https://github.com/julius278/eth-web3j-java
spring boot application, which uses the web3j library to communicate with the ethereum (testnet) blockchain. The README also includes some challenges, where you can play around with web3j. Feel free to fork or clone the code.
https://github.com/julius278/eth-web3j-java
ethereum java smartcontracts spring-boot web3j
Last synced: 29 days ago
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spring boot application, which uses the web3j library to communicate with the ethereum (testnet) blockchain. The README also includes some challenges, where you can play around with web3j. Feel free to fork or clone the code.
- Host: GitHub
- URL: https://github.com/julius278/eth-web3j-java
- Owner: Julius278
- Created: 2024-02-05T17:26:44.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2025-02-26T12:23:15.000Z (over 1 year ago)
- Last Synced: 2025-08-21T12:52:30.202Z (10 months ago)
- Topics: ethereum, java, smartcontracts, spring-boot, web3j
- Language: Java
- Homepage:
- Size: 203 KB
- Stars: 0
- Watchers: 2
- Forks: 1
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- Codeowners: .github/CODEOWNERS
Awesome Lists containing this project
README
On the [bottom of the README](#web3j-challenges) there are some challenges to get into the topic. Have fun!
# General Web3J information
The application takes advantage of the [Web3J library](https://github.com/web3j/web3j) to communicate with the ethereum blockchain.
To be correct, you connect to an ethereum (main or test net) node via [JSON-RPC](https://www.jsonrpc.org/) connection and retrieve the information this specific node/chain provides.
``` XML
org.web3j
core
4.10.3
```
To also work with Solidity SmartContracts and interact with them within your code, you will have to add two build plugins.
The `web3j-maven-plugin is needed` to generate the Java wrapper classes for your Solidity contracts.
The `build-helper-maven-plugin` is needed to include the generated classes into your /target/ folder.
More details in the pom.xml
``` XML
org.web3j
web3j-maven-plugin
${web3j-maven-plugin.version}
...
org.codehaus.mojo
build-helper-maven-plugin
...
```
# Usage
## keyfile
the given keyfile.json (/src/main/resources/) is a newly generated wallet with some SEPOLIA or Holesky testnet eth.
If you test with this application, you can test with this wallet or create / include your own.
## api development / testing software
tools like Postman or Insomnia are great for testing REST endpoints.
Pros use cURL ;)
### Postman
example for postman or other testing tools:
### cURL
example for the blockNumber endpoint:
``` bash
curl --location 'http://localhost:8080/api/eth/blockNumber'
```
## different ETH node
It is also possible to use every other node by simply replace the _eth.node.address_ variable in application.properties.
You can also override the node by defining it via environment variables (`ETH_NODE_ADDRESS=http....`)
As this is just a showcase / fun project / poc / whatever, there are no special profiles for main or test net.
# Web3j challenges
Hey, glad you're ready to learn about Web3j.
Feel free to fork (or just clone) and play around.
If you want to track your transactions, you can observe them on the testnet block explorer:
https://holesky.etherscan.io/address/0x9f162b41fa8e44f885bedae410418145a4e8ed06
## Challenge 1
* Git clone project (https://github.com/Julius278/eth-web3j-java)
``` bash
git clone https://github.com/Julius278/eth-web3j-java.git
```
* (if you have a GitHub account and are familiar with the platform, you can also fork and clone your own repository)
* you're on the "main" branch now
* Build the Java project on the project root directory
``` bash
mvn clean install
```
* alternatively you can use the maven plugin of your IDE, here is an example for Intellij
* it should show a BUILD SUCCESS message
* To play around with the existing functionality you can start the spring boot service
``` bash
mvn spring-boot:run
```
or use the [PlayAroundDemo](https://github.com/Julius278/eth-web3j-java/blob/main/src/main/java/com/julius/spring/boot/ethweb3/demo/PlayAroundDemo.java)
* Everything is prepared
* you can just start by choosing your PropertyName and ID (uniqueness is checked on the PropertySafe)
* you don't have to worry about setting up a node, wallet, funding of your account, transaction fees or the connection
## Challenge 2
* Adjust a given solidity contract (Property.sol, e.g. a new getter function)
``` Solidity
function getTest() external view returns (string memory){....}
```
* Build the Java maven project again
``` bash
mvn clean install
```
* Use the new getter function in your Java code
* A possible solution is shown in branch: challenge-3-solution, in short you can see it [here](https://github.com/Julius278/eth-web3j-java/pull/1)
## Challenge 3
Let's do a calculation on-chain
* Add a new solidity function which takes two numbers (int) and returns an int (like sum or multiply it)
* one hint to Integers
* Solidity supports 64 different integer types
* int results in Solidity to int256
* int in Solidity is way bigger than the normal int in Java, so in Java you will have to use BigInteger
* Build the Java maven project again
* Use the new function in your Java code
* A possible solution is shown in branch: challenge-3-solution, in short you can see it [here](https://github.com/Julius278/eth-web3j-java/pull/2)
## Challenge 99
Write some units tests for your new code ;)