How to check if geth node is running ,from web3j code

Question

I am connecting to Geth using Web3j plugin.

web3j = Web3j.build(new HttpService("http://<ip>:<port>")); // defaults to http://localhost:8545/

However, if the Geth node is not started, I need to throw an exception. How can I find if the Geth node is started or no using web3j java code ?

Answer 1

try {
    Web3j web3j = Web3j.build(new HttpService("LINK-TO-YOUR-NODE"));
    // this will cause the exception if web3j is not connected
    LOG.info("Connected to Ethereum client version: "
        + web3j.web3ClientVersion().send().getWeb3ClientVersion());
} catch (Exception e) {
    LOG.error("WEB3-Connection Error", e);
    // DO SOMETHING
}

The answer of TLHBM is also correct

Answer 2

web3j.netVersion().send().getNetVersion();

this code is getting blockchain chain ID(version)

we can use this kind of code for checking a connection

from this

Answer 3

RPC net_listening is available to check if provider is available (specifically over IPC where connection does not mean that RPC is available).

https://github.com/ethereum/wiki/wiki/JSON-RPC#net_listening

Web3j exposes this as netListening method.

web3j = Web3j.build(new HttpService("http://<ip>:<port>"));
if(web3j.netListening() ){
//Do rest of operations 
}