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Web3j: Web3 Java Ethereum Ðapp API

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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:

image

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.

Features

It has five runtime dependencies:

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/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.

Please head to the Web3j Documentation for further instructions on using Web3j.

Maven

Java:

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

Android:

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

Gradle

Java:

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

Android:

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

Commercial support and training is available from web3labs.com.

License

Apache 2.0

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