Restful webservice call improper response

Question

I have written an Restful GET API call to get 10 records based on some condition. In that I am returning all records as a string, while executing that method from Workbench I am not getting proper format. But in debug logs I am getting proper JSON response. Did I missed something?

Method:

@RestResource(urlMapping='/meetings/*')
global with sharing class RestWebshowMappingscls {
 @HttpGet
    global static string getMeetInviteDetails(){
        List<Meeting__c> metLst=new List<Meeting__c>();
        List<Mainwrapper> mainWrapLst;
        string finalqryvalue;
        metLst=[select id,name,Event__r.name,Meeting_ID__c,Meeting_with__c,Meeting_UUID__c,(select Meeting__r.name,Attendee__r.name,Unique_ID__c,Attendee_Status__c,Attendee_Name__c from Invites__r) from Meeting__c where Meeting_ID__c!=null limit 10];
        system.debug('metLst value' +metLst.size());
        if(metLst.size()>0 && metLst!=null){
          try{
              for(Meeting__c met:metLst){ 
                mainWrapLst=new List<Mainwrapper>();
                Mainwrapper mainWrap=new Mainwrapper();

                List<meeting> meetingWrapLst=new List<meeting>();
                meeting meetingWrap=new Meeting();             
                meetingWrap.mid=met.Meeting_ID__c;
                meetingWrap.meetingwith=met.Meeting_with__c;
                meetingWrap.eventName=met.Event__c;
                meetingWrap.meetinguuid=met.Meeting_UUID__c;
                meetingWrapLst.add(meetingWrap);

                List<invite> inwrap;
                List<invites__c> invlst;
                for(Invites__c inv : met.invites__r){
                    inwrap=new List<invite>();  
                    invite invt=new invite();   
                    invt.invitestatus=inv.Attendee_Status__c;
                    invt.inviteUniqueid=inv.Unique_ID__c;               
                    inwrap.add(invt) ;                           
                }
                meetingWrap.invites=inwrap;             
                mainWrap.data=meetingWrapLst;
                mainWrap.statusCode=200;
                mainWrap.status='Success';
                mainWrap.message='Details of Meetings';
                mainWrapLst.add(mainwrap);

                RestContext.response.responseBody = Blob.valueOf(JSON.serialize(mainWrapLst));
                finalqryvalue = JSON.serialize(mainWrapLst); 
                system.debug('finalqryvalue @@' +finalqryvalue);

            }
           } catch(exception ex){
               System.debug('exception type' +ex.getTypeName());
             }        
        }
        return finalqryvalue;
    }

//Wrapper to diplay values///
    global class Mainwrapper{
        public List<meeting> data;
        public integer statusCode;
        public string status;
        public string message;                  
    }        
    global class meeting{
        public string meetingwith;
        public string eventName;
        public string mid;
        public string meetinguuid;
        public List<invite> invites;
    }
    global class invite{
        public string invitestatus;
        public string inviteUniqueid;
    }    

}

Workbench screenshot:

Answer 1

Here is the issue:

RestContext.response.responseBody = Blob.valueOf(JSON.serialize(mainWrapLst));
finalqryvalue = JSON.serialize(mainWrapLst); 
system.debug('finalqryvalue @@' +finalqryvalue);

What you're debugging is in fact JSON. But your service is returning (i.e., its actual return value) a string, which is escaped automatically by Salesforce to produce JSON. Your web service return value is converted to JSON by Salesforce automatically; when this happens, your string - which is already JSON - gets escaped, and Workbench shows you that escaped string.

You don't need to set the response body and also return a value, and you actually don't need to do any explicit serialization at all. Just return your serializable structure:

global static List<Mainwrapper> getMeetInviteDetails() {
    // ...
    return mainWrapLst;
}

Salesforce will take care of marshalling it into JSON for you.