Custom transform example

Custom parser converts an internal Joule StreamEvent into a domain object

Objective

The objective of this example is to demonstrate how to implement a custom CustomTransformer to convert an internal Joule StreamEvent object to a domain-specific Quote object.

On how to implement a custom transformation, reference the CustomTransform API documentation.

Example

public class QuoteTransformer implements CustomTransformer<Quote> {

    public QuoteTransformer() {
        // Required
    }

    @Override
    public Collection<Quote> transform(Collection<StreamEvent> payload) throws TranslationException {
        Collection<Quote> quotes = new ArrayList<>();
        if( payload!= null) {
            for(StreamEvent e : payload){
                quotes.add(transform(e));
            }
        }
        return quotes;
    }

    @Override
    public Quote transform(StreamEvent payload) throws TranslationException {
        return new Quote(
                (String)payload.getValue("symbol"),
                (double)payload.getValue("mid"),
                (double)payload.getValue("bid"),
                (double)payload.getValue("ask"),
                (long)payload.getValue("volume"),
                (double)payload.getValue("volatility"),
                (long)payload.getEventTime(),
                (Date)payload.getValue("date")
                );
    }
}

Explanation

The example demonstrates a custom implementation of the CustomTransformer interface, specifically designed to convert a StreamEvent objects to domain specific types.

Constructor

The constructor is required but does not contain any specific logic for this example.

Transform single event method

This core method that converts the StreamEvent object to a single domain specific object. This is performed by a simple attribute mapping from the StreamEvent to Quote constructor parameter requirements.

@Override
public Quote transform(StreamEvent payload) throws TranslationException {
return new Quote(
        // Mapping
        ... 
        );
}

Transform batch events method

This method is called when in micro-batching mode. It takes a collection of StreamEvents and converts to a collection of domain specific events using the defined single event transform method.

@Override
public Collection<Quote> transform(Collection<StreamEvent> payload) throws TranslationException {
    Collection<Quote> quotes = new ArrayList<>();
    if( payload!= null) {
        for(StreamEvent e : payload){
            quotes.add(transform(e));
        }
    }
    return quotes;
}

Quote attributes description

Attributes	Description	Type
eventTime	The time the quote was recorded	Date / time
symbol	The symbol of the asset being quoted	String
bid	The bid price of the asset	Double
ask	The ask price of the asset	Double
volatility	The volatility of the asset	Double
volume	The volume of trades for the asset	Double
date	The date the quote was issued	Date