–> 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

–> Classes with REST annotation should be defined as global.

–> Methods with REST annotation should be defined as global static.

–> @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.

Let’s create an account by sending a parameter through API url.

Step 1: Create an apex class  say ‘restExample’.

@RestResource(urlMapping='/example')
global class restExample {
	/**
    * Webkul Software.
    *
    * @category  Webkul
    * @author    Webkul
    * @copyright Copyright (c) 2010-2016 Webkul Software Private Limited (https://webkul.com)
    * @license   https://store.webkul.com/license.html
    */
    
    // Method to get the Account name from parameter
    
    @HttpGet
    global static void getAccountName() {
        RestRequest req = RestContext.request;
        RestResponse res = RestContext.response;
        res.addHeader('Content-Type', 'application/json');
        String accountName = req.params.get('account_name');
      	
        // Call the method to create Account
        if(accountName != null){
        	restExample.createAcc(accountName);
        } else {
            restExample.createAcc();
        }
        
    }
    
	// Create Account when param is set 
    public static void createAcc(String accName) {
        try{
            
            Account acc = new Account(Name = accName, Description = 'Account is created by REST API');
            insert acc;
            
        } catch (Exception ex) {
           system.debug(ex.getMessage());
        }
    }
    
    // Create Account when param is not set 
    public static void createAcc() {
        try{
            
            Account acc = new Account(Name = 'Name is not set', Description = 'Account is created by REST API');
            insert acc;
            
        } catch (Exception ex) {
            system.debug(ex.getMessage());
        }
    }
}

Step:2: Now, to expose above rest class create a site as shown below. Goto>> SetUp>> Develop>> Sites

# Register your domain:

# Create New Site 

# Copy the Default Web Address

# Now goto Public Access Setting :

# Provide Access to object which you want to expose in class.

# Expose Apex class :

That’s all for setting up of site.

Step 3:  Now paste  Default Web Address(which you have copied from site setting) by appending:

1). Without sending any parameter : ‘/services/apexrest/example’ . 

2).  With parameter : ‘/services/apexrest/example?account_name=Webkul’

Now, goto account page and verify your results.