Interacting with the smart contract from Java application (We3j)

Question

I have many questions about the workflow ( sequence ) of interacting with the smart contract from Java application, so I will first explain what I have done and then put my questions, and if something wrong in my understanding please let me know.

1- I have written smart contract 2- Use truffle to get the smart contract java wrapper.(contract.java) 3- Use testrpc to test the contract

I have 2 class uses testrpc accounts (credentials) to interact with the smart contract and call its functions

Each class (node1.java, node2.java) call a function in the smart contract called (send) to send their data to the chain.

I have added an event which trigger if the 2 nodes have sent there data

What I don't understand is, how I can let the java code ( Let say MainProgram.class) always check for that event. Because I need to check if both nodes send their data, then I will call another function to analyse this data.

How I can manage, control and check what transactions have been done or not, I mean how I can use the events in java code and let the code run forever and check if the this event happen, do action.

Hope I can explain what I need clearly

Thank you in advance.

Answer 1

In your java wrapper for each type of event in your SmartContract, there will be a function that looks like this:

public Observable<ApprovalEventResponse> approvalEventObservable(DefaultBlockParameter startBlock, DefaultBlockParameter endBlock) {

            ...                

            return typedResponse;
        }
    });
}

You can subscribe to this observable from your java code as follows:

contract.approvalEventObservable(DefaultBlockParameter.valueOf("Earliest"),DefaultBlockParameter.valueOf("Latest")).asObservable().subscribe( event ->{
    System.out.prtinln(event._approver);
});

This will replay all events that have occurred and print the attribute of previous events and will also print new events when they occur.