Summary

Pattern	Category	The 10-Second Summary	Real-World Backend Context
Abstract Factory	Creational	A factory of factories. Creates families of related objects.	Swapping entire cloud SDKs (e.g., an AWS Factory creating SQS/S3 vs. a Local Factory creating Kafka/MinIO).
Singleton	Creational	Ensures only one instance of a class exists.	The default behavior of a Spring Bean.
Prototype	Creational	Clones an existing object instead of building from scratch.	Using @Scope("prototype") in Spring for stateful, non-shared components.
Bridge	Structural	Separates an interface from its implementation so both can vary independently.	Your service layer interface (Abstraction) talking to different database drivers (Implementation).
Composite	Structural	Treats a group of objects the exact same way as a single object (Tree structure).	Parsing JSON/XML structures, or representing a hierarchical file system.
Flyweight	Structural	Shares massive amounts of fine-grained data to save RAM.	The Java String pool, or caching standard AWS Region configurations across millions of requests.
Chain of Responsibility	Behavioral	Passes a request along a chain of handlers until one handles it.	Spring Security Filter Chain (Checking CORS, then Auth, then Roles).
Command	Behavioral	Turns a request into a standalone object containing all info about it.	Sending tasks to an AWS SQS queue or a Kafka topic to be executed asynchronously.
Iterator	Behavioral	Lets you traverse a collection without exposing its underlying representation.	Using List.iterator() or Stream API to loop through database query results.
Memento	Behavioral	Captures and restores an object’s internal state (Undo mechanism).	Implementing rollback features in distributed transactions (Saga pattern).
Template Method	Behavioral	Defines the skeleton of an algorithm in a base class, letting subclasses override specific steps.	Spring’s JdbcTemplate or RestTemplate.
Visitor	Behavioral	Separates an algorithm from the object structure on which it operates.	Exporting a massive graph of distinct microservice logs into a single unified JSON report.