Web3j: Web3 Java Ethereum Dapp API

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.

NEW! Get involved! Copy Chapter

Since Web3J moved under Hyperledger we started to do Web3J Contributors calls every 2 weeks!
Subscribe to our community page and to see check our call schedule.
Your contribution matters!

• Community Link - Check our last updates!
• Calendar Invite - Add the contributor call to your calendar!

Features Copy Chapter

• 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.

QuickStart Copy Chapter

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/hyperledger/web3j-installer/main/installer.ps1'))

Create a new project by running:

$ web3j new

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

Please head to the [Web3j Documentation](https://docs.web3j.io) for further instructions on using Web3j.

Maven Copy Chapter

Java:

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>5.0.3</version>
</dependency>

Note: The Web3j Java binaries are compiled using Java 21. Java 21 or a more recent version is required to use Web3j
as a dependency.

Android:

<dependency>
  <groupId>org.web3j</groupId>
  <artifactId>core</artifactId>
  <version>4.12.3-android</version>
</dependency>

Gradle Copy Chapter

Java:

implementation ('org.web3j:core:5.0.3')

Android:

implementation ('org.web3j:core:4.12.3-android')

Build instructions Copy Chapter

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.

Projects using Web3j Copy Chapter

Commercial support and training Copy Chapter

Commercial support and training is available from
web3labs.com.

License Copy Chapter

Apache 2.0