How to get Salesforce Custom Field Ids in Apex

We can get the Ids of Salesforce Object’s custom fields in the Apex code using Tooling API. Following is the example code for the same:

String objectDevName = 'ObjectName';
ToolingAPI toolingAPI = new ToolingAPI();
List objectData = (List)toolingAPI.query('Select Id From CustomObject Where DeveloperName = \'' + objectDevName + '\'').records;
Map customFieldIds = new Map();
if (objectData!=null && !objectData.isEmpty()) {
ToolingAPIWSDL.sObject_x objectDetails = objectData[0];
Id objectId = objectDetails.Id;
List customFields = (List)toolingAPI.query('Select Id, DeveloperName From CustomField Where TableEnumOrId = \'' + objectId + '\'').records;
for(ToolingAPIWSDL.sObject_x fieldDetails: customFields){
customFieldIds.put(fieldDetails.DeveloperName, String.valueOf(fieldDetails.Id).substring(0, 15));
}
}