#platform event

Extracting data from the source systems. This typically involves data from several source systems, and both relational and non-relational structures.

Transforming the data to fit operational needs, which can also include data quality levels. The transform stage usually applies a series of rules or functions to the extracted data from the source to derive the data for loading into the end target(s).

Loading the data into the target system. The target system can vary widely from database, operational data store, data mart, data warehouse, or other operational systems.

Most mature ETL tools provide a change data capture capability. This capability is where the tool identifies records in the source system that have changed since the last extract, which reduces the amount of record processing.

The "Platform Event" can be     publish or subscribe either programmatic(Trigger) or declarative(Process Builder). 

External integration can publish the Platform Event just by creating a record in Salesforce Platform Event object using either SOAP/REST API.

For external application like Java need to have a streaming API Bayeux - CometD protocol setup. 

Trigger

trigger ApprovalRequestEventSubscriber on Approval_Request_Event__e (after insert) {    Set<Id> supplierSpendInsertSet = new Set<Id>();    for(Approval_Request_Event__e evt : Trigger.new){        if(evt.Event_Type__c == 'Supplier Spend Insert'){// Condition 1            //Only one set for each condition         supplierSpendInsertSet.add(evt.Approval_Request_Id__c);        }/*else if(condition){ //Condition 2 //Any other condition }*/    }    if(! supplierSpendInsertSet.isEmpty()){ //only one handler for each set        ApprovalRequestEventSubscribeHandler.handleSupplierSpendInsertSet(supplierSpendInsertSet);    } }

Handler

Automatic Event Generator Batch Class

public with sharing class BatchLeadConvert implements Database.Batchable<SObject>,Database.RaisesPlatformEvents{

   private final String CONVERTED_STATUS = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true LIMIT 1].MasterLabel;

   public Database.QueryLocator start(Database.BatchableContext ctx){        return Database.getQueryLocator([SELECT Id FROM Lead WHERE ConvertedContactId = null]);    }

   public void execute(Database.BatchableContext ctx, List<Lead> records){        List<Database.LeadConvert> leadConverts = new List<Database.LeadConvert>();        for(Lead record:records){            Database.LeadConvert lc = new Database.LeadConvert();            lc.setConvertedStatus(CONVERTED_STATUS);            lc.setLeadId(record.Id);

           leadConverts.add(lc);        }        Database.convertLead(leadConverts, true);    }

   public void finish(Database.BatchableContext ctx){

   } }

Event Subscriber Trigger

trigger BatchApexErrorTrigger on BatchApexErrorEvent (after insert) { List<BatchLeadConvertErrors__c> errorLogList = new List<BatchLeadConvertErrors__c>();    for(BatchApexErrorEvent evt : Trigger.new){     BatchLeadConvertErrors__c errorLog = new BatchLeadConvertErrors__c();        errorLog.AsyncApexJobId__c = evt.AsyncApexJobId;        errorLog.Records__c = evt.JobScope;        errorLog.StackTrace__c = evt.StackTrace;        errorLogList.add(errorLog);    }    insert errorLogList; }

When you enable  Change Data Capture for a specific Standard Object or a Custom Object Salesforce Automatically create a corresponding Change Event Object for Example :

1. Account -> AccountChangeEvent

2. Employee__c -> Employee__ChangeEvent

If Change Data Capture enabled for for either a Standard or a Custom Object then in case of any DML operation for the same object records Salesforce creates corresponding Change Event record after the completion of the DML asynchronously.

After Insert trigger is also possible on Change Event Records for any asynchronous processing. Underneath Salesforce is implementing the Platform Event concept for even subscribing the event through streaming channel. Here is an example to subscribe to AccountChangeEvent from Workbench.

Channel Name : /data/AccountChangeEvent

Note : You can also test CDC at  https://salesforcelwc.herokuapp.com/

From Java : https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/code_sample_java_client_intro.htm

Note : You can also test platform event subscription at  https://salesforcelwc.herokuapp.com/

From Workbench :