Web3j listen event from a contract

Question

I want to listen to event Sync from a contract.

In javascript, I managed like this (this is to understand better what I want):

const contract = new web3.eth.Contract(abi, contractAddress);

const syncEvent = contract.events["Sync"];

syncEvent().on('data', function(event){
    console.log(event);
}).on('error', function(error){
    console.log(error)
}).on("changed", function(isSyncing){
    console.log(isSyncing);
});

In java I managed only this:

Web3j web3jWS = Web3j.build(new WebSocketService("wss://...", false));

EthFilter filter = new EthFilter(
    DefaultBlockParameterName.LATEST,
    DefaultBlockParameterName.LATEST,
    contractAddress
);

But I have no idea how to continue this, even if it's right my code.

How I can listen to the event Sync with Web3j?

Answer 1

    try {
        WebSocketService ws = new WebSocketService("ws://node-01:8545", true);
        ws.connect();
        Web3j web3 = Web3j.build(ws);
        EthFilter filter = new EthFilter(
            DefaultBlockParameter.valueOf(BigInteger.ZERO),
            DefaultBlockParameter.valueOf("latest"),
            contractAddress     
        );          
        web3.ethLogFlowable(filter)
            .onExceptionResumeNext( Flowable.empty() )
            .subscribe( log -> {
                
                System.out.println("EVENT !!!");
                System.out.println( log.getData() );
                
            }, error -> {
                System.out.println( error.getMessage() );
            }
        );          
        
    } catch (Exception e) {
        e.printStackTrace();
    }