Custom parsing example

Custom parser converts a domain Quote object into an internal Joule StreamEvent

Objective

The objective of this example is to demonstrate how to implement a custom StreamEventParser to convert domain-specific objects, such as a Quote, into the required Joule StreamEvent object ready for processing.

Example

@JsonRootName(value = "quote parser")
public class QuoteToStreamEventParser implements StreamEventParser {

    public QuoteToStreamEventParser() {
        // Required
    }

    @Override
    public Collection<StreamEvent> translate(Object o) throws TranslationException {
        Collection<StreamEvent> events = null;
        if(o instanceof Quote){
            Quote quote = (Quote) o;
            StreamEvent event = new StreamEvent("quote");
            event.setEventTime(quote.time());
            event.addValue("symbol", quote.symbol());
            event.addValue("bid", quote.bid());
            event.addValue("ask", quote.ask());
            event.addValue("volatility", quote.volatility());
            event.addValue("volume", quote.volume());
            event.addValue("date", quote.date());

            events = Collections.singletonList( event);
        }
        return events;
    }
}

Explanation

The example demonstrates a custom implementation of the StreamEventParser interface, specifically designed to convert a Quote object into a StreamEvent.

Parser Annotation

The class annotation defines the parser DSL element, indicating the parser's role in converting Quote objects. It aids in custom serialisation settings. This is required.

Constructor

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

Translate method

The core method that converts the input object into a collection of StreamEvent objects.

This example the method checks if the input object is an instance of Quote. If not, it returns null, indicating non-valid conversion.

Otherwise, the quote attributes are mapped in to a single StreamEvent which is then placed in to a Collections.singletonList() and returned as a collection, as required by the method's signature.

@Override
public Collection<StreamEvent> translate(Object o) throws TranslationException {
    Collection<StreamEvent> events = null;
    if(o instanceof Quote){
        ...
    }
}

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