HTTP Callouts: Http, HttpRequest, HttpResponse

HttpRequest request = new HttpRequest();
request.setEndpoint('https://api.example.com/shipping-rates');
request.setMethod('GET');
request.setHeader('Content-Type', 'application/json');

1. HttpRequest request = new HttpRequest(); — an empty request object.
2. request.setEndpoint('https://api.example.com/shipping-rates'); — the URL to call.
3. request.setMethod('GET'); — the HTTP verb.
4. request.setHeader('Content-Type', 'application/json'); — metadata the external API expects.

HttpRequest is built up piece by piece: setEndpoint (the URL), setMethod (GET, POST, PUT, DELETE), and setHeader for any metadata the external API requires — this is the object Module 31's mock classes ultimately received as their respond(request) parameter.

Http http = new Http();
HttpResponse response = http.send(request);

if (response.getStatusCode() == 200) {
    Map<String, Object> parsed = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
    Decimal rate = (Decimal) parsed.get('rate');
} else {
    System.debug('Callout failed with status: ' + response.getStatusCode());
}

1. Http http = new Http(); — the class that actually performs the call.
2. HttpResponse response = http.send(request); — sends the request built earlier, blocking until a response arrives.
3. (blank line)
4. if (response.getStatusCode() == 200) { — checks the response's status code before trusting its body.
5. Map<String, Object> parsed = (Map<String, Object>) JSON.deserializeUntyped(response.getBody()); — Lesson 2's parsing, applied to a real response body.
6. Decimal rate = (Decimal) parsed.get('rate'); — extracts the needed value.
7. } else { — the failure branch.
8. System.debug('Callout failed with status: ' + response.getStatusCode()); — logs the failure rather than assuming success.
9. } — closes the if/else.

http.send(request) actually makes the call, returning an HttpResponse — getStatusCode() (Lesson 6's 200/500 pattern from Module 31) and getBody() (Lesson 2's JSON.deserializeUntyped) are exactly the methods every mock's fabricated response provided during testing.

HttpRequest request = new HttpRequest();
request.setEndpoint('https://api.example.com/orders');
request.setMethod('POST');
request.setHeader('Content-Type', 'application/json');

Map<String, Object> orderData = new Map<String, Object>{'productId' => 'W123', 'quantity' => 2};
request.setBody(JSON.serialize(orderData));

HttpResponse response = new Http().send(request);

1. HttpRequest request = new HttpRequest(); — a new request.
2. request.setEndpoint('https://api.example.com/orders'); — the target URL.
3. request.setMethod('POST'); — this time, POST, since data is being sent.
4. request.setHeader('Content-Type', 'application/json'); — tells the API the body is JSON.
5. (blank line)
6. Map<String, Object> orderData = new Map<String, Object>{'productId' => 'W123', 'quantity' => 2}; — the data to send, as a map.
7. request.setBody(JSON.serialize(orderData)); — Lesson 2's JSON.serialize, turning the map into the request's actual body text.
8. (blank line)
9. HttpResponse response = new Http().send(request); — sends it.

setBody combined with Lesson 2's JSON.serialize is the complete pattern for sending data to an external API, not just reading from one — this is genuinely everything a real callout needs.