Web3j is a lightweight, highly modular, reactive, type safe Java and Android library for working with Smart Contracts and integrating with clients (nodes) on the Ethereum network:

This allows you to work with the Ethereum blockchain, without the additional overhead of having to write your own integration code for the platform.

The Java and the Blockchain talk provides an overview of blockchain, Ethereum and Web3j.

• Complete implementation of Ethereum's JSON-RPC client API over HTTP and IPC
• Ethereum wallet support
• Auto-generation of Java smart contract wrappers to create, deploy, transact with and call smart contracts from native Java code (Solidity and Truffle definition formats supported)
• Reactive-functional API for working with filters
• Ethereum Name Service (ENS) support
• Support for Parity's Personal, and Geth's Personal client APIs
• Support for Alchemy and Infura, so you don't have to run an Ethereum client yourself
• Comprehensive integration tests demonstrating a number of the above scenarios
• Command line tools
• Android compatible
• Support for JP Morgan's Quorum via web3j-quorum
• Support for EEA Privacy features as described in EEA documentation and implemented in Hyperledger Besu.

It has five runtime dependencies:

• RxJava for its reactive-functional API
• OKHttp for HTTP connections
• Jackson Core for fast JSON serialisation/deserialization
• Bouncy Castle for crypto
• Jnr-unixsocket for *nix IPC (not available on Android)
• Java-WebSocket

It also uses JavaPoet for generating smart contract wrappers.

The simplest way to start your journey with Web3j is to create a project. We provide this functionality using the Web3j CLI. This latter can be installed as follows:

For Unix:

curl -L get.web3j.io | sh && source ~/.web3j/source.sh

For Windows, in Powershell:

Set-ExecutionPolicy Bypass -Scope Process -Force; iex ((New-Object System.Net.WebClient).DownloadString('https://raw.githubusercontent.com/web3j/web3j-installer/master/installer.ps1'))

Create a new project by running:

$ web3j new 

Or use our Maven or Gradle plugins to generate java files from Solidity contracts.

Java:

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>4.10.2</version>
</dependency>

Android:

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>4.8.7-android</version>
</dependency>

Java:

implementation ('org.web3j:core:4.10.0')

Android:

implementation ('org.web3j:core:4.8.7-android')

Web3j includes integration tests for running against a live Ethereum client. If you do not have a client running, you can exclude their execution as per the below instructions.

To run a full build (excluding integration tests):

$ ./gradlew check

To run the integration tests, you will need to set up these variables in order to pull the Docker images from the Docker Hub registry:

• registry.username
• registry.password

Then run the following command:

$ ./gradlew -Pintegration-tests=true :integration-tests:test

If you do not want the integration test to run:

$ ./gradlew -Pintegration-tests=false :test

Check the Docker client API for more information on configuration options.

Commercial support and training is available from web3labs.com.

Apache 2.0