Change Data Capture (also known as change events) in Salesforce refers to a special type of platform event in which messaging events are created based on changes to records of specified Salesforce entities like Account or Contact. Events are marked by a specific change type--CREATE, UPDATE, DELETE, UNDELETE (with additional "Gap" events when the creation of events are not possible)--allowing the subscriber to react appropriately. In Salesforce Trailhead, they are covered in the latter half of the Design Event-Driven Apps for Real-Time Integration trail. Note to some degree you can also "enrich" the messages with always-to-be-provided fields helpful for processing, see the Trailhead tutorial for more information. Enrichment does carry a risk however of having multiple messages with the same ReplayID.
I added a Spring Boot Salesforce Event Listener sample to Github that shows how change events to the Account entity can be captured and logged. To use, first create a Salesforce connected app and from the Change Data Capture screen in Salesforce Setup enable messages from the Account entity. Then rename and configure the CDC Listener application.properties~template file as explained in that file. The application can then be run as any other Spring Boot app, e.g., from IntelliJ IDEA or via command-line using
gradle bootRun. Any changes you make to Accounts will result in logged output from the CDC Listener. For the purposes of this sample the CDC Listener presently reports on changes to just three Account fields--name (a String), rating (an enum), and number of employees (an int). However, it is easy to modify the AccountCDCEvent.Payload class to include whatever Account fields desired.
Sample output while editing accounts:
n.g.c.processor.AccountCDCProcessor : Account added: 0015e000002pK7EAAU, name Glen's First Account, employee count 12, rating Hot n.g.c.processor.AccountCDCProcessor : Account updated: 0015e000002pK7EAAU: Rating to Warm n.g.c.processor.AccountCDCProcessor : Account updated: 0015e000002pK7EAAU: Num employees to 15 Rating to null n.g.c.processor.AccountCDCProcessor : Account added: 0015e000002pNwUAAU, name Glen's Second Account, employee count 50, rating Hot n.g.c.processor.AccountCDCProcessor : Account deleted: 0015e000002pNwUAAU n.g.c.processor.AccountCDCProcessor : Account undeleted: 0015e000002pNwUAAU, name Glen's Second Account, employee count 50, rating Hot
For production, the potential for Gap events will need to be handled, see the Salesforce documentation for suggested strategies.