I use web3j in my Java application. In the smart contract, an event is defined.

 event sendEvent(string name);

I subscribed to that event in my app.

        .subscribe(doc -> {           
        }, throwable -> {
        }, () -> {
            System.out.println("End of research");

It works, But I noticed that Web3j listens to the Blockchain every 15 seconds.

That is not suitable for my application and I need to listen to what is happening inside the blockchain all the time.

How can I change the default value (15 sec)?

This is my code

WebSocketService ws = new WebSocketService("ws://localhost:8545", true);
        web3 = Web3j.build(ws);
  • in the ethereum mainnet a block is generated each ~15 seconds .. between those blocks nothing happens
    – Majd TL
    Jun 26, 2022 at 11:23
  • I'm using ganache, but it works when I use the same code using web3js in JavaScript, in my opinion, is related to the web3j library. Jun 26, 2022 at 11:38
  • Webj does not know that you are using ganache. I think it is configurable but anyway that was my answer to why it is set to 15 seconds
    – Majd TL
    Jun 26, 2022 at 11:45
  • I agree with you, it is configurable, but how? Jun 26, 2022 at 11:50

1 Answer 1


On ethereum mainnet a block is generated each 15 seconds. that is why 15 is the default value for events. however you can change this by using this build method:

     * Construct a new Web3j instance.
     * @param web3jService web3j service instance - i.e. HTTP or IPC
     * @param pollingInterval polling interval for responses from network nodes
     * @param scheduledExecutorService executor service to use for scheduled tasks. <strong>You are
     *     responsible for terminating this thread pool</strong>
     * @return new Web3j instance
    static Web3j build(
            Web3jService web3jService,
            long pollingInterval,
            ScheduledExecutorService scheduledExecutorService) {
        return new JsonRpc2_0Web3j(web3jService, pollingInterval, scheduledExecutorService);

I found this in this issue about slow events https://github.com/web3j/web3j/issues/233 and the answer referenced to this method and link https://github.com/web3j/web3j/blob/master/core/src/main/java/org/web3j/protocol/Web3j.java#L17

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