Salesforce: Consuming REST Web Service

Overview

Salesforce can act as a client calling an external REST API by utilizing Apex callouts. This article provides a step-by-step guide on how to consume a REST service in Salesforce.

Step 1: Enable Callouts

To enable callouts in Salesforce, follow these steps:

• Add the external endpoint to Remote Site Settings by navigating to Setup → Security → Remote Site Settings. This step is crucial as Salesforce blocks callouts by default.

Step 2: Apex Code to Consume REST Service

Below is a simple example of Salesforce consuming a REST API through Apex:

public class RestConsumerExample {
    public static void getWeatherData(String city) {
        // Prepare the HTTP request
        Http http = new Http();
        HttpRequest req = new HttpRequest();

        // Example external REST API endpoint
        String endpoint = 'https://api.example.com/weather/' + city;
        req.setEndpoint(endpoint);
        req.setMethod('GET');

        // Add headers if needed (e.g., authentication)
        req.setHeader('Authorization', 'Bearer YOUR_ACCESS_TOKEN');
        req.setHeader('Content-Type', 'application/json');

        // Send the request
        HttpResponse res = http.send(req);

        // Handle the response
        if (res.getStatusCode() == 200) {
            System.debug('Response Body: ' + res.getBody());
        } else {
            System.debug('Error: ' + res.getStatusCode() + ' ' + res.getStatus());
        }
    }
}

Step 3: Parsing JSON Response

To parse JSON responses in Salesforce, you can use JSON.deserialize to convert JSON into Apex objects. Here’s an example:

public class WeatherResponse {
    public String city;
    public String temperature;
    public String condition;
}

public class RestConsumerExample {
    public static WeatherResponse getWeatherData(String city) {
        Http http = new Http();
        HttpRequest req = new HttpRequest();
        req.setEndpoint('https://api.example.com/weather/' + city);
        req.setMethod('GET');
        req.setHeader('Authorization', 'Bearer YOUR_ACCESS_TOKEN');

        HttpResponse res = http.send(req);

        if (res.getStatusCode() == 200) {
            WeatherResponse wr = (WeatherResponse) JSON.deserialize(res.getBody(), WeatherResponse.class);
            return wr;
        } else {
            throw new CalloutException('Failed with status: ' + res.getStatusCode());
        }
    }
}

Step 4: Test Class Example

It is essential to write test classes to validate the callout logic. Here’s a test class example:

@isTest
private class RestConsumerExampleTest {
    @isTest static void testGetWeatherData() {
        // Mock the HTTP response
        Test.startTest();
        HttpResponse res = new HttpResponse();
        res.setStatusCode(200);
        res.setBody('{"city":"Cochin","temperature":"30C","condition":"Sunny"}');

        // Use HttpCalloutMock to simulate the external service
        Test.setMock(HttpCalloutMock.class, new WeatherMock());

        WeatherResponse wr = RestConsumerExample.getWeatherData('Cochin');
        Test.stopTest();

        System.assertEquals('Cochin', wr.city);
        System.assertEquals('30C', wr.temperature);
        System.assertEquals('Sunny', wr.condition);
    }
}

// Mock class
global class WeatherMock implements HttpCalloutMock {
    global HTTPResponse respond(HTTPRequest req) {
        HttpResponse res = new HttpResponse();
        res.setStatusCode(200);
        res.setBody('{"city":"Cochin","temperature":"30C","condition":"Sunny"}');
        return res;
    }
}

Explanation

Here are some key points to remember while consuming REST services in Salesforce:

• Http & HttpRequest: Apex classes used for making REST callouts.
• Remote Site Settings: Required to whitelist external endpoints.
• Headers: Used for authentication such as Bearer tokens and API keys.
• JSON.deserialize: Converts JSON responses into Apex objects.
• Test.setMock: Necessary for unit testing callouts as Salesforce prohibits real HTTP calls in tests.

Key Takeaways

• Salesforce can function as a REST client using Apex callouts.
• Always configure Remote Site Settings for external endpoints to ensure smooth callouts.
• Utilize JSON.deserialize to effectively parse responses into Apex objects.
• Write mock-based test classes to validate the functionality of callouts.