Stream Processing with SQL

This page shows how to processing stream data in HStreamDB with SQL using Java SDK.

Prerequisites

Make sure you have HStreamDB running and accessible.

Execute Real-time Query on Stream

You can execute a real-time query on stream using the HStreamClient.streamQuery() method:

final String TEST_STREAM = "test_stream";
Publisher<HRecord> publisher = client.streamQuery(
        "select * from " + TEST_STREAM +
        " where temperature > 30 emit changes;"
);
Observer<HRecord> observer = new Observer<HRecord>() {
    @Override
    public void onNext(HRecord hrecord) {
        System.out.println(hrecord);
    }
    @Override
    public void onError(Throwable t) {
        throw new RuntimeException(t);
    }
    @Override
    public void onCompleted() {
    }
};
publisher.subscribe(observer);

The HStreamClient.streamQuery() method return a Publisher object, and you need to provide an Observer object that contains your logic for processing the results returned by the query.