably use a library for interfacing with the Smart Contract a basic understanding of the usage of JSON-RPC in Ethereum is necessary. Lets unveil the supposed magic behind what almost all Ethereum libraries do to interact with the blockchain. Suppose we need to know the gasLimit (maximum amount of computational effort the transactions in a block are allowed to have) of the latest block. Using curl and piping its result to a JSON parser such as jq would, considering we run an Ethereum node on localhost port 8545, look as follows curl --silent -X POST -H "Content-Type: application/json"\ --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}' localhost:8545 | jq .result.gasLimit The above will yield 0x4c4b3c, which is hex-encoded . Since we probably want to read it as a decimal we can add another pipe and the final command becomes curl --silent -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}' localhost:8545\ Leading to the readable result of 4999996. These steps involved are a good showcase on why to introduce an abstraction. Almost all libraries will provide convenient interfaces for these RPC calls. Using the library web3j the command above will translate to web3j.ethGetBlockByNumber(DefaultBlockParameter.valueOf("latest"), Still a lot of steps, and from a software-engineering perspecti Continue reading >>

Interacting With Ethereum Smart Contracts From Android

Interacting With Ethereum Smart Contracts From Android

Interacting with Ethereum Smart Contracts from Android August 23, 2017 by Ondrej Bendo in Android | 6 Comments Usually when you want to interact with smart contracts you need to download the whole ethereum blockchain and keep your local node synchronized. As of writing the blockchain takes up more than 80GB of space on my computer. This might make sense on a desktop computer but is less reasonable on a mobile device. One way to go around this limitation is to use a service like Infura . Infura allows you to connect to a remote ethereum node and execute transactions without having to worry about maintaining and synchronizing your local node. To be able to transact with the smart contract from native Java code I used a library called Web3j . Web3j provides you with utilities for generating smart contract java wrappers and a complete implementation of Ethereums JSON-RPC client API over HTTP and IPC. It provides more features but these were the important ones for this Android Ethereum hello world example. The example smart contract I want to interact with is a Greeter. It stores a greeting message on the blockchainwhich can be read or updated.It looks like this: contract greeter is mortal { /* define variable greeting of the type string */ string greeting; /* this runs when the contract is executed */ function greeter(string _greeting) public { greeting = _greeting; } /* change greeting */ function changeGreeting(string _greeting) public { greeting = _greeting; } /* main function */ function greet() constant returns (string) { return greeting; }} Continue reading >>

Github - Web3j/web3j: Lightweight Java And Android Library For Integration With Ethereum Clients

Github - Web3j/web3j: Lightweight Java And Android Library For Integration With Ethereum Clients

Commercial support and training is available from blk.io . A web3j sample project is available thatdemonstrates a number of core features of Ethereum with web3j, including: Connecting to a node on the Ethereum network Sending Ether from one address to another Deploying a smart contract to the network Reading a value from the deployed smart contract Updating a value in the deployed smart contract Viewing an event logged by the smart contract Add the relevant dependency to your project: org.web3j core 3.4.0 org.web3j core 3.3.1-android Or use Infura , which provides free clients running in the cloud: Web3j web3 = Web3j.build(new HttpService("For further information refer to Using Infura with web3j Instructions on obtaining Ether to transact on the network can be found in the testnet section of the docs . Web3j web3 = Web3j.build(new HttpService()); // defaults to web3ClientVersion = web3.web3ClientVersion().send();String clientVersion = web3ClientVersion.getWeb3ClientVersion(); To send asynchronous requests using a CompletableFuture (Future on Android): Web3j web3 = Web3j.build(new HttpService()); // defaults to web3ClientVersion = web3.web3ClientVersion().sendAsync().get();String clientVersion = web3ClientVersion.getWeb3ClientVersion(); Web3j web3 = Web3j.build(new HttpService()); // defaults to -> { String clientVersion = x.getWeb3ClientVersion(); ...}); Web3j web3 = Web3jFactory.build(new HttpService()); // defaults to web3j also supports fast inter-process communication (IPC) via file sockets to clients running onthe same host as web3j. To connect simply use the relevant IpcService implementation instead ofHttpService when you create your se Continue reading >>

Create A Hello World Contract In Ethereum

Create A Hello World Contract In Ethereum

Building a smart contract using the command line This page will help you build a Hello, World contract on the ethereum command line. If you don't know how to use the command line we recommend you skip this tutorial and instead build a Custom token using the graphical user interface . Smart contracts are account holding objects on the ethereum blockchain. They contain code functions and can interact with other contracts, make decisions, store data, and send ether to others. Contracts are defined by their creators, but their execution, and by extension the services they offer, is provided by the ethereum network itself. They will exist and be executable as long as the whole network exists, and will only disappear if they were programmed to self destruct. What can you do with contracts? Well, you can do almost anything really, but for our getting started guide let's do some simple things: To start you will create a classic "Hello World" contract, then you can build your own crypto token to send to whomever you like. Once you've mastered that then you will raise funds through a crowdfunding that, if successful, will supply a radically transparent and democratic organization that will only obey its own citizens, will never swerve away from its constitution and cannot be censored or shut down. And all that in less than 300 lines of code. Before you begin: Install the Ethereum CLI Learn more about contracts Please confirm that the GUI is closed before entering the geth console.Run geth to begin the sync process (this may take a while on the first run). Now that youve mastered the basics of Ethereum, lets move into your first serious contract. The Frontier is a big open territory and sometimes you might feel lonely, so our first order of business will be to create a little aut Continue reading >>

Spring Boot And Web3j: Easy Microservices For The Ethereum Blockchain

Spring Boot And Web3j: Easy Microservices For The Ethereum Blockchain

Spring Boot and web3j: Easy microservices for the Ethereum Blockchain web3j is a lightweight Java library for integrating with clients on the Ethereum blockchain. And now you can integrate it into your Spring Boot applications. In this article, JAX London speaker Conor Svensson shows how easily web3j integrates with the Spring Framework. web3j now seamlessly integrates with the Spring Framework , thanks to the web3j Spring Boot Starter . Using Spring Boot , its trivial to create production-ready services using web3j to work with the Ethereum blockchain. Start by creating a new Spring Boot application . Then add theweb3j-spring-boot-starterto your Gradle or Maven configuration: dependencies { compile 'org.web3j:web3j-spring-boot-starter:1.0.0' ...} Now create a service using web3j, and Spring will create and configure the web3j instance for you! @Servicepublic class Web3jSampleService { @Autowired private Web3j web3j; public String getClientVersion() throws IOException { Web3ClientVersion web3ClientVersion = web3j.web3ClientVersion().send(); return web3ClientVersion.getWeb3ClientVersion(); }} The default HTTP endpoint of your Ethereum client is used (however, you can easily change this in your application properties file. # An infura endpointweb3j.client-address = token id> # Or, an IPC endpoingweb3j.client-address = /path/to/file.ipc Code for this example is available here . For further information on check out the web3j project home page and the spring-boot-starter project . The article was originally published on Conor Svenssons blog . Conor Svenssonwill be delivering a talk at JAX London thatwill explore using Ethereum to build Java applications on the blockchain. In his talk, Conor will be demystifying this technology and demonstrating how you can integrate JVM app Continue reading >>

How To Send Ethereum Transactions With Java

How To Send Ethereum Transactions With Java

How to Send Ethereum Transactions With Java How to Send Ethereum Transactions With Java If you're Java developer dipping into the Ethereum blockchain, here's what you need to know about the ins and outs of sending transactions. Aug. 11, 17 Java Zone Build vs Buy a Data Quality Solution: Which is Best for You? Gain insights on a hybrid approach. Download white paper now! After Ive expressed my concerns about the blockchain technology , lets get a bit more practical with the blockchain. In particular, with Ethereum. I needed to send a transaction with Java, so I looked at EthereumJ . You have three options: Full node you enable syncing, which means the whole blockchain gets downloaded. It takes a lot of time, so I abandoned that approach Light node you disable syncing, so you just become part of the network, but dont fetch any parts of the chain. Not entirely sure, but I think this corresponds to the light mode of geth (the Ethereum CLI). You are able to send messages (e.g. transaction messages) to other peers to process and store on the blockchain, but you yourself do not have the blockchain. Offline (no node) just create and sign the transaction, compute its raw representation (in the Ethereum RLP format) and push it to the blockchain via a centralized API, e.g. the etherscan.io API . Etherscan is itself a node on the network and it can perform all of the operations (so it serves as a proxy) Before going further, maybe its worth pointing out a few general properties of the blockchain (the Ethereum one and popular cryptocurrencies at least) it is a distributed database, relying on a peer-to-peer (overlay) network, formed by whoever has a client software running (wallet or otherwise). Transactions are in the form of I (private key owner) want to send this amount to that Continue reading >>

Full Stack Hello World Voting Ethereum Dapp Tutorialpart1

Full Stack Hello World Voting Ethereum Dapp Tutorialpart1

Techie, Foodie, Traveler, Tinkering with Blockchain at www.zastrin.com Full Stack Hello World Voting Ethereum Dapp Tutorial Part1 In my previous post , I explained the high level architecture of Ethereum platform comparing it to a web application. As a developer, the best way to learn any new technology is by diving in and building toy applications. In this post, lets build a simple Hello World! application which is a Voting application. The application is extremely simple, all it does is initialize a set of contestants, let anyone vote for the candidates and display the total votes received by each candidate. The goal is not to just code an application but to learn the process of compiling, deploying and interacting with it. I have deliberately avoided using any dapp frameworks to build this application because the frameworks abstract away lot of the details and you fail to understand the internals of the system. Also, when you do use a framework, you will have more appreciation for all the heavy lifting the framework does for you! In lot of ways, this article is a continuation of the previous post . If you are new to the world of Ethereum, I recommend reading it before continuing. Learn the process of writing a contract, compiling it and deploying it in your development environment. Interact with the contract on the blockchain through a nodejs console. Interact with the contract through a simple web page to display the vote counts and vote for candidates through the page. The entire application set up and build was done on a fresh installation of ubuntu 16.04 xenial. I have set up and tested the application on macos as well. This is how I would visualize this application we are going to build. 1. Setting up the development environment Instead of developing the app ag Continue reading >>

Introduction To Ethereumj

Introduction To Ethereumj

If you're new here, you may want to check out the "API Discoverability with Spring and Spring HATEOAS" live Webinar . Thanks for visiting! I just announced the new Spring 5 modules in REST With Spring: In this article, we take a look at the EthereumJ library that allows us to interact with the Ethereum blockchain, using Java. First, lets just briefly dive into what this technology is all about. Ethereum is acryptocurrencyleveraging a distributed, peer-to-peer, database in the form of a programmableblockchain, the Ethereum Virtual Machine (EVM). Its synchronized and operated through disparate but connectednodes. As of 2017, Nodessynchronize theblockchainthrough consensus, create coins through mining (proof of work), verify transactions, executesmart contracts written in Solidity , and run the EVM. The blockchainis divided intoblockswhich containaccount states(including transactions betweenaccounts) andproof of work. The org.ethereum.facade.Ethereumclass abstracts and unites many packages of EthereumJ into one easy to use interface. Its possible to connect to a node to sync with the overall network and, once connected, we can work with the blockchain. Ethereum ethereum = EthereumFactory.createEthereum(); To connect to the network, we must first connect to a node, i.e.a server running the official client. Nodesare represented by theorg.ethereum.net.rlpx.Node class. The org.ethereum.listener.EthereumListenerAdapter handles blockchain events detected by our client after connection to a nodehas been established successfully. Lets connect to a node on the network. This can be done manually: String ip = "port = 8345;String nodeId = "a4de274d3a159e10c2c9a68c326511236381b84c9ec...";ethereum.connect(ip, port, nodeId); Connecting to the network can also be done automatically using Continue reading >>

Ethereum In Practice - Quick Start Guide

Ethereum In Practice - Quick Start Guide

Ive found Ethereum documentation to be very thorough. And yet,Ive found it hard to understand how to approach Ethereum in practice - connect to the network, developand debug of a contract, deploy it and actually use it. This is what this post / guide / tutorial, and few coming posts, are about.Straight and to the point. This post certainly doesnt cover the theory which is already well explained in the official documentation, butrather focuses on how to get one up and running in, really, few minutes; because it is really that simple when you know how. And also when you know some theory as well. So, if you didnt read the official documentation, please, do so. Thispost assumes that at the very least one knows what Ethereum is and how it works and what an account, an EOA, a contract, gas and transactions are ,and finally would like to put it all to practice. There is a bare minimum of basic theory below otherwise. Here, in this post, following subject are covered: Run a private network, create a contract and deploy it to Homestad Ethereum network is decentralized. It means that there is no central server and what is called ethereumclient (like eth or geth for example) is really a part of the network when it is online. The network is allclients altogether. You know BitTorrent, right? So this is kind of the same, but better. So, step #1 - install the client. Again, there is no single client, there are multiple to chose from. Ethereum isdescribed in a specification, and multiple clients exist all implementing it. But really, as of the time of thiswriting, the most popular is geth, which is my choice as well, and which is the one used throughout this post in theexamples. Install instructions depend on the OS, so Im just pointing to geth GitHub repository . If you see the geth Continue reading >>

Can I Write And Deploy Smart Contracts In Java Language?

Can I Write And Deploy Smart Contracts In Java Language?

Can I write and deploy smart contracts in Java language? I am a Java developer. I want to write a smart contract using Java and deploy it to a private blockchain network. Does Ethereum provide the facility to write smart contracts using Java language? If yes, how can I do this? May you can any help from here : github.com/ethereum/ethereumj A.K. Aug 10 '16 at 13:00 Check out tendermint for smart contracts in any language: github.com/tendermint/tendermint . Here's an example application in Java: github.com/wolfposd/TMChat Ethan Nov 7 '16 at 21:40 Currently, Smart Contracts can be written in three languages: LLL(Lisp Like Language) - Similar to Assembly You can find more information about these languages here . Solidity is designed especially for writing smart contracts and is the flagship language of Ethereum. You can start reading about it here . You can not write contracts in Java, but deploying should work with the Ethereum Contract API native in Java. The goal is to ease the integration of Ethereum in a Java project. Easy configuration of the network and keypair use Have type safety in regards of input and output values Easy synchronization when creating a transaction Transaction creation returns Future, simple calls returns the value itself It's not out yet but you might be interested in Corda, which is being developed by Mike Hearn and his team on behalf of the R3 consortium. This targets Java developers, and doesn't use a blockchain, as is appropriate for a lot of private blockchain projects in the financial sector. Per this discussion some code will be released soon: To start you can use web3j . It is Java library that allow the iteration of java application with contracts in the Ethereum network. It doesn't provide the capability to write contracts in java, but Continue reading >>

Getting Started Web3j 3.3.1 Documentation

Getting Started Web3j 3.3.1 Documentation

Web3j web3 = Web3j.build(new HttpService()); // defaults to web3ClientVersion = web3.web3ClientVersion().send();String clientVersion = web3ClientVersion.getWeb3ClientVersion(); To send asynchronous requests using a CompletableFuture (Future on Android): Web3j web3 = Web3j.build(new HttpService()); // defaults to web3ClientVersion = web3.web3ClientVersion().sendAsync().get();String clientVersion = web3ClientVersion.getWeb3ClientVersion(); Web3j web3 = Web3j.build(new HttpService()); // defaults to -> { String clientVersion = x.getWeb3ClientVersion(); ...}); Web3j web3 = Web3jFactory.build(new HttpService()); // defaults to web3j also supports fast inter-process communication (IPC) via file sockets to clients running onthe same host as web3j. To connect simply use the relevant IpcService implementation instead ofHttpService when you create your service: // OS X/Linux/Unix:Web3j web3 = Web3j.build(new UnixIpcService("/path/to/socketfile"));...// WindowsWeb3j web3 = Web3j.build(new WindowsIpcService("/path/to/namedpipefile"));... Note: IPC is not available on web3j-android. Working with smart contracts with Java smart contract wrappers web3j can auto-generate smart contract wrapper code to deploy and interact with smart contractswithout leaving the JVM. To generate the wrapper code, compile your smart contract: $ solc .sol --bin --abi --optimize -o / Then generate the wrapper code using web3js Command Line Tools : web3j solidity generate /path/to/.bin /path/to/.abi -o /path/to/src/main/java -p com.your.organisation.name Now you can create and deploy your smart contract: Web3j web3 = Web3j.build(new HttpService()); // defaults to credentials = WalletUtils.loadCredentials("password", "/path/to/walletfile");YourSmartContra Continue reading >>

How To Learn Solidity: The Ultimate Ethereum Coding Guide

How To Learn Solidity: The Ultimate Ethereum Coding Guide

How To Learn Solidity: The Ultimate Ethereum Coding Guide Angel Investors, Startups & Blockchain developers... This Guide will walk you step -by-step in learning Solidity. The Ethereum Foundation has been shaking up the world of blockchain since the early days of the project, around late 2013 and early 2014. Ethereum really kickstarted the Bitcoin 2.0 and what we think of as the blockchain movement, after the first big Bitcoin bubble up past $1000 USD on the markets got everyones attention. Ethereum is a blockchain project with a cryptocurrency, Ether, similar to Bitcoin, but Ethereum has the added feature of a (nearly) Turing- complete virtual machine language and processing capability embedded into the node implementation. The Ethereum Virtual Machine (EVM) allows Ethereum nodes to actually store and process data in exchange for payment, responding to real-world events and allowing a lot of new opportunities to support on-chain applications that were never before available to developers and real-world users. I had the luck to actually be in Switzerland in early 2014, and to get to visit an Ethereum holon and hang out with some of the Ethereum founders before the Ether token sale, back when they were self-funded. I asked Mihai Alisie what an Ethereum smart contract is, and he explained: Smart-contracts are a way for people all across the globe to do business with each other even if they dont speak the same language or use the same currency. So thats really the perspective I begin with, the idea that we can define programmatically the rules of a business contract, in a simple machine language, to bring people together and allow them to conduct business in a trustable, secure, and automated fashion. Solidity Language itself is a tool that we use to generate machine-leve Continue reading >>

Ethereum Development Tutorial

Ethereum Development Tutorial

The purpose of this page is to serve as an introduction to the basics of Ethereum that you will need to understand from a development standpoint, in order to produce contracts and decentralized applications. For a general introduction to Ethereum, see the white paper , and for a full technical spec see the yellow papers, although those are not prerequisites for this page; that is to say, this page is meant as an alternative introduction to Ethereum specifically targeted towards application developers. Ethereum is a platform that is intended to allow people to easily write decentralized applications (apps) using blockchain technology. A decentralized application is an application which serves some specific purpose to its users, but which has the important property that the application itself does not depend on any specific party existing. Rather than serving as a front-end for selling or providing a specific party's services, a app is a tool for people and organizations on different sides of an interaction used to come together without any centralized intermediary. Even necessary "intermediary" functions that are typically the domain of centralized providers, such as filtering, identity management, escrow and dispute resolution, are either handled directly by the network or left open for anyone to participate, using tools like internal token systems and reputation systems to ensure that users get access to high-quality services. Early examples of apps include BitTorrent for file sharing and Bitcoin for currency. Ethereum takes the primary developments used by BitTorrent and Bitcoin, the peer to peer network and the blockchain, and generalizes them in order to allow developers to use these technologies for any purpose. The Ethereum blockchain can be alternately described Continue reading >>

How To Send Ethereum Transactions With Java

How To Send Ethereum Transactions With Java

After Ive expressed my concerns about the blockchain technology , lets get a bit more practical with the blockchain. In particular, with Ethereum. I needed to send a transaction with Java, so I looked at EthereumJ . You have three options: Full node you enable syncing, which means the whole blockchain gets downloaded. It takes a lot of time, so I abandoned that approach Light node you disable syncing, so you just become part of the network, but dont fetch any parts of the chain. Not entirely sure, but I think this corresponds to the light mode of geth (the ethereum CLI). You are able to send messages (e.g. transaction messages) to other peers to process and store on the blockchain, but you yourself do not have the blockchain. Offline (no node) just create and sign the transaction, compute its raw representation (in the ethereum RLP format) and push it to the blockchain via a centralized API, e.g. the etherscan.io API . Etherscan is itself a node on the network and it can perform all of the operations (so it serves as a proxy) Before going further, maybe its worth pointing out a few general properties of the blockchain (the ethereum one and popular cryptocurrencies at least) it is a distributed database, relying on a peer-to-peer (overlay) network, formed by whoever has a client software running (wallet or otherwise). Transactions are in the form of I (private key owner) want to send this amount to that address. Transactions can have additional data stored inside them, e.g. representing what they are about. Transactions then get verified by peers (currently using a Proof-of-work based consensus) and get stored on the blockchain, which means every connected peer gets the newly created blocks (each block consisting of multiple transactions). Thats the blockchain in short, Continue reading >>

Segundo Tutorial: Programando Ethereum Com Java

Segundo Tutorial: Programando Ethereum Com Java

Segundo Tutorial: Programando Ethereum com Java Agora que j vimos uma operao simples de envio e recebimento de valores entre contas / wallets no Ethereum, vamos entrar no mundo dos contratos inteligentes. Um contrato inteligente um software cujo deploy feito na rede Ethereum, ou seja, distribuido emtodos os ns da rede. Para este exemplo vamos utilizar a linguagem Solidity para criao do contrato, voc tambm pode utilizar a linguagem Serpent . Vamos criar um contrato bem simples, que j est no repositrio do GitHub: parity chain kovanrpcapi eth,net,web3,personal,parity O Smart Contract de exemplo est dentro do projeto Maven. A seguir listo em 10 passos, a criao, compilao e chamada do Smart Contract em Java. O Solc o solidity comand line compiler, com ele que iremos compilar nossos smart contracts, gerando ento os arquivos .abi e .bin. O arquivo .abi (application binary interface specification) a especificao do Smart Contract, por meio desta especificao que outros contratos sabero quais mtodos esto disponveis. um arquivo no formato JSON. O arquivo .bin o contrato compilado contento hex-encoded binarizado. sudo add-apt-repository ppa:ethereum/ethereumsudo apt-get update Neste link voc pode baixar a verso para windows: $ unzip web3j-.zip creating: web3j-1.0.2/lib/ inflating: web3j-1.0.2/lib/core-1.0.2-all.jar creating: web3j-1.0.2/bin/ inflating: web3j-1.0.2/bin/web3j inflating: web3j-1.0.2/bin/web3j.bat$ ./web3j-/bin/web3j Dentro do diretrio DIRETORIO_WEB3J\bin voc encontrar o executvel web3j (linux), ou o arquivo em lotes (web3j.bat para windows). Sendo DIRETORIO_WEB3J o local onde voc descompactou o arquivo do web3j. solc ./CAMINHO/ContratoAlex.sol bin abi overwrite optimize -o /CAMINHO_RESOURCES/ Onde /CAMINHO_RESOURCES o caminho dentro do seu projeto Maven onde ficam os r Continue reading >>

More in ethereum