web3j Sample Project

This project provides a very simple starter application for working with web3j and the testEthereum network (testnet) known as Rinkeby.

The demo deploys a hello world smart contract which contains a greeting message. The currentgreeting message can be read and modified in the smart contract.

In order to run this demo, three pieces of information are required:

1. Ethereum client (or node) endpoint. The simplest thing to do isrequest a free access token from Infura.
2. A wallet file. This can be generated using the Epirus CLI.
3. Some Ether. This can be requested from the Rinkeby Faucet.

Once these details have been added to the main Application class, you'll be good to go.

Functionality

This application demonstrates a number of core features of web3j and Ethereum:

• Connecting to a node on the Ethereum network
• Loading an Ethereum wallet file
• 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

Background

This application has purposefully been kept as simple as possible with the aim of demonstratinghow to deploy and work with a smart contract on the decentralised Ethereum network.

If you require further background information about the above configuration items for the projectyou can refer to the below.

For a more comprehensive overview, I recommend you read theJava Magazine Article, watchtheYouTube talk, and read all of thedocumentation.

Smart contracts

The contained smart contract is based on theGreeter contract example, with the addition that the valuestored in the Greeter can be modified.

The associated Java smart contract wrapper is named Greeter.

For more background on smart contracts, refer to thesmart contracts section of the docs.

Infura

If you don't want to sign up to Infura, and would like to run a node yourself, there areinstructions in the getting startedsection of the docs.

Testnets

For more information on the different Ethereum test networks (or testnets), referto thetestnet overview in the docs.

Ether

For background on Ether, refer to the transactionsoverview section of the docs.

Wallets and transaction signing

For a more technical overview of working with wallet files, refer to theOffline transaction signingsection of the docs.

Viewing requests

A logback configuration is included in the project dependencies allowing the logging of protocolmessages if required. To enable, simply change the following line in the logback configurationto read:

<logger name="org.web3j.protocol" level="DEBUG"/>