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Ethereum Java Application

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 >>

Integrating The Ethereum Blockchain Into Java Apps

Integrating The Ethereum Blockchain Into Java Apps

Integrating the Ethereum Blockchain into Java Apps How to access a distributed ledger technology blockchain from a Java application using web3j. The Ethereum blockchain is a decentralized platform that is the backbone of a secure, decentralized internet and is driven by the eponymous cryptocurrency Ether. Conor Svensson authored web3j, a lightweight Java library for building Java applications on the Ethereum blockchain. In a first article , which appeared in the Java Magazine, Conor Svensson gives the background of the Ethereum blockchain technology and explains how to create a blockchain that is connected to a Java application. Web3j, a wrapper of client remote procedure calls using JSON, manages the transaction interactions with Ethereum clients. In a second article , he details how to use web3j to query the Ethereum blockchain via its reactive-functional API. He explains how to use RxJavas Observables to add reactive functionality to theblockchain. An Ethereum client like Geth or Parity is the first step to getting you started. Clients will synchronize the Ethereum blockchain with one another and provide a gateway to interact with the blockchain. Ethereum takes care of Ether cryptocurrency payment transactions via the network. With just a few lines of code, you can hook up to the Ethereum blockchain and be notified of new blocks being added to the blockchain and start pulling information out of the blockchain in real time. For code and step by step examples, read the full article here for more information, please visit: web3j project and Conor's blog 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 >>

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 >>

Java And The Blockchain - Building Java Applications On Ethereum With Web3j 3.0

Java And The Blockchain - Building Java Applications On Ethereum With Web3j 3.0

Java and the Blockchain - building Java applications on Ethereum with web3j 3.0 **Important notice** YOU MUST ALSO REGISTER ON THE SKILLS MATTER SITE >>In this talk Conor Svensson will provide an overview of what blockchain/distributed ledger technology is, and how the Ethereum blockchain works. We'll discuss smart contracts, and demonstrate how you can deploy and interact with smart contracts on Ethereum, all from within the JVM, thanks to the open-source library web3j, which has just had its milestone 3.0 release! We will also learn about web3j's usage of ReactiveX's Observable, and the great enhancements it was able to bring to web3j, both internally and externally for its users working with the blockchain. Conor Svensson is the author of web3j, the JVM library for integrating with the Ethereum blockchain. He is also the founder of blk.io ( ) [7] who provide the foundations for enterprises wishing to work with blockchain technology. Continue reading >>

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 >>

Github - Ethereum/ethereumj: Java Implementation Of The Ethereum Yellowpaper. For Json-rpc And Other Client Features Check Ethereum Harmony

Github - Ethereum/ethereumj: Java Implementation Of The Ethereum Yellowpaper. For Json-rpc And Other Client Features Check Ethereum Harmony

Java implementation of the Ethereum yellowpaper. For JSON-RPC and other client features check Ethereum Harmony If nothing happens, download GitHub Desktop and try again. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. EthereumJ is a pure-Java implementation of the Ethereum protocol. For high-level information about Ethereum and its goals, visit ethereum.org . The ethereum white paper provides a complete conceptual overview, and the yellow paper provides a formal definition of the protocol. We keep EthereumJ as thin as possible. For JSON-RPC support and other client features check Ethereum Harmony . Adding as a dependency to your Maven project: org.ethereum ethereumj-core 1.6.3-RELEASE repositories { mavenCentral() jcenter() maven { url "} } compile "org.ethereum:ethereumj-core:1.6.+" As a starting point for your own project take a look at git clone ethereumjcp ethereumj-core/src/main/resources/ethereumj.conf ethereumj-core/src/main/resources/user.confvim ethereumj-core/src/main/resources/user.conf # adjust user.conf to your needs./gradlew clean shadowJarjava -jar ethereumj-core/build/libs/ethereumj-core-*-all.jar > git clone cd ethereumj> ./gradlew run [-PmainClass=] ./gradlew run -PmainClass=org.ethereum.samples.BasicSample./gradlew run -PmainClass=org.ethereum.samples.FollowAccount./gradlew run -PmainClass=org.ethereum.samples.PendingStateSample./gradlew run -PmainClass=org.ethereum.samples.PriceFeedSample./gradlew run -PmainClass=org.ethereum.samples.PrivateMinerSample./gradlew run -PmainClass=org.ethereum.samples.TestNetSample./gradlew run -Pmain Continue reading >>

Java And The Blockchain - Building Java Applications On Ethereum With Web3j 3.0

Java And The Blockchain - Building Java Applications On Ethereum With Web3j 3.0

In this talk Conor Svensson will provide an overview of what blockchain/distributed ledger technology is, and how the Ethereum blockchain works. We'll discuss smart contracts, and demonstrate how you can deploy and interact with smart contracts on Ethereum, all from within the JVM, thanks to the open-source library web3j, which has just had its milestone 3.0 release! We will also learn about web3j's usage of ReactiveX's Observable, and the great enhancements it was able to bring to web3j, both internally and externally for its users working with the blockchain. Conor Svensson is the author of web3j, the JVM library for integrating with the Ethereum blockchain. He is also the founder of blk.io [7] who provide the foundations for enterprises wishing to work with blockchain technology. **N.B. Skills Matter are hosting this LJC event and will allocate a meeting room based on the number of registrations they receive via their own link. It is thereforeessential that you confirm your place at this link: 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 >>

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 >>

Business Applications On Blockchains: Eclipse Scout, Ethereum And Web3j

Business Applications On Blockchains: Eclipse Scout, Ethereum And Web3j

Business Applications on Blockchains: Eclipse Scout, Ethereum and web3j 06.01.2017, Matthias Zimmermann, Christoph Langewisch, Philipp Bauer This blog post provides a brief introduction into the blockchain world and shows how to integrate the Ethereum Blockchain with a Java based Business Application. Specifically we describe the implemented "micro"-banking prototype with Eclipse Scout (the business application side), Ethereum (the blockchain) and web3j (a Java library to communicate with Ethereum). Blockchain technologies provide a fully decentralized ledger based on peer-to-peer networks. The Blockchain promise is that network participants can rely on this ledger to safely interact with each other without the need of any central authority or trusting each other. This ledger is represented by a chain of blocks (this is where the term blockchain comes from) where each block contains a number of transactions that have taken place between the network participants. A key feature of blockchain technologies is that blocks in the chain cannot be altered in any way. The only way to change the blockchain is adding new blocks. Bitcoin created in 2009 by Satoshi Nakamoto (an unknown person or group of persons) - represents the first successful implementation of blockchain technology. Today, Bitcoin represents the gold standard of virtual currencies and enjoys growing popularity and its currency is soaring again. Luckily, Bitcoin has also set the precedent for blockchain technology to be open source. Recommended pointers being: The whitepaper , the code and a technical book (written in Asciidoctor) are nice examples. Ethereum was originally conceived by Vitalik Buterin and in late 2013 he described its concepts in a whitepaper . The goal of Ethereum is to provide a blockchain pla 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 >>

What Is Ethereum? A Step-by-step Beginners Guide

What Is Ethereum? A Step-by-step Beginners Guide

If you want to know what is Ethereum and how it works and what it can be used for, without going deep into the technical abyss, this guide is perfect for you. Important Note: This guide assumes a basic understanding of blockchain technology. If youre unfamiliar with blockchain, check out this step by step introduction for beginners . Beyond Bitcoin & first generation decentralized applications Although commonly associated with Bitcoin , blockchain technology has many other applications that go way beyond digital currencies. In fact, Bitcoin is only one of several hundred applications that use blockchain technology today. [Blockchain] is to Bitcoin, what the internet is to email. A big electronic system, on top of which you can build applications. Currency is just one. Sally Davies, FT Technology Reporter Until relatively recently, building blockchain applications has required a complex background in coding, cryptography, mathematics as well as significant resources. But times have changed. Previously unimagined applications, from electronic voting & digitally recorded property assets to regulatory compliance & trading are now actively being developed and deployed faster than ever before. By providing developers with the tools to build decentralized applications, Ethereum is making all of this possible. At its simplest, Ethereum is an open software platform based on blockchain technology that enables developers to build and deploy decentralized applications. Is Ethereum similar to Bitcoin? Well, sort of, but not really. Like Bitcoin , Ethereum is a distributed public blockchain network. Although there are some significant technical differences between the two, the most important distinction to note is that Bitcoin and Ethereum differ substantially in purpose and capabil Continue reading >>

Ethereum - Interacting A Smart Contract From Java Application - Stack Overflow

Ethereum - Interacting A Smart Contract From Java Application - Stack Overflow

Interacting a smart contract from Java application I am working on interacting my smart contract from java application, I am using testrpc. To interact with the smart contract we need : 1- connect to the local host 2- have an account to send transactions (credentials). 3- deploy the contract and get the address (deployed to testrpc network using truffle and already have the address) 1- Web3j web3 = Web3j.build(new HttpService()); // defaults to Credentials credentials = WalletUtils.loadCredentials("password", "/path/to/walletfile");3- YourSmartContract contract = YourSmartContract.deploy( , , GAS_PRICE, GAS_LIMIT, , , ..., ).get(); // constructor params My questions are: how I can use testrpc accounts for "credentials"??!! How I can use the address of the smart contract which already deployed by truffle?? how I can use testrpc accounts for "credentials"??!! You need the private and public keys to create the Credentials object. TestRPC displays the private keys when you start. They change on each restart, so if you want to keep them static, you can specify the initial set of accounts using your own private keys with the --accounts option. Format: testrpc --account "," testrpc --account "0x70f1384b24df3d2cdaca7974552ec28f055812ca5e4da7a0ccd0ac0f8a4a9b00,300000000000000000000" --account "0xad0352cfc09aa0128db4e135fcea276523c400163dcc762a11ecba29d5f0a34a,300000000000000000000" With the private key, you can generate the public key. There are several examples online of how to do this. See here for a JS example or here for an example using web3j (this creates a new key pair, but you should be able to reuse it). With the public and private keys, you can now create the Credentials object: import org.web3j.crypto.Cr Continue reading >>

Building Java Applications On Ethereum By Conor Svensson

Building Java Applications On Ethereum By Conor Svensson

Building Java Applications on Ethereum by Conor Svensson In this talk, Conor Svensson will provide an overview of what blockchain/distributed ledger technology is, and how the Ethereum blockchain works. We'll discuss smart contracts, and demonstrate how you can deploy and interact with smart contracts on Ethereum, all from within the JVM, thanks to the open-source library web3j ( ), which has just had its milestone 3.0 release! We will also learn about web3j's usage of ReactiveX's Observable, and the great enhancements it was able to bring to web3j, both internally and externally for its users working with the blockchain. 19:15 Refreshments (Pizza, Beer/wine) and Networking Conor Svensson is the author of web3j, the JVM library for integrating with the Ethereum blockchain. He is also the founder of blk.io ( ) who provides the foundations for enterprises wishing to work with blockchain technology. Follow Conor on twitter: Fintek.io. Creating beautiful, maintainable and scalable web applications for the fintech industry. Passionate about code quality and new technologies. This event is co-hosted with DevChain Meetup: You can also book this event on Eventbrite ( ) with Progscon Conference. ( www.progscon.co.uk ) Follow us on twitter: Continue reading >>

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