Exposing Apex functionality through Rest Service

Here is a quick demo on exposing Apex Class functionality to external Systems through REST service.

Step 1: Create a apex class with all the fields required in REST request.
global class LeadInfoParser {
    global String LastName{get;set;}
    global String FirstName{get;set;}
    global String Company{get;set;}
    global String email{get;set;}
    global String Phone{get;set;}
    global String LeadStatus{get;set;}    

}

Step 2:To declare a class as a custom endpoint, you only need to annotate a global class with “@RestResource” and define the name of the endpoint.
In the below example, REST Service endpoint will be 
https://salesforcehostname/services/apexrest/LeadService

@RestResource(urlMapping='/LeadService/*')
global without sharing class LeadService {
    @HttpPost
    global static String createLead(LeadInfoParser leadrec){
        Lead leadObj = new Lead();
        leadObj.FirstName =leadrec.FirstName;
        leadObj.LastName=leadrec.LastName; 
        leadObj.Phone=leadrec.Phone;
        leadObj.email=leadrec.email; 
        leadObj.Company = leadrec.Company;
        leadObj.Status = leadrec.LeadStatus;             
      
        Database.saveResult saveResult = database.insert(leadObj,false);
        if(saveResult.isSuccess()){
            System.debug('Record Id:'+saveResult.getId());
        }
        else{
            System.debug('saveResult:'+saveResult.getErrors());
        }
        //Response
        JSONGenerator gen=JSON.createGenerator(true);     
        gen.writeStartObject();
        gen.writeStringField('message','Lead record is created Successfully');
        gen.writeEndObject();     
        String responseString= gen.getAsString();
        return responseString;
    }

}

REST Service is now ready with these two simple steps. We can quickly test this REST service using workbench.developerforce.com.

Request Body:
{"leadrec":{
   "FirstName":"Laxman",
   "LastName":"Vattam",
   "Company":"Google",
   "LeadStatus":"Open",
   "email":"laxmanVattam@gmail.com",
   "Phone":"+1123456"

 }

A lead should have been created successfully in Salesforce. REST service is now ready for external systems to call.
We can use @HttpGet similar to @HttpPost example above.

Developers can tailor the REST API to suit the business needs of their application. An endpoint can be defined with an Apex Class using the @RestResource annotation, and the method annotations allow the endpoint to behave specifically for creating, updating, deleting and querying data within the instance.