What is RestResource Annotation in Salesforce?

•  REST annotation enables you to expose an Apex class or an Apex method as a REST resource. In salesforce, there are six REST annotations, that is :

1). @RestResource(urlMapping=’/your url’)

2). @HttpGet

3). @HttpPost

4). @HttpPut

5). @HttpPatch

6). @HttpDelete

7). @HttpHead

• Classes with REST annotation should be defined as global.
• Methods with REST annotation should be defined as global static.

I am giving you 1 example of HttpGet...

@HttpGet is used at method level. This method is called when a HTTP GET  request is sent. To expose your apex class as REST resource you should use @RestResource(urlMapping=’/your url’) annotation at class level as shown below.

@RestResource(urlMapping='/your_url')
global class restExample {

@HttpGet
global static void exampleMethod() {

// Write your code here
}
}

Here url mapping is relative to https://instance.salesforce.com/services/apexrest/.

• If your class is in namespace say ‘abc’, then API  url must be as follows:
•  https://instance.salesforce.com/services/apexrest/abc/you_url
  URL are case-sensitive.

Hi

The @RestResource annotation is used at the class level and enables you to expose an Apex class as a REST resource.

These are some considerations when using this annotation:The URL mapping is relative to https://instance.salesforce.com/services/apexrest/.
A wildcard character (*) may be used.
The URL mapping is case-sensitive. A URL mapping for my_url will only match a REST resource containing my_url and not My_Url.
To use this annotation, your Apex class must be defined as global.

Thanks