[Ethereum] how to get latest block number using web3j java APIs

web3j

I ask the network for current balance of the address i want to keep track. after that i want to detect/listen incoming deposits starting at the latest block number at the start of my program/server. now the problem is how to find the latest block number at that time? it looks like there is an API in web3js (java script) but not in web3j (java). I am connected to rinkeby testnet via infura node.

Best Answer

This is the easiest way

Web3j web3j = Web3j.build(new HttpService("https://rinkeby.infura.io/v3/......."));
Block block = web3j.ethGetBlockByNumber(DefaultBlockParameterName.LATEST, false).send().getBlock();
System.out.println(block.getNumber().toString());

Related Solutions

Web3j – How to Deploy Smart Contracts Using Web3j Java Library

you need to create a Function Object for your smart contract constructor then in data field were you put compiled solidity add the decode result of this function 'compiled smart contract'+'decoded function of the constructor'

[Ethereum] Problems calling Smart Contract function in Java using Web3j

modify your build.gradle to this and rebuild (i usually use maven), the problem was probably with okhttp used in web3j

dependencies {
    // https://mvnrepository.com/artifact/org.web3j/core
    implementation 'org.web3j:core:4.8.4'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

dependencies{
    implementation group: 'com.squareup.okhttp3', name: 'okhttp', version: '4.3.1'
    implementation("com.squareup.okhttp3:logging-interceptor:4.3.1")
}

test {
    useJUnitPlatform()
}

That will solve the problem, but another error could accrue.so :

Try to find which solidity version is supported by Web3j (cause 0.8 is very new) and then deploy the contract with the new version and generate the java code to that contract using Web3j

here are some docs about web3j contract interaction http://docs.web3j.io/latest/smart_contracts/interacting_with_smart_contract/

this method could be helpful to check if the contract is valid before calling your method: http://docs.web3j.io/latest/smart_contracts/contract_validity/ http://docs.web3j.io/latest/quickstart/#loading-a-smart-contract

Another thing in your contract you are using "public pure" method which does not need a tx, try better the storage contract, it has 2 methods the first one is a transaction and return a tx hash, the other method is a get method to get the value without a transaction https://docs.soliditylang.org/en/v0.4.24/introduction-to-smart-contracts.html

Try it and tell me if everything works

Best Answer

Related Solutions

Web3j – How to Deploy Smart Contracts Using Web3j Java Library

[Ethereum] Problems calling Smart Contract function in Java using Web3j

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