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

Last updated