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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 >>

Create Ethereum Account Using Web3j And Java

Create Ethereum Account Using Web3j And Java

Create Ethereum Account Using Web3j And Java Posted by Sudhakar Pandey | Last Updated: 14-Nov-17 Following are the simple steps are need to be done for creating new account using web3j and java. 1- Add maven dependency of Web3j in pom.xml as 2- Create web3j object and connect to ethereum server with its ip and port Web3j web3 = Web3j.build(new HttpService("ip with port")); 3- Execute wallet utils function for generating wallet file on ethereum keystore path. String walletFileName = WalletUtils.generateFullNewWalletFile(password,new File("Keystore path")); Above function needs to be two parameter password and wallet file location which should be the keystore location of ethereum server. 4- The above function returns new created wallet file name. This file name include newly generated wallet address in its name string. ex- Wallet file name looks like- "UTC--2017-07-13T10-23-04.815000000Z--95839e87e764057a628b7cd1d223861b2695712c.json". for extracting wallet address we can follow one of the approach as below String[] fetchAddress=walletFileName.split("--");String getAddress = fetchAddress[fetchAddress.length-1].split("\\.")[0]; 5- After that we can store this information on database for future references. createNewWallet(Long userId) { LOGGER.info("Enter into createNewWallet service"); Map (); try { LOGGER.info("Enter before connect geth"); Web3j web3 = Web3j.build(new HttpService(envConfiguration.getTestnetServerIp())); LOGGER.info("after check connection with geth"); String password = PasswordEnoderDecoder.generatePhassprase(); LOGGER.info("Connect with ethereum ---" + "-- password using for create wallet is " + password); UserWallet userWallet = new UserWallet(); String walletFileName = WalletUtils.generateFullNewWalletFile(password, new File(envConfiguration.getTestne 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 >>

Introduction To Ethereum Smart Contract Clients (web3js Library)

Introduction To Ethereum Smart Contract Clients (web3js Library)

Introduction to Ethereum Smart Contract Clients (Web3js Library) After some discussions around solidity smart contract design and issues in the last two articles ( Here and Here ), we will take a look at how we can integrate smart contracts with enterprise clients applications. There are multiple technologies that can interact with an ethereum node ( ethereum blockchain client ). The basic architecture of the EVM ( ethereum virtual machine ) that runs smart contracts is that all calls to the contract are executed as a transaction where the ether required for a contract method executed is transferred from the calling account address to the contract account address. The contract code resides on the contract address on the blockchain and expects the calls to come in as transactions carrying the method parameter data along with the transaction as input. To enable a standard format for all clients, the method name, and parameters need to be marshaled in a recommended format. Ethereum standard clients expose an interface for making the RPC (Remote Procedure Call) to contract code deployed on the blockchain. This is called the RPC interface serving as an HTTP post requests at default port of 8545 for the go, c++ and parity client. This can usually be customized as a command parameter or a configuration file property: --rpc --rpcaddr --rpcport The RPC format structured on the popular JSON-RPC format. The format is complex especially for marshaling parameter values based on the types. The recommended encoding scheme has to be followed as defined with the correct padding to ensure the EVM is able to decode them. Due to the low-level complexity of the JSON_RPC format, there are a number of wrapper libraries available that simplify the call format. The oldest one is a JavaScr Continue reading >>

Verwendung Von Ethereum Smart Contracts Injava

Verwendung Von Ethereum Smart Contracts Injava

Verwendung von Ethereum Smart Contracts inJava Etliche Geschftsanwendungen sind in Java geschrieben bzw. laufen auf der JVM . Folglich sind wir der Meinung, dass die Grundlagen wie ein Ethereum Smart Contract in eine bestehende Anwendung eingebunden wird, sich fr den Leser als hilfreich erweist. Der vorliegende Artikel setzt das Wissen was ein Smart Contract ist, und wie er verteilt wird, voraus. Um zu verstehen, warum wir eine library verwenden, um mit dem Smart Contract zu interagieren, ist es hilfreich ein Verstndnis zu haben wie JSON-RPC in Ethereum eingesetzt wird. Hinter der Funktionalitt, die eine Library vermeintlich verbirgt, steckt wenig Magie. Angenommen wir mchten den Wert von gaslimit, dem aktuellen Maximum an rechnerischem Aufwand, welcher in einem Block geleistet werden kann, herausfinden. Mit curl und einem JSON parser wie jq knnen wir, unter der Annahme, dass ein Ethereum Knoten auf localhost port 8545 aktiv ist, den folgenden Befehl absetzen 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 Das Ergebnis war zum Aufrufzeitpunkt "0x4c4b3c". Es ist hexadezimal . Um den Wert ohne Nachdenken lesen zu knnen, verwenden wir eine weitere Pipe und der Befehl wird zu 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 | xargs printf '%d\n' welcher uns das Ergebnis 4999996 liefert. All diese Schritte sollen als Beispiel fungieren, warum die Einfhrung einer Abstraktion Sinn macht. Nahezu alle Libraries bieten bequeme Interfaces fr diese RPC calls. Mit der Library web3j wird der lange Aufruf ob 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 >>

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 >>

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 >>

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 >>

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 >>

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 >>

Starting With Ethereum - Writing A Contract

Starting With Ethereum - Writing A Contract

Starting with Ethereum - Writing a contract In the latest post , the required infrastructure to do something on Ethereum was set up. Now is the time to roll up our sleeves and start writing some code on it. In this post, Ill show how to write a trivial contract. A smart contract is a computer protocol intended to facilitate, verify, or enforce the negotiation or performance of a contract. That doesnt tell much. My understanding is that on the blockchain in general, and on Ethereum in particular, smart contracts are just code. Which is a good thing, since we are developers, and writing code is our bread-and-butter (or at least it should be). As Ethereum has an Ethereum Virtual Machine, it can run contracts, code, in the form of dedicated bytecode. However, just like in Java, directly writing such bytecode is not really feasible for non-trivial software. Thus, a high-level language is required. There are several of those available, that compile to EVM bytecode: Ive had not so great experiences with both Python and C The documentation is solid (pun intended) Solidity is a contract-oriented, high-level language for implementing smart contracts. It was influenced by C++, Python and JavaScript and is designed to target the Ethereum Virtual Machine (EVM). Solidity is statically typed, supports inheritance, libraries and complex user-defined types among other features. An IntelliJ plugin : To install the plugin, go to IntelliJ IDEA Preferences Plugins. Then click on the Browse Repositories button, and search for Solidity. After restart, you can select File New Smart contract to create new Solidity .sol files. Last but not least, one can try the online editor, called Remix . Remix can also run the compiled code on a limited set of networks, and offers a debugger, which is a goo Continue reading >>

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