Quick Overview
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. It enables you to work with Ethereum, without the additional overhead of having to write your own integration code for the platform.
Pros
- Easy integration with Java and Android projects
- Type-safe wrapper for working with smart contracts
- Supports both synchronous and asynchronous interactions
- Comprehensive documentation and active community support
Cons
- Learning curve for developers new to blockchain technology
- Performance may be slower compared to native implementations
- Limited support for other blockchain platforms beyond Ethereum
- Dependency on external Ethereum nodes for certain operations
Code Examples
- Connecting to an Ethereum client:
Web3j web3 = Web3j.build(new HttpService("https://mainnet.infura.io/v3/YOUR-PROJECT-ID"));
- Sending Ether:
TransactionReceipt transactionReceipt = Transfer.sendFunds(
web3, credentials, "0x<address>", BigDecimal.valueOf(1.0), Convert.Unit.ETHER
).send();
- Deploying a smart contract:
YourSmartContract contract = YourSmartContract.deploy(
web3, credentials, GAS_PRICE, GAS_LIMIT, <constructor parameters>
).send();
- Calling a smart contract function:
TransactionReceipt receipt = contract.someFunction(<parameters>).send();
Getting Started
To start using Web3j in your Java project:
- Add the Web3j dependency to your project's
build.gradlefile:
dependencies {
implementation 'org.web3j:core:4.9.4'
}
- Create a Web3j instance:
Web3j web3 = Web3j.build(new HttpService("https://mainnet.infura.io/v3/YOUR-PROJECT-ID"));
- Load credentials:
Credentials credentials = WalletUtils.loadCredentials("password", "/path/to/walletfile");
- Now you can interact with the Ethereum network using the
web3instance and yourcredentials.
Convert 
designs to code with AI
Introducing Visual Copilot: A new AI model to turn Figma designs to high quality code using your components.
Try Visual CopilotREADME
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!
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
- 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
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 for further instructions on using Web3j.
Maven
Java:
<dependency>
<groupId>org.web3j</groupId>
<artifactId>core</artifactId>
<version>4.14.0</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
Java:
implementation ('org.web3j:core:4.14.0')
Android:
implementation ('org.web3j:core:4.12.3-android')
Build instructions
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.usernameregistry.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
Commercial support and training
Commercial support and training is available from web3labs.com.
License
Apache 2.0
Convert designs to code with AI
Introducing Visual Copilot: A new AI model to turn Figma designs to high quality code using your components.
Try Visual Copilot