How to properly close web3 after execution? - Java

Question

Here is what I am trying to do:

String amt = Web3j.build(new HttpService("https://ropsten.infura.io/v3/123blahblah"))
.ethGetBalance("0xblahblah", DefaultBlockParameterName.LATEST)
.send().getBalance().toString();

System.out.println(amt);

It prints the balance in wei nicely. However, the Web3 does not close and the application simply hangs. I am afraid that this would be a memory overflow if not managed properly and if too many calls are made. Also, this could lead to a potential security issue on the backend. So, the question is, how do I close the web3 as soon as I get the balance data I need ?

I've tried web3.shutdown() but it doesn't do anything.

Edit: I've noticed that there is a timeout and that it closes after several minutes. Still, I need to close it immediately after getting the data.

Edit2: This is obviously due to OkHttpClient. Related question/answer https://stackoverflow.com/questions/29055724/okhttpclient-close-connection

Answer 1

Yeah, alright, I got it. Here is the code if anyone else needs it:

import okhttp3.OkHttpClient;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.DefaultBlockParameterName;
import org.web3j.protocol.http.HttpService;

import java.io.IOException;

public class testBalance3 {

    public static void main(String[] args) throws IOException {

        okhttp3.OkHttpClient httpClient = new OkHttpClient();
        Web3j web3 = Web3j.build(new HttpService("https://ropsten.infura.io/v3/123blahkeyblahblah", httpClient));
        String amt = web3.ethGetBalance("0xblablahbla", DefaultBlockParameterName.LATEST).send().getBalance().toString();
        System.out.println(amt);
        httpClient.connectionPool().evictAll();

    }

}