Blockchain as a Service:Event Interface

How it works

Each subscription method registers a listener on the BaaS node. When a matching event occurs, the node calls your EventHandler.handle(Message message) implementation with an event-specific message object.

The EventModelType parameter controls the delivery mode:

Use PUSH for real-time event processing. Use PULL when your application polls on its own schedule.

All subscribe methods return a boolean: true if the subscription was registered successfully, false if an error occurred.

listenAccount

Subscribes to events for a specific account.

Signature

public boolean listenAccount(Identity identity, EventHandler handler, EventModelType type)

Parameters

Response

Example

// Define the event handler
EventHandler handler = new EventHandler() {
    @Override
    public void handle(Message message) {
        EventAccountMessage eventAccountMessage = (EventAccountMessage) message;
        // Process the account event
    }
};

// Specify the account identity (account: Tester001)
Identity identity = new Identity("c60a9d48105950a0cca07a4c6320b98c303ad42d694a634529e8e1a0a16fcdb5");

// Subscribe using PUSH mode
boolean result = sdk.getEventService().listenAccount(identity, handler, EventModelType.PUSH);

listenContract

Subscribes to events for a specific smart contract.

Signature

public boolean listenContract(Identity identity, EventHandler handler, EventModelType type)

Parameters

Response

Example

// Define the event handler
EventHandler handler = new EventHandler() {
    @Override
    public void handle(Message message) {
        EventContractMessage eventContractMessage = (EventContractMessage) message;
        // Process the contract event
    }
};

// Specify the contract identity
Identity identity = new Identity("a7937b64b8caa58f03721bb6bacf5c78cb235febe0e70b1b84cd99541461a08e");

// Subscribe using PUSH mode
boolean result = sdk.getEventService().listenContract(identity, handler, EventModelType.PUSH);

listenTopics

Subscribes to events for one or more topics.

Signature

public boolean listenTopics(List<String> topics, EventHandler handler, EventModelType type)

Parameters

Response

Example

// Define the event handler
EventHandler handler = new EventHandler() {
    @Override
    public void handle(Message message) {
        EventTopicsMessage eventTopicsMessage = (EventTopicsMessage) message;
        // Process the topic event
    }
};

// Build the topic list
List<String> topics = new ArrayList<>();
topics.add("call_contract");

// Subscribe using PUSH mode
boolean result = sdk.getEventService().listenTopics(topics, handler, EventModelType.PUSH);

listenBlock

Subscribes to block events.

Signature

public boolean listenBlock(EventHandler handler, EventModelType type)

Parameters

Response

Example

// Define the event handler
EventHandler handler = new EventHandler() {
    @Override
    public void handle(Message message) {
        // Process the block event
    }
};

// Subscribe using PUSH mode
boolean result = sdk.getEventService().listenBlock(handler, EventModelType.PUSH);

unListenAccount

Unsubscribes from account events.

Signature

sdk.getEventService().unListenAccount(identity)

Parameters

unListenContract

Unsubscribes from contract events.

Signature

public boolean unListenContract(Identity identity)

Parameters

unListenTopics

Unsubscribes from topic events.

Signature

public boolean unListenTopics(List<String> topics)

Parameters

unListenBlock

Unsubscribes from block events.

Signature

public boolean unListenBlock()