Rest Web Service Apex Code Sample.

Generally there are 6 annotation used to expose an Apex class as a RESTful Web service.

1. @RestResource(urlMapping='/yourUrl') ==> This should be used above class declaration. Where value of urlMapping denotes your endpoint.
2. @HttpDelete ==>  This should be used above web method declaration.
3. @HttpGet ==>  This should be used above web method declaration.
4. @HttpPatch ==>  This should be used above web method declaration.
5. @HttpPost ==>  This should be used above web method declaration.
6. @HttpPut ==>  This should be used above web method declaration.

Scenario : Create a simple rest web service, which has a simple web method which will return a string as a response.

Solution: Below code base is a simple rest web service example in Apex.
Now for simplicity, we are simply used @HttpGet annotation for the below web method.

/**
 * Rest Web Service Example.
 **/
@RestResource(urlMapping='/RestWSSampleExmpl/*')
global with sharing class RestWSSample
{
 @HttpGet
 global static String getRestSampleResponse()
 {
  return 'Success Response.';
 }
}

Note: Apex REST supports two formats for representations of resources: JSON and XML.