Parse the Response (JSON)
By the end of this lesson, you'll be able to:
- Write a typed wrapper class matching the response contract
- Deserialize the response body using that class
- Return the converted amount from the service method
Prerequisites: "Handle Authentication"
A typed class matching the response contract
public class ConversionResponse {
public Decimal convertedAmount;
public Decimal rate;
public String timestamp;
}This class's fields map directly onto Lesson 1's response contract — {"convertedAmount": 123.45, "rate": 0.054, "timestamp": "..."}. Module 36's JSON.deserialize(json, MyClass.class) (the typed version, not deserializeUntyped) needs exactly this kind of matching class.
Parsing and returning the result
public Decimal convert(Decimal amountInZar, String targetCurrency) {
HttpRequest request = new HttpRequest();
request.setEndpoint('callout:Currency_API/convert?from=ZAR&to=' + targetCurrency + '&amount=' + amountInZar);
request.setMethod('GET');
HttpResponse response = new Http().send(request);
ConversionResponse parsed = (ConversionResponse) JSON.deserialize(response.getBody(), ConversionResponse.class);
return parsed.convertedAmount;
}The method now genuinely does what Lesson 1's contract promised: takes an amount and a currency, calls the external API, and returns the actual converted Decimal — every earlier lesson's piece (the request, the auth, now the parsing) finally comes together into a complete, working method.
Exercise
Add a getRate() method to CurrencyConversionService that returns just the rate field from a conversion, reusing the same request/parse logic.
Show hint
Follow the same shape as convert(), returning parsed.rate instead.
Parse the Response (JSON) Quiz
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Summary
This lesson finally completes the method's core purpose — parsing the JSON response into a typed Apex class and returning the actual converted amount.